Soil Organic Matter And Biological Soil Quality Biology Essay

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Ghent University

Free University of Brussels

Belgium

BLACK OAT AS A NOVEL CATCH CROP:

EFFECTS ON SOIL ORGANIC MATTER AND BIOLOGICAL SOIL QUALITY

SHIHAB UDDIN

Promoter(s): Prof. Dr. Ir. Stefaan De Neve

Tutor: Jeroen De Waele

Academic Year 2012 - 2013

CONTENTS

ITEMS

PAGE

Table of contents…………………………………………………………………………………………………………………………….i

Lists of tables………………………………………………………………………………………………………………………………….ii

Lists of figures…………………………………………………………………………………………………………………………………ii

1

Introduction……………………………………………………………………………………………………………………………1

1.1

Background of the study…………………………………………………………………………………………….1

1.2

Rationale of the study………………………………………………………………………………………………..3

1.3

General objectives……………………………………………………………………………………………………..4

1.4

Specific objectives………………………………………………………………………………………………………4

1.5

Research questions…………………………………………………………………………………………………….4

1.6

Hypothesis………………………………………………………………………………………………………………….5

2

Review of literatures……………………………………………………………………………………………………………….5

2.1

General description…………………………………………………………………………………………………….5

2.2

Soil saver black oat cultivars……………………………………………………………………………………….5

2.3

Black oat as catch crops………………………………………………………………………………………………6

3

Benefits of growing catch crops………………………………………………………………………………………………6

3.1

Addition of effective soil organic matter…………………………………………………………………….7

3.2

Nitrogen mobilization……………………………………………………………………………………………….10

3.3

Phosphorus availability……………………………………………………………………………………………..12

3.4

Impacts on microbial population……………………………………………………………………………….12

3.5

Enzymatic activity……………………………………………………………………………………………………..15

3.6

Nematode control……………………………………………………………………………………………………..17

3.7

Weed management…………………………………………………………………………………………………..18

4

Methodology………………………………………………………………………………………………………………………….18

4.1

Location and climatic condition…………………………………………………………………………………..18

4.2

Determination of carbon mineralization……………………………………………………………………..19

4.3

Determination of organic carbon…………………………………………………………………………………20

4.4

Determination of microbial biomass……………………………………………………………………………20

4.5

Determination of Enzymatic activity……………………………………………………………………………21

4.6

Determination of microbial community……………………………………………………………………….21

References………………………………………………………………………………………………………………………………21

LIST OF TABLES

Table

Items Page

1

Effects of crop rotations on organic matter content of a Ferralsol (%)……………………………………8

under maize and soybean in southern Brazil

2

Biomass and dry matter yield of A. strigosa at Passo Fundo......................................................9

Brazil in different years

LIST OF FIGURES

Figures

Items Page

1

Benefits of growing cover/catch crops………………………………………………………………………………..7

2

Residual effect of winter green/cover crops on cotton yields…………………………………………….10

3

Effect of catch crops on reducing of N leaching ………………………………………………………………..11

4

Mycorrhizal roots and the associated networks of hyphae………………………………………………..13

5

Microbial biomass (C and N) under conventional tillage and……………………………………………..14 conservation agriculture affected by catch cropping

6

Shannon diversity index of soil fauna at different times during………………………………………….14

decomposition of cover plant residues in no tillage system

7

Biological and biochemical data determined in black oat ………………………………………………….16

that affected by mowing

8

Beans with black oat residues for controlling nematode………………………………………..............17

9

Scheme of an incubation jar………………………………………………………………………………………………19

1 INTRODUCTION

1.1 Background of the study

In modern sustainable agricultural systems catch crops occupy a crucial role in enhancing soil productivity under conservational and conventional tillage systems. They are grown to protect and improve the physical, chemical and biological properties of soil. These crops can be utilized for various purposes such as winter cover or green manure, supplemental forage covering periods of shortages for regular crops, living mulch, and as a catch crop. According to Lu et al. (2000), a catch crop is grown mainly to manage soil fertility, soil quality, water retention, weeds, pest, biodiversity and wildlife in an agro ecosystem which may be classified based on their taxonomic status (leguminous or non-leguminous) or growing season (winter vs. summer). Day by day fertility and quality of soil are depleted due to intensive cultivation and improper management of soil after harvesting the crops. These cause declining soil organic matter, nutrient mining, falling microbial population and activity and degraded soil structure. Soil organic matter (SOM) is the central indicator of soil quality and health, which is strongly affected by catch cropping. Effective organic matter is the part of the added organic matter that has not been one year mineralized after incorporation. Therefore, catch cropping helps to build up the soil organic matter pool within one year. In areas where the mean temperature during the winter is low and the soil often frozen, the nutrient uptake by catch crops and the decomposition of plant residues are low in the late autumn and early spring. Catch crops can be incorporated before the winter as conducted by Jensen (1991), Rasmussen and Andersen (1991) and Sorensen (1992). In heavier soils, catch crops are often incorporated before winter, but in light textured soils it is in the beginning of spring (in Belgium). Therefore, cultivation of catch crops can be the answer to restore the soil health efficiently.

