Legume Green Manure Research Articles

Biomass yields, soil cover, content and accumulation of nutrients of some green manure legumes grown under conditions of north of Minas Gerais, Brazil.

The potential of green manure crops as conservation practice play an important role in soil quality and sustainability of agricultural systems. This field experiment was conducted in 2009 season to evaluate the performance of different green manures cultivated under Minas Gerais conditions, southeast Brazil. The treatments, in randomized blocks with three replications, were: Spontaneous vegetation (control), Sunhemp (Crotalaria juncea), Pigeonpea (Cajanus cajan), Velvetbeans (Mucuna aterrima, Mucuna pruriens, Mucuna deeringiana), Lablab (Lablab purpureus), Jackbean (Canavalia ensiformis), Cowpea (Vigna unguiculata) and mixture (all treatments). From the green manures screened, M. pruriens and the spontaneous vegetation presented the highest soil covering potential. The largest productions of fresh shoot biomass were recorded from the spontaneous vegetation, C. juncea and C. ensiformis. C. juncea and spontaneous vegetation also had the largest production of dry shoot biomass. The green manures presenting more nutrients in the shoot were the C. juncea, with higher contents of N, P, Ca, Mg and B, and spontaneous vegetation with the highest contents of K and Mg. In conclusion, the use of these green manures is promising and an appropriate technology for the reduction of chemical fertilizer use. Key words: Agroecology, Canavalia ensiformis, crop rotation, family farming, green manures.

Nine-year results on maize and processing tomato cultivation in an organic and in a conventional low input cropping system

Nine-year results on yields and apparent balances of organic matter and nitrogen (N) are reported for maize and processing tomato cultivated in a long term comparison trial between an organic and a conventional low-input system in Central Italy. In every year, above ground biomass and N accumulation of each cash crop and green manure, including weeds, and the partitioning between marketable yield and crop residues were determined. Apparent dry matter and nitrogen balances were calculated at the end of each crop cycle by taking into account the amounts of dry matter and ex-novo N supplied to the system as green manure legume Ndfa (i.e. an estimate of N derived from the atmosphere via symbiotic fixation) and fertilizers, and those removed with marketable yield. Processing tomato complied with organic cultivation better than maize. As compared to the conventional crop cultivation, organic tomato provided similar yields, used supplied N more efficiently and left lower residual N after harvest, with lower related risks of pollution. Organic maize yielded less than conventional one. The main limitation for organic maize was the low N availability during initial growth phases, due to either low N supply or low rate of N release from incorporated green manure biomass. In both organic and conventional cultivation the system sustainability could be improved by an appropriate crop rotation: wheat in fall winter likely prevented leaching loss of mineral N in both systems; green manure crops in the organic system allowed to either trap and recycle soil mineral N or supply ex novo legume Ndfa to the soil, with benefits in mitigation of N pollution and improvement in self-sufficiency of the system.

Nitrogen fixation by pea and lentil green manures in a semi-arid agroecoregion: effect of planting and termination timing

Crop-fallow systems dominate many semi-arid agricultural regions despite fallow’s negative effects on soil and water quality. Annual legumes grown as a fallow-replacement crop, and terminated prior to maturity, can reduce these negative effects without substantially decreasing plant available water for the subsequent crop. Interest in growing legume green manures (LGMs) in synthetically-fertilized systems is increasing in the northern Great Plains of North America, partly due to the N-fixing capabilities of legumes; however, little is known about the effects of planting and termination time on N fixation amounts in the region. A 2-year field study was initiated in southwest Montana to determine the effects of planting time (spring or summer) and termination time (e.g. flower or pod) on the amount of N fixed by field pea (Pisum sativum cv. Arvika) and lentil (Lens culinaris cv. Richlea). Two methods, 15N natural abundance and N difference, were used to quantify N fixation, with wheat or in-crop weeds as reference plants. In 2009, N fixed by spring-planted lentil was higher by pod than flower (P = 0.03). Termination time did not affect the amount of N fixed by spring-planted pea, despite more biomass by pod than flower. In 2010, both spring-planted crops fixed more N by pod than flower (P < 0.01) and more N was fixed by spring-planted than summer-planted crops (P < 0.01). These results should prove useful to growers interested in selecting management practices that optimize N fixation of LGMs.