Among the various catch crops, a non-leguminous cover crops with worldwide importance is black oat (Avena strigosa Schreb.) which is a cereal crop native grass species belonging to the family of Gramineae (Poaceae), family of annual herbs and monocots. Black oat has become an important winter cover crop in subtropical and temperate regions (Thomas, 2007). In USA, the commercially available ‘SoilSaver’ black oat cultivar has been released by Auburn University and USDA-ARS-NSDL in 2002 due to its efficient performance as cover crop (USDA, 2005). Black oat is the novel catch crop in the sense that its biomass production was 40-60% higher than for crimson clover and similar for rye (Schomberg et al., 2005). Biomass contributes to the primary source of soil organic matter (SOM) after incorporation into the soil while some part of the residues are responsible for releasing the N to the subsequent crops by mineralization. Immobilization of N may occur in systems with crop residue management, especially where C: N ratios of the residues are high (tough, woody materials).

Black oat is used as a catch crop to retain and recycle nitrogen which is already present in the soil. These catch crops take up surplus nitrogen remaining from fertilization of the previous crop, preventing it from being lost through leaching and tying up nitrogen in biomass, which is released back into the soil once it is incorporated as a green manure and starts to decompose (Thorup-Kristensen et al., 2003). These decomposed dry matters improve soil quality by increasing soil organic matter levels through the input of crop biomass over time which enhances soil structure, as well as the water and nutrient holding capacity of soil.

Besides the contribution of black oat as catch crop to build up the soil organic matter pool and to strengthen the prevention of N leaching, it also enhances the soil biological parameters such as microbial biomass and enzymatic activities and it alters the microbial community composition. When the residues decompose, the organic matter also encourages the formation of a rich, beneficial microbial soil "food web." According to Sullivan (2003), a rapid increase in soil microorganisms occurs after a young, relatively lush catch crop is incorporated into the soil. The soil microbes multiply to attack the freshly incorporated plant material. During microbial breakdown, nutrients originally held within the plant tissues are released and made available to the following crop. Smith et al. (2008) reported that microbial biomass was higher in the black oat cover crop plot compared to the bare plot due to decomposition of crop residues providing food to microbes; they found higher mycorrhizal (arbuscular mycorrhizal fungi) hyphae on plot where plant material was incorporated. Yang et al. (2012) found that earthworm populations increase under vegetative cover due to organic inputs favorable for growth and development. Zibilske and Makus (2009) reported that black oat cover crops significantly increased the microbial biomass and resin-extractable P where as β-glucosidase, alkaline phosphatase activities and dissolved organic carbon were found to be greater in the not mown treatment which was the indication of its potentiality in conservation tillage system. They found that standing black oat residues maintained higher levels of soil enzyme activities, controlling soil nutrient transformations and maintaining soil organic matter.

Catch crops can absorb P from both upper and lower layers of soils and transport it in their roots to subsoil layers. Again, when catch crop residues are incorporated into the soil, the crop P is released slowly and is not liable to adsorption and precipitation as inorganic P which makes it available for subsequent growing crops. Thorup-Kristensen et al. (2003) found that catch crop residues released organic acid which would help to mobilize some of the unavailable soil P. P availability by catch crops depend upon their P uptake from the soil. Therefore, the residues C: P ratio and the soil P status both determine the availability to the subsequent crop (Thibuad et al., 1988). Several studies reported that black oat has a potential to translocate of P within the rhizosphere zone (Franchini et al., 2004, Thomas, 2007). The reasons for increasing P availability in the rhizosphere zone might be the greater activity of mycorrhizal fungi which is influenced by catch cropping.

Catch crop stands often compete well with weeds during the crop growth period. It can form a nearly impenetrable mat when it is left on soil surface after terminating its growth which drastically reduces light transmittance to weed seeds and resulting lower germination rates (Teasdale, 1993). Black oat has to be found potential for controlling different weed by releasing root exudates biochemical substances through allelopathy (Price et al., 2006; Reeves et al., 2005) and these allelopathic compounds that make black oats an ideal crop for suppressing weeds.

There is a lot of evidence suggesting that black oat as a catch crop provides beneficial effect on soil health in terms of higher biomass production, increasing nutrient holding capacity, improving biological quality of soil and better weed suppression. This emphasizes the better understanding of the processes involved in black oat which should be cultivated as catch crop in order to protect the soil resource in moderate and humid climates. Therefore, it is also imperative to address how catch crops influence those soil physical attributes and soil biological activity so that black oat as catch crop management strategy can be developed that includes these criteria and promises of soil health enhancement.

In USA and Southern Brazil, they carried out many research works to appraise black oat cover crop potentiality apt as catch crop but in context of moderate and humid climate prevalent in Belgium its performance is not known to us which is our great intention at the moment.

1.2 Rationale of the study

Soil organic matter (SOM) has been unanimously acknowledged as a key factors in terms of restoring soil fertility, increasing crop productivity and ecosystem performance related to reduction of greenhouse gas emission, conserving soil biodiversity and supporting soil ecosystem health. In Europe around 45 % of mineral soils have low or very low organic carbon content and 45 % have a medium content (Rusco et al., 2001). Low levels of organic carbon usually observed in the southern Europe where about 74 % of land is covered by the soil which has less than 2 % organic carbon in top layer (0-30 cm). The low levels of organic matter are not only restricted to southern Europe but also in northern countries like Belgium some areas of low level were profound (Zdruli et al., 2004). The primary constituent of SOM is soil organic carbon (SOC). Goidts (2009) observed depletion pattern of SOC stocks in agricultural soils of southern Belgium over a long time period (1955-2005) in crop land. It was investigated that in 1955, SOC was 46.2 t C ha-1 and in 2005 it reduced to 40.6 t C ha-1 resulting in the average decrease of 5.6 t C ha-1. The decrease in application of organic manure and crop residues on cropland along with the changes of cropping pattern (progressive replacement of cereals with root crops and fodder results in a decrease of SOC stocks observed for cropland (Goidts, 2009). In the last two decades the steady decline of soil organic matter has found in Flanders and Wallonia (less than 2 % SOM) when soil was analyzed for agricultural and green manuring purposes (Gentile et al. 2009).

The decline in soil organic matter is considered to be one of major soil threats for sustainable crop production. If this decreasing pattern continues in Belgium without adopting any management practices, the SOC will be depleted that make the soil unsuitable for cultivating the crop profitably. Among the various techniques applied to conserve soil organic matter and the biological soil quality, catch cropping is one of the most important strategies for managing soil fertility and productivity to ensure sustainable crop production.

1.3 General objectives:

The main focus of the proposed research will be the restoration of soil health in terms of organic matter buildup, nutrient dynamics and soil biological activity by using black oat as catch crop in temperate and humid climate.

1.4 Specific objectives:

1. The research work will be conducted to assess the contribution of black oat as catch crop to the formation of effective soil organic matter.

2. Another important part of this proposed investigation will be focused on biological soil quality including microbial biomass, microbial community composition and enzymatic activity associated with the rhizosphere zone of black oat.

3. The research work will be further extended to determine the capacity of black oat to prevent N-leaching by N-mineralization and P-translocation within the rooting depth of black oats.

1.5 Research question

1. Does the black oat as catch crop increase the effective organic matter content compared to a control field?

2. Are the microbial biomass, microbial community composition and enzymatic activity be influenced by cultivating catch crops such as black oat?

3. Is the nutrient mobilization such as N-mineralization and P-translocation affected by the black oat catch cropping?

1.6 Hypothesis

1. At a negligible amount of effective soil organic matter can build up from the black oat residues when it used as catch crop in the prevalent climate of Flanders region.

2. A limited quantity of microbial biomass and microbial community may inhibit enzymatic activity by catch cropping of black oat in Flanders soil.

3. A limited availability of N-mineralization and P-translocation may occur within the rhizosphere zone of black oat when cultivated as catch crop in moderate and humid climate of Flanders.

2 REVIEW OF LITERATURE

2.1 General description

Black oat (Avena strigosa Schreb) is an annual cereal crop enjoying enormous popularity as a cover crop in conservation-tilled agriculture. Black oat is a species of grass native to Europe and its seeds are edible. This crop is often cultivated as animal feed in southern Brazil and sometimes reported as a weed. It has high protein content which has also been used as a high energy feed for working horses. The straw is very durable and is used for making the backs of traditional chairs (Wikipedia, 2013).

Black oat (bristle oat) was difficult to be distinguished from A. sativa in the prehistoric records. It has been grown widely until recent times as animal feed and has been eaten by people in times of famine. Few people would want to eat black oat but many had to during lean years. Black oat is still occasionally present in Scotland as a rare crop and as a relic of cultivation when it becomes a volunteer or feral. It is taller than modern oat varieties, has distinctive black grains when the plant is matured. Its grain is longer and wider than grains of other oats grown today. Planting dates are similar to common oat. If planted too early, it is more susceptible to winter chilling and lodging. Planting in late winter (early February) yielded good biomass and ground cover. Seed yields range from 800 to 1400 kg per hectare (SARE, 2007). Black oat produces large amounts of biomass, has allelopathic properties similar to common oats (can suppress weeds and crops for a few weeks) and somewhat resistant to root-knot nematode (Meloidogyne javanica) and is very resistant to rust (Prunty, 2009).

2.2 Soil saver black oats cultivar

One cultivar, SOILSAVER, was selected for increased cold tolerance and released by Auburn University and IAPAR (Institute of Agronomy of Paraná, Brazil). Auburn University and USDA-ARS researchers developed it from a population of IAPAR-61-IBIPORA, a public variety from the Institute of Agronomy of Parana, Brazil (IAPAR) and the Parananese Commission for Evaluation of Forages (CPAF). SOILSAVER black oat has several advantages as a cover crop. It tillers well, producing good soil coverage in relation to total biomass production. In weed management study of cotton (Gossypium hirsutum L.) under conservation tillage system black oat reduced weed growth with 34% compared to a fallow treatment; for rye and wheat this was 26% and 19%, respectively (SARE, 2007).

2.3 Black oat as a catch crop

In agriculture, a catch crop is a fast-growing crop that is grown simultaneously with, or between successive plantings of a main crop. Catch crops are of interest in sustainable agriculture as many of them improve the potentiality of agro-ecosystem attributes and may also indirectly improve qualities of neighboring natural ecosystems. Farmers choose to grow and manage specific catch crops based on their own needs and goals, influenced by the biological, environmental, social, cultural, and economic factors of the farming system (Snapp et al. 2005).