Long-term effects of crop rotations and fertilization on soil C and N in a thin Black Chernozem in southeastern Saskatchewan

Lemke, R. L., VandenBygaart, A. J., Campbell, C. A., Lafond, G. P., McConkey, B. G. and Grant, B. 2012. Long-term effects of crop rotations and fertilization on soil C and N in a thin Black Chernozem in southeastern Saskatchewan. Can. J. Soil Sci. 92: 449–461. Carbon sequestration in soil is important due to its influence on soil fertility and its impact on the greenhouse gas (GHG) phenomenon. Carbon sequestration is influenced by agronomic factors, but to what extent is still being studied. Long-term agronomic studies provide one of the best means of making such assessments. In this paper we discuss and quantify the effect of cropping frequency, fertilization, legume green manure (LGM) and hay crops in rotations, and tillage on soil organic carbon (SOC) changes in a thin Black Chernozemic fine-textured soil in southeastern Saskatchewan. This was based on a 50-yr (1958–2007) crop rotation experiment which was initiated on land that had previously been in fallow-wheat (Triticum aestivum L.) (F-W), or F-W-W receiving minimum fertilizer for the previous 50 yr. We sampled soil in 1987, 1996 (6 yr after changing from conventional tillage to no-tillage management and increasing N rates markedly) and again in 2007. The SOC (0–15 cm depth) in unfertilized F-W and F-W-W appears not to have changed from the assumed starting level, even after 20 yr of no-till, but SOC in unfertilized continuous wheat (Cont W) increased slightly [not significant (P&gt;0.05)] in 30 yr, but increased more after 20 yr of no-till (but still not significant). No-till plus proper fertilization for 20 yr increased the SOC of F-W, F-W-W and Cont W in direct proportion to cropping frequency. The SOC in the LGM-W-W (unfertilized) system was higher than unfertilized F-W-W in 1987, but 20 yr of no-tillage had no effect, likely because grain yields and C inputs were depressed by inadequate available P. Soil organic carbon in the two aggrading systems [Cont W (N+P) and F-W-W-hay(H)-H-H (unfertilized)] increased significantly (P&lt;0.05) in the first 30 yr; however, a further 20 yr of no-tillage (and increased N in the case of the Cont W) did not increase SOC suggesting that the SOC had reached a steady-state for this soil and management system. The Campbell model effectively simulated SOC changes except for Cont W(N+P), which it overestimated because the model is ineffective in simulating SOC in very fertile systems. After 50 yr, efficiency of conversion of residue C inputs to SOC was negligible for unfertilized F-W and F-W-W, was 3 to 4% for fertilized fallow-containing systems, was about 6 or 7% for Cont W, and about 11% for the unfertilized F-W-W-H-H-H systems.

Long-term effects of crop rotations and fertilization on soil C and N in a thin Black Chernozem in southeastern Saskatchewan

Lemke, R. L., VandenBygaart, A. J., Campbell, C. A., Lafond, G. P., McConkey, B. G. and Grant, B. 2012. Long-term effects of crop rotations and fertilization on soil C and N in a thin Black Chernozem in southeastern Saskatchewan. Can. J. Soil Sci. 92: 449-461. Carbon sequestration in soil is important due to its influence on soil fertility and its impact on the greenhouse gas (GHG) phenomenon. Carbon sequestration is influenced by agronomic factors, but to what extent is still being studied. Long-term agronomic studies provide one of the best means of making such assessments. In this paper we discuss and quantify the effect of cropping frequency, fertilization, legume green manure (LGM) and hay crops in rotations, and tillage on soil organic carbon (SOC) changes in a thin Black Chernozemic fine-textured soil in southeastern Saskatchewan. This was based on a 50-yr (1958-2007) crop rotation experiment which was initiated on land that had previously been in fallow-wheat (Triticum aestivum L.) (F-W), or F-W-W...

Influence of no-tillage and frequency of a green manure legume in crop rotations for balancing N outputs and preserving soil organic C stocks