Leguminous cover crops are currently used worldwide and those that show potential include white lupin (Lupinus albus L.) (Mask et al. 1993; Noffsinger et al. 1998), velvet bean (Mucuna deeringiana), jackbean (Canavaliaensi formis L.), jumbie-bean (Leucaena leucocephala), wild tamarind (Lysilomal atisiliquum L.) (Caam al-Maldonado et al., 2001), crimson clover (Trifolium incarnatumL.) and other Trifolium species, and hairy vetch (Vicia villosa). Others leguminous crops play an important role in crop rotations, e.g., alfalfa (Medicago sativa L.) and soybean (Glycine max L.) but not considered as cover crops per se. Alfalfa is cultivated for forage purposes as well as for soil bioremediation and is called queen of the forages (Anonymous, 2000). Some of the non-leguminous cover crops used extensively are rye (Secale cerealeL.), wheat (Triticum aestivum L.) and oat (Avena sativa L.) (Bauer and Reeves, 1999). Other non-leguminous cover crops like black oat, white mustard (Sinapis alba L.) and rapeseed (Brassica napus L.) (Weinert et al., 2002) are grown throughout the world (Ceretta et al., 2002; Federizzi and Mundstock, 2004).

3. BENEFITS OF GROWING CATCH CROPS

Catch crops play an important role in maintaining soil quality and productivity (Figure 1). Usually we think of catch crops in terms of reducing soil erosion and adding organic matter to the soil – but they can do much more. Living catch crop mulches which can reduce the daily maximum soil temperature may have both positive (in tropical conditions) and negative (in temperate conditions) effects on main crop growth (Chassot et al. 2001). Rainfall pattern and/or water availability may be other factors that need to be taken into consideration before starting any conservation system or catch cropping. Stored soil water was found to be reduced slightly after the incorporation of winter cover crops, which necessitates proper water budgeting if planted in arid and semi-arid areas (Mitchell et al. 1999). However, the water storage capacity of the soils is increased by the incorporation of winter catch crops into soil before the next season. There are other benefits from catch crops in addition to increasing organic matter including weed control, increasing soil microbial activities, reducing soil erosion, and serving as a habitat for beneficial insects.

Figure 1. Benefits of growing cover/catch crops (Kremar, 2013).

According to USDA (2010), black oat catch crops can be applied as part of a conservation management system to support one or more of the following purposes: reduce erosion from wind and water, increase soil organic matter content, capture and recycle or redistribution of nutrients in the soil profile, increase biodiversity, weed suppression, provide supplemental forage, soil moisture management, reduce particulate emissions into the atmosphere, minimize and reduce soil compaction which increase the attention of today’s organic farming system. The importance of cultivating black oat as a catch crop in improving soil quality and soil properties has been described under the following headings.

3.1 Addition of effective soil organic matter

A soil high in organic matter is very necessary for growing crops. Little additional fertilizer would be needed if the soil has optimum (3-5%) organic matter. For profitable production fertilizer must be added where the soil contains less organic matter than this level. Greater plant productivity generally depends on higher amounts of soil organic matter. Soil organic matter accumulation is directly related to the amount of organic material added or produced to the soil versus the decomposition rate. Catch cropping is one way to increase the organic matter content over the decomposition rate. In continuously cropped soils approximately 5.43 tons per hectare per year of crop residue is considered adequate to maintain soil organic matter at the same level (Prunty, 2009). Scientists reported that soil organic matter consists of active fraction and stable fraction (effective organic matter). The active fraction represents the most easily decomposed parts of soil organic matter and consists largely of recently added fresh residues, microbial cells and the simpler waste products from microbial decay. Active fraction is responsible for the release of most N, as well as some K, P and other nutrients from organic matter into the soil (Sarrantonio, 2012).

Addition of organic matter results in improved soil structure, increased infiltration and water-holding capacity, increased cation exchange capacity (the ability of the soil to act as a short-term storage bank for positively charged plant nutrients) and more efficient long-term storage of nutrients (SARE, 2007). Effective organic matter is the part of organic matter from decomposed crop residues that is incorporated within one year and contributing to build up soil organic matter in long term. When organic material such as crop residues are added to the soil, part of it breaks down rapidly through mineralization. About half of the organic matter is soluble and releases nutrients immediately after incorporation and the rest of the part is insoluble which helps in soil organic matter enrichment (Langenberg, 2010). Vieira et al. (2004) found that among the six crops, black oat had the highest organic matter accumulation under maize and but for soybean it ranked third followed by lathyrus and lupin (Table 1) that responded to improve the soil properties.

Table 1. Effects of crop rotations on organic matter content of a Ferralsol (%) under maize and soybean in southern Brazil (Vieira et al., 2004).

Crops/Treatments

Profile depth (cm)

0-5

5-10

10-20

20-30

Means

Maize

Lupin + Black oat

4.0

3.8

4.0

4.1

4.0

Lupin

3.7

3.7

3.5

3.8

3.7

Rye

3.9

3.6

3.9

3.5

3.8

Oat

3.6

3.8

3.9

3.6

3.7

Lathyrus

3.8

4.0

4.2

4.1

4.0

Wheat

3.7

3.7

3.9

3.7

3.8

Crotalaria

3.7

3.8

3.8

3.8

3.8

Black oat

4.1

3.9

4.1

3.7

4.0

LSD(0.05): Trts (T)

0.10

Depth (D)

0.42

T × D

0.22

Soybean

Lupin + Black oat

3.6

4.1

3.9

3.8

4.0

Lupin

4.3

4.2

3.9

3.9

4.1

Rye

4.0

4.1

3.9

3.7

3.9

Oat

4.1

4.2

4.1

3.8

4.1

Lathyrus

4.2

4.8

4.1

3.5

4.2

Wheat

4.1

3.7

3.8

3.5

3.8

Crotalaria

4.0

3.9

3.9

3.6

3.9

Black oat

3.9

4.1

4.0

4.1

4.0

LSD(0.05): Trts (T)

0.31

Depth (D)

0.83

T × D

0.50

According to Valenzuela and Smith (2002), black oat is good for increasing soil organic matter content to improve soil structure under animal grazing systems which provided long lasting residues for a following crop. It has the enormous potentiality to produce a considerable amount of biomass in comparison with other non-leguminous or leguminous cover crops. Zibilske and Makus (2009) found that the biomass production capacity was 4.37 t ha−1 after complete desiccation of the standing black oat crop. In addition to that, it has many desirable qualities over the other cover crops. In a study conducted by Schomberg et al. (2005) results showed that the biomass production and soil N mineralization dynamics of black oat was similar to crimson clover, indicating the potential of black oat as a catch crop.

Black oat can produce a comparable dry matter yield to that of rye grass (Lolium perenne L.) and it can also thrive well with other legume forage crops like barrel medic (Medicago truncatula L.) (Lowe and Bowdler, 1998) in USA. Black oat reached maximum biomass at anthesis (8579 kg ha-1), while rye (Secale cerealeL.) and wheat (Triticum aestivum L.) continued to increase biomass significantly through soft dough (9497 kg ha-1 and 10460 kg ha-1, respectively) (Ashford and Reeves, 2003). Therefore, black oat can be terminated at an earlier stage compared to the other two cover crops. Early termination of black oat perhaps reduces depletion of the available nutrients and moisture in the field. This is a useful trait since it can be planted as a fall-sown winter catch crop. Since black oat has the C3 photosynthetic pathway for Carbon fixation (Tesar, 1984), it can contain more available NH4+ per dry matter mass unit compared to C4 cover crops such as Pennisetum glaucum, Sorghum vulgare and Brachiaria decumbens (Rosolem, 2005). Even though black oat can thrive well in mixed culture with wheat but performs poorer than in monoculture in terms of biomass production (Cousens et al. 2003). According to EMBRAPA (2004), black oat has a good amount of crop residues and C: N ratio that helps in soil particles aggregation.

Table 2. Biomass and dry matter yield of A. strigosa at Passo Fundo, Brazil in different years (Floss, 2001).

Year

Green biomass

Dry matter

(kg ha-1)

(kg ha-1)

1991

32 568

8 550

1992

33 088

8 002

1993

22 409

5 214

1994

20 182

5 500

1995

20 064

5 385

1996

28 293

7 509

1997

26 630

6 657

1998

27 386

6 018

1999

36 202

7 402

In Brazil data obtained by Floss (2001) over a ten-year period at Passo Fundo (RS) with A. strigosa (average of several genotypes every year) (Table 2) shows the usual variation among years normal in the subtropical environment, with years of excellent development in terms of green biomass and dry matter production. FAO (2004) reported that the dry matter production (6808 kg ha-1) of black oat was higher than white oats (4604 kg ha-1) which suggested that more biomass was added to the soil.

Again, after incorporation of fresh black oat residues as green manure developed good biomass that left an excellent soil cover and provides the sources of essential nutrients which in turn increased the cotton yields (Figure 2). Among various covers crops, black oat stands second which ensured its potentially to be grown as catch crop.

Figure 2. Residual effect of winter green/cover crops on cotton yields. Chore Experimental Station. Average of three years agricultural years (1996/97, 1997/98 and 1998/99). Florentin, 1999 (unpublished).

3.2 Nitrogen mobilization

Nitrogen present or added to the soil is subjected to several changes (transformations) that dictate the availability of N to plants and influence the potential movement of NO3- to water supplies. Organic N that is present in SOM, crop residues and manure is converted to inorganic N through the process of mineralization. Availability of C and N in decomposing residues and soil organic matter influences the mineralization– immobilization process and the amount of N available to subsequent crops (Hadas et al. 2004). Bauer and Reeves (1999) found that cotton (Gossypium hirsutum L.) yields were higher following black oat than rye on a coastal plain soil in South Carolina, USA. More cotton yield following black oat may have been due to higher N availability. Thorup-Kristensen et al. (2003) reported that catch crops are grown to catch N from soil which prevent leaching of N to the environment (Figure 3)

Figure 3 Effect of catch crops on reducing of N leaching. It is clearly seen that the reduction of leaching is occurred with catch cropping. [data from the experiment of Olesen et al. (2000)].