The sustainability of crop production systems depends on the adoption of practices that allow the balancing of nutrient output and the preservation of soil organic matter. In Brazil, no-tillage (NT) is widely adopted for soybean-based cropping systems. In the Southern region, soybean alternates with maize in the summer and black-oats or wheat in the winter. Green-manure legumes are occasionally introduced in the crop rotation to break the continuous use of wheat in the winter. The objective of the present study was to evaluate if NT adoption would increase biological nitrogen fixation to soybean and other legumes. The hypothesis that a system richer in N would bring about positive effects on soil C stocks, was also tested. The study was carried out in Londrina, Paraná State, in Southern Brazil on a clayey Ferralsol that was cropped under NT with soybean as the main crop for more than 25 years. In 1997, three different crop rotations under both NT and conventional plough tillage (CT) were introduced. The crop rotations were composed of soybean, maize, wheat, black-oats and white lupins, but differed from each other in the frequency that each crop appeared in the rotation. Crop yields and the biomass of lupins and black-oats were quantified at every harvest during the 12 years of this study. Conversion factors of measured yield and biomass into C and biologically fixed N inputs to the crop system were developed from whole plant measurements performed in four of the twelve years of the study. The contribution of biological N2 fixation (BNF) to the legumes was determined using the ureide abundance and the 15N natural abundance techniques in 1998, 1999, 2005 and 2007. From these data, the calculation of N balance for each rotation (input N minus output N in harvested grain) was carried out. Soil C and N stocks to 80cm depth were quantified in 1997, 2003 and 2009. Grain yields were higher under NT for soybean and under CT for maize, in the rotation with the lowest frequency of legume crops. Soybean reliance on BNF was higher under NT (76%) than under CT (68%) whilst for lupins the reliance was 68% under NT and 60% under CT. The use of lupins as a green manure represented an extra contribution to soil N of approximately 300kgNha−1 and this was essential to maintain a positive N balance for the system. The comparison of soil C stocks between 1997 and 2009 revealed almost no gain in soil C under NT, but a C loss of 19MgCha−1 after 12 years of CT. Significant soil C and N losses were recorded in the rotation where lupins were planted more frequently and fertilizer N application to maize was suspended, which resulted in a very negative N balance for the system. The results highlight the importance of NT to enhance BNF inputs to the system and the need to recognize the N balance as a key driver of C stock changes in the soil. In addition, it suggests NT in this study had the consequence of avoiding soil C loss rather than increasing soil C stocks.

녹비작물 이용 유기벼 재배지의 논잡초 발생과 벼 수량

The use of green manure crop is one of the methods for alternative of chemical fertilizer as well as maintain of soil sustainability, therefore we evaluated the effect of green manure crops on rice growth and weed occurrence in rice-green manure crop double cropping system. The treatments consisted of incorporation of hairy vetch, barley or combined hairy vetch and barley without any agrochemical or fertilizer. In hand weeding, rice yield in hairy vetch only or hairy vetch and barley incorporated fields was attained by 90% and 93% of the conventional practice, respectively, while the value in barley incorporated fields was just 79%. Although the rice yields were lower than the hand weed control, similar trends in non-weed control were observed among all treatments. At maximum tillering stage, occurred weeds in hairy vetch, barley or hairy vetch and barley incorporated fields were five, five and two species, respectively, while those in conventional practice were six species. Also, the dry weight of weeds in hairy vetch and barley incorporated fields was decreased by 33% and 53% compared to it of conventional practice, while the value in hairy vetch and barley incorporated field was increased by 34%. Among all treatments, although occurrence density of Echinochloa crus-galli was lower than another weed species, the dry weight of it significantly increased. These results suggested that although continuous incorporation of proper amount of legume green manure crops was possible to productivit y insurance of crop, but to attain it was essential to the effective management of weeds.

Use of legume green manures as nitrogen sources for corn production

AbstractRecent volatility in supplies and prices of natural gas and synthetic nitrogen (N) fertilizer suggests a need to develop and refine alternative strategies for supplying N to corn. In this study, conducted in north-eastern Iowa, we examined the use of red clover and alfalfa green manures as means of supplying N to a succeeding corn crop. Red clover intercropped with oat produced significantly more biomass and contained more N than alfalfa intercropped with oat. Tilling green manures in the fall or delaying tillage until the following spring did not have a consistent effect on green manure N content. Without N fertilizer, corn grain yield following oat–red clover and oat–alfalfa was 25–63% greater than following oat grown alone, but at the highest fertilizer rate (202 kg N ha−1), there was no difference in corn yield between oat–legume and oat-alone treatments. These patterns support the premise that legume green manure effects on corn yield were N-related. Red clover green manure had an N fertilizer replacement value for corn of 87–184 kg N ha−1; alfalfa supplied corn with the equivalent of 70–121 kg N ha−1. At a fossil energy cost for N fertilizer of 57 MJ kg−1N, reducing synthetic N fertilizer applications to corn by 70–184 kg N ha−1would represent a fossil fuel savings of 3990–10,488 MJ ha−1, equivalent to the energy content of 104–274 m3of natural gas. These types of savings are likely to become increasingly important as fossil energy supplies become scarcer and fertilizer prices rise.