Nitrate leaching from the soil is a crucial problem for water sources near the agricultural fields (Sainju and Singh, 2001). One of the methods to control nitrate leaching from the crop field is to plant a catch crop with an extensive root system that can translocate the available nitrogen into their biomass. Thorup-Kristensen et al. (2003) found that catch crop removed N from the soil and before the catch crop killed soil N level remained low which increased N for the subsequent crops just after incorporation of residues. The effect of a catch crop on N supply for the succeeding crop is the combined effect of the N depletion made before catch crop incorporation and the N release due to mineralisation after incorporation (Thorup-Kristensen, 1993; Thorup-Kristensen and Nielsen, 1998). In a study conducted by Schomberg et al. (2005) results showed that the biomass production and soil N mineralization dynamics of black oat were similar to those of crimson clover, indicating the potential of black oat as a cover crop in a subtropical and humid climate and the amount of N mineralized in 90 days measured with in situ soil cores was 1.3 to 2.2 times greater following black oat, crimson clover, and oilseed radish than following rye.

So the catch crop especially the black oat has the potential to capture this nitrate through its root system and release N during the decomposition of residues which makes the further crop cultivation beneficial.

3.3 Phosphorus availability

In natural ecosystems on young, little weathered soils, P availability is controlled by the dissolution of primary mineral phosphate (Tiessen et al. 1984). However, in more weathered soils, the decomposition and mineralization of forest litter and soil organic matter come to be the primary sources of P, since mineral P is retained mostly in less available forms (Vincent et al. 2010). In the conversion of natural ecosystems to agricultural areas, the native plants, well-adapted to low levels of available P are substituted by crops with high nutrient requirements, with lower capacity and strategies for P uptake and use. Therefore, in view of the crop demand these environments are generally P-deficient, which limits yields and requires phosphate supply by fertilization.

Black oat produced large amounts of dry matter from 1996 to 2005; over the course of the 10 years in which all winter species were grown, black oat accumulated 15 Mg ha-1 of residues during the 10 years period than the other cultivated species (Calegari, 2006). These residues probably cycled a larger amount of P, resulting in the higher content of labile P forms in soil surface layers under no tillage system. Tiecher et al. (2012) found that black oat and blue lupin were the most efficient P-recyclers and under no tillage, they increased the labile P content in the soil surface layers.

Thomas (2007) reported that Pea (Pisum sativum L. subsp. arvense), black oat and narrow leafed lupin (Lupinus angustifolius L.) were the most efficient cover crops for translocation of soil phosphorus for a 0 to 55 cm depth in oxisol soils. Black oat had higher root phosphorus content with P-fertilizer application. This is due to the fact that black oats can absorb phosphorus from soil using specialized proteoid roots. These cluster roots release citric acid to mobilize the sparingly available P in the rhizosphere (Neumann et al. 1999).

White lupin has the highest capacity of P accumulation in the aerial parts without P application. In the presence of P fertilizer, black oat accumulated more than 20 kg ha-1 P-content on the aerial parts whereas without P application black oat had the highest root dry matter content among the ten cover crops (Avena strigosa, Avena sativa, Secale cereale, Pisum sativum sub sparvense, Pisum sativum, Vicia villosa, Vicia sativa, Lupinus angustifolius L., Lupinus albus, and Triticum aestivum) studied (Franchini et al. 2004).

3.4 Impacts on the microbial community

Soil microbial dynamics is one of the most important aspects in terms of measuring the biological quality of soil which is influenced by catch cropping. Scientists reported that soil organic matter consists of active fraction and stable fraction (effective organic matter). The active fraction represents the most easily decomposed parts of soil organic matter and consists largely of recently added fresh residues, microbial cells and the simpler waste products from microbial decay. Active fraction is responsible for the release of most N, as well as some K, P and other nutrients from organic matter into the soil (Sarrantonio, 2012).

Catch crops encourage populations of beneficial fungi and other microorganisms that help to bind soil aggregates. The fungi, called mycorrhizae produce a water-insoluble protein known as glomalin, which catches and glues together particles of organic matter, plant cells, bacteria and other fungi (Wright and Upadhaya, 1998). Glomalin may be one of the most important substances in promoting and stabilizing soil aggregates (Sarrantonio, 2012).

Catch crops roots develop beneficial mycorrhizal relationships. The hyphae are the root like extensions of fungus that take up water and soil nutrients to help nourish plants. In low-phosphorus soils, for example, the hyphae can increase the amount of phosphorus that plants obtain. The hyphae are intercellular and intracellular to go through into the plant roots (Figure 4).

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Figure 4. Mycorrhizal roots and the associated networks of hyphae are a major component of most soils (FAO, 2013)

Soil micro-organisms are of great importance for plant nutrition as they interact directly in the biogeochemical cycles of the nutrients. Increased crop biomass by incorporating catch crops increases the food sources for the microbial population in the soil which stimulate the development and activity of soil micro-organisms. In one 19-year experiment in Brazil, such practices resulted in a 129% increase in microbial carbon biomass and a 48% increase in microbial N biomass (Figure 5). Therefore our concern is how much the black oats residues can encourage microbial response by growing a catch crop. The figure shows that in conservation tillage system growing catch crops enhanced total organic carbon and nitrogen from the microbial biomass.

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Figure 5. Microbial biomass (C and N) under conventional tillage and conservation agriculture affected by catch cropping (Balota, Andrade and ColozziFilho, 1996).

Figure 6. Shannon diversity index of soil fauna at different times during decomposition of cover plant residues in no tillage system. Error bars represent the standard error around each treatment mean (Gatiboni et al., 2011.)

Soil microbes help in decomposition of plant residues that is governed by biological process. Gatiboni et al. (2011) found that black oat residues had a great potential to attract more soil fauna which was represented by using the Shannon index (Figure 6). Shannon index commonly used to characterize species diversity in a community that accounts for both abundance and evenness of the species present. Among the three crops like rye, black oat and common vetch, the black oat was positioned as second just after rye which also fostered the decomposition rate as well as release of nutrient and addition of soil organic matter.

3.5 Enzymatic activity

Besides increasing microbial biomass, black oat as cover crops enhanced the activity of enzyme which has been represented in Zibilske and Makus (2009) findings. Total inorganic nitrogen, dissolved organic carbon, extractable resin phosphate, alkaline phosphate activity and β-glucosidase activity were found enhanced by black oat catch cropping (Figure 7). Microbial biomass was increased significantly with the attaining of maturity which was negatively correlated with soil inorganic nitrogen (Figure 7a & 7b). The significant decrease in inorganic N over time can be explained by immobilization of N into the microbial biomass. The dissolved organic carbon found decreased in middle period might be due to extremely precipitation whereas higher in the last time (Figure 7c). Resin extractable P (Figure 7d) had been relatively steady over the first two sampling periods, but increased significantly (P=0.037) at the last.

As alkaline phosphatase activity decreases (Figure 7e) overtime, microbial biomass increases (Figure 7a), suggesting that P availability for microbial biomass growth is adequate as decomposition proceeds over time. Phosphorus sources for this biomass increase may be native P forms (mostly precipitated forms in the calcareous soil) or organic P contained in the black oat roots and residues. McCallister et al. (2002) concluded that soil phosphatase activity may not accurately predict P supply for crop production.

β-glucosidase activity (Figure 7f) was significantly (P=0.015) higher in the not mown treatment at all times. Cellulase enzyme activities have been reported to be related to season (Pavel et al., 2004). Decomposition of roots must be forceful to β-glucosidase activity which is the most accessible tissue to soil microorganisms in that case. Some cellulase complex enzymes reportedly respond more to organic matter additions and β-glucosidase activity between treatments, and over time, were responding to changes in overall carbon availability in the system.

Microbial biomass C (active fractions of soil organic carbon) and β-glucosidase have been reported to be a more sensitive and an important component of soil P cycling has been found from phosphatase activity that provides an indicator of a soil's capacity to mineralize P by black oat catch cropping (Bandick and Dick, 1999; Dick et al. 1996; Schutter and Dick, 2002).

Figure 7. Biological and biochemical data determined at three times in the three mowing treatments. (a) microbial biomass (b) total inorganic N (c) dissolved organic C (d) resin-extractable phosphate-P (e) soil alkaline phosphatase and (f) soil β-glucosidase. Bar = Standard Error of the Mean (SEM), n=3, Pb0.05. (Source: Zibliske and Makus, 2009).

3.6 Nematode control

Black oats as mixed crops can be grown to protect the crops from the devastating effects of plant parasitic nematodes. Plant parasitic nematodes feed on plant roots resulting in yellowing, wilting, stunting and finally caused yield reduction which is the direct feeding damage. In addition, invasion by plant-parasitic nematodes often provides an infection route for other organisms such as bacteria or fungi. Nematode reproduces very fastly although their population is less at the beginning of the season. Response of nematodes is greatly influenced by the cultivar of a crop plant species. Kruegerand McSorley (2012) found that catch cropping is one of the most effective ways of managing root knot nematode in the crop field (Potter et al. 1998, Vargas-Ayala et al. 2000).

Figure 8. Beans with black oat residues (www.ars.usda.gov/msa/auburn/nsdl)

According to USDA (2010), black oat provides excellent nematode control especially the root knot nematode (Figure 8). Gomes et al. (2010) found that black oat suppressed the Mesocricone maxenoplax in the field when growing as cover crops pre-planting peach cultivation and were found unfavourable host for nematode reproduction. In a greenhouse study of 17 plant species suitable for use as cover crops, black oat was shown to be resistant to root-knot nematode Meloidogyne javanica (USDA, 2005). In Brazil study conducted using five cultivars of black oat demonstrated that all of them are resistant to Meloidogyne incognita and M. paranaensis (Moritz et al. 2003). Black oat is also non host for Pratylenchus penetrans as Meloidogyne hapla and therefore good to grow as green manure.

3.7 Weed management

Black oat provides excellent weed control; particularly against broadleaf weeds due to prolific tillering habit that gives good ground coverage and suppresses weeds. It can inhibit the weeds cut leaf evening primrose (Oenother alaciniata H.) and common chickweed (Stellaria media L.) (Reeves et al. 2005). Saini et al. (2005) reported 40% weed biomass reduction in cotton planted in black oat due to sod covering the surface. Without herbicides, black oat gave greater sickle pod (Sennaobt usifolia L.) and palmer amaranth control than rye or wheat, showing the suitability of black oat as an effective cover crop for weed suppression (Patterson et al., 1996).

Thomas (2007) found the allelopathic activity of black oat from eighteen accessions collected from different regions by using bio-assay and accession CIav 2520 showed the most radicle suppressive ability among all accession studied which is an indication of the effectiveness of black oat in suppressing weed growth in real crop field. These results also agreed by Miyazawa et al. (2002) and Caamal-Maldonado et al. (2001)

4. METHODOLOGY

4.1 Location and climatic condition

The experiment will be conducted in two locations in Flanders, the northern region of Belgium: one heavy textured soil (clay or loam) and one light textured soil (sand or sandy loam). The climate prevails in the experimental site with a daily average temperature of 10. 54° C, the average daily relative humidity is 79.97 % and average monthly and annual precipitation is 71.03 mm and 852.4 mm, respectively.

Sampling

On each location, 2 fields with similar history and similar rotations will be selected, one with the frequent use of black oat and one without (another catch crop such as white mustard is possible). Sampling will be done at four moments: late summer, autumn, late winter and in spring. Each time, the 4 fields will be sampled cross-wise (+/- 15 sample points/ha) for the 0-30 cm layer.

Parameters to be determined: Initially late summer:

Soil OC/OM content,

Soil pH,

Soil total N content,

Texture,

Soil bulk density,

pF curves and

C-mineralization rate of the soil organic matter (0-30 cm),

At every sampling moments: microbial biomass content (C and N), enzymatic activity (dehydrogenase/β-glucosidase), microbial community composition (PLFA), total P, available P and mineral N (biological parameters: 0-30 cm; P and N: 0-30, 30-60 and 60-90 cm depth)

Replication: each parameter will be replicated for four times.

4.2 Determination of carbon mineralization

Carbon mineralization will be assessed during an aerobic incubation experiment. Two hundred grams of air-dried, homogeneously mixed and 2-mm sieved soil will be placed in PVC tubes (diameter of 6.8 cm and 7 cm height) and water should be added to an equivalent of 50% water filled space. The soil columns will be placed inside of sealed glass jars with an inner diameter of approximately 0.1 m, as shown in figure 9.

mineralization

Figure 9 Scheme of an incubation jar

Small vials containing 15 ml 1 M NaOH solution will be placed in the air-tight seals jars to trap CO2 evolved from the soils which incubate at room temperature (21.7°C) for 16-19 weeks. SOM decomposition will be monitored during incubation period through timely determination of the CO2 trapped in the NaOH. The excess NaOH will be back-titrated with standard 1M HCl after precipitating the carbonates with 2 ml 0.5M BaCl2 (Anderson, 1982). The following reaction takes place when the NaOH-solution is titrated: 2 NaOH + CO 2  Na 2CO 3 + H2O. The amount CO2-C released from the soil by the formula:Where, CO2-C: CO2-C released during mineralisation (mg), C: HCl added to control (ml), S: HCl added to sample (ml), M: exact molarity of NaOH and 6: conversion factor (1 ml 1 M HCl = 6 mg CO2-C)

A parallel first- and zero-order kinetic model will be used to describe observed C mineralization in soil.. The incubations will be carried out with an average temperature of 21.7°C, but mineralization rates for field conditions are more telling. Therefore, kopt;WFPS estimates will be converted to the mean annual temperature in Belgium, 9.7°C, using a S-shaped function proposed by De Neve et al. (1996)., where, T the temperature (°C), kopt;T the C mineralization rate at Topt, the optimal temperature (37 °C), and κ (2.55) a rate parameter reflecting the temperature sensitivity of k. kopt-values will be found by introduction of k estimates at 21.7 °C in the left term of equation and T = 21.7 °C in the right term. Substitution of kopt and T=9.7°C will give the C mineralization rate under field conditions.

4.3 Determination of organic carbon

Walkley & Black (1934) method is used for soils containing less than 10 % organic carbon. The principle is that a weighed amount of soil is mixed with an oxidant. Part of the oxidizing agent will be reduced by oxidizing the organic matter. The remaining amount of oxidant is measured by titration.

Reaction: 2K2Cr2O7 + 3C + 8H2SO4  2K2SO4 + 2Cr2(SO4)3 + 3CO2 + 8H2O

4(Cr6+ + 3 e  Cr3+)

3(C - 4 e  C4+)

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4Cr6+ + 3 C  4Cr3+ + 3C4+

The following formula can be used to determine % C:

Where a = added FeSO4 to the blank solution (=without soil sample), b = added FeSO4 to the sample. When, b=0 or the difference (a-b) = a then 10 ml K2Cr2O7 is reduced and, in theory, 30 mg C is oxidized.

Then, 1 g the air-dried soil contains:

4.4 Determination of microbial biomass

Fumigation extraction method is used to determine the microbial biomass (Voroney et al., 1993). In this method, two petridishes with 30 g fresh soil should be kept in desiccators with 50 ml ethanol-free chloroform (+ boiling chips) and moistened tissue which is closed by tap and covered by black plastic. Air will be evacuated until chloroform boils for 10 to 15 minutes. The dessicators need to open to remove the chloroform tissue and then the sample becomes ready for extraction. Fumigated sample will be kept in erlenmeyer flask and 60 ml 0.5 M K2SO4 need to be added which will be shaked for 1 hr. Extracts will be filtered using Whatman nr. 5 filter paper and filtrates may be stored in the freezer (-18 °C) until analysis.

4.5 Determination of Enzymatic activity

β-glucosidase and dehydrogenase activity will be determined following K. Alef & P. Nannipieri method and concentration will find out using calibration curve.

4.6 Analysis of soil microbial community composition

PLFA method will be applied to find out the microbial community composition which determining relative distribution of functional groups of phospholipid fatty acid.