Tillage and green manure effects on Bt transgenic cotton ( Gossypium hirsutum L.) hybrid grown on rainfed Vertisols of central India

Transgenic Bt cotton hybrids, in India, now constitute more than 90% of the cotton area. Conservation tillage systems such as reduced tillage (RT) improve soil health and crop productivity. Field experiments were conducted to study the response of Bt cotton hybrids to the tillage methods in a split plot design for three years (2005–2006 to 2007–2008) with tillage practices as main plots (conventional tillage {CT}, RT with two inter-row cultivations {RT 1} and RT with no inter-row cultivation {RT 2}). In the sub-plot, in situ green manure (GM) was included along with 100 (GM + N 100), 80 (GM + N 80) and 60 kg N ha −1 (GM + N 60) and were compared to N alone (N 100). Growth, yield and fibre quality of Bt transgenic cotton hybrid (RCH-2 Bt) were monitored during the study. In all seasons, weed density and biomass were significantly lower in the RT treatments than in the CT treatments. Taller plants with more main stem nodes were produced on the RT plots (63.6–75.8 cm) than on the CT plots (58.1–70.2 cm). Thus, plants of RT treatment retained more bolls (60.8–62.0 m −2) than those of the CT treatment (52.4 m −2). Averaged over seasons, RT treatment had seed cotton yield (1717–1740 kg ha −1) significantly higher than the CT treatment (1489 kg ha −1). The treatments N 100, GM + N 100 and GM + N 80 (1687–1734 kg ha −1) did not differ and were significantly better than the GM + N 60 (1303 kg ha −1). Tillage × GM interaction was significant in two of three years and data combined over years. The RT plots with GM had significantly greater yield than the CT plots. Compared to the CT treatment, the RT plots had significantly greater proportion of water stable aggregates (48.6% vs. 54.4–56.0%) and mean weight diameter (0.47 mm vs. 0.49–0.51 mm). The GM plots had significantly higher WSA and MWD than those without. Further, soil moisture content was greater in the GM mulched plots up to 0.60 m depth compared to without GM treatment (CT + N 100). Favourable soil physical properties may have contributed to improved seed cotton yield in the RT treatments with GM than in the CT treatment. Fibre quality was not affected by either the tillage systems or GM. This study indicates that Bt transgenic cotton can be grown under RT systems with an in situ legume GM.

Effect of crop rotation, fertilizer and tillage management on spring wheat grain yield and N and P content in a thin Black Chernozem: A long-term study

Campbell, C. A., Lafond, G. P., VandenBygaart, A. J., Zentner, R. P., Lemke, R., May, W. E. and Holzapfel, C. B. 2011. Effect of crop rotation, fertilizer and tillage management on spring wheat grain yield and N and P content in a thin Black Chernozem: A long-term study. Can. J. Plant Sci. 91: 467–483. We analyzed the agronomic data from a 50-yr crop rotation experiment being conducted on a fine-textured, thin Black Chernozem at Indian Head, Saskatchewan in Canada. Our objective was to determine how a change from conventional-till to no-till, together with an increase in N fertilizer rates recommended by the Saskatchewan Soil Testing Laboratory has affected wheat yields and N and P balance in the systems over the past 20 yr. The treatments assessed were fertilized (N+P) and unfertilized fallow-wheat (Triticum aestivum L.) (F-W), F-W-W, and continuous wheat (ContW), and unfertilized legume green manure (LGM)-W-W and F-W-W-brome (Bromus inermis Leyss.)/alfalfa (Medicago sativa L.) hay (H)-H-H. On average, N...

Crop Management Effects on Root and Crown Rot of Wheat in West‐Central Saskatchewan, Canada

The impact of cropping system management on root and crown rot of spring wheat (Triticum aestivum L.) was examined on a Dark Brown Chernozem (Typic Boroll) soil in the Canadian Prairies. This systems approach tried to reflect the most common practices of organic and conventional producers in this region. The study consisted of a factorial combination of three input levels (high, with tillage, fertilizer and pesticides; reduced [RED], with conservation tillage, targeted fertilizer and weed control; and organic [ORG] with tillage and N‐fixing legumes); and three levels of cropping diversity (low diversity with wheat and summerfallow or legume green manure fallow; diversified using annual grain crops; and diversified using annual grain crops and perennial forages). All rotations were 6 yr long. Subcrown internodes and crowns/lower culms of wheat plants were scored for discoloration, and fungi in discolored tissue were identified and quantified. Overall, input level had a greater impact on disease levels and fungal frequency than cropping diversity. Discoloration severity was lowest in the RED systems, which was attributed to lower percentage isolation of Cochliobolus sativus, the most common pathogen. Fusarium species varied with input level. The pathogens F. avenaceum and F. culmorum were most associated with RED and/or least associated with ORG systems, whereas the weak pathogen/saprophyte F. equiseti was most associated with ORG systems. Thus, ORG management helped to reduce populations of F. avenaceum and F. culmorum, two of the most important Fusarium pathogens in the Canadian Prairies.

Sucessão entre cultivos orgânicos de milho e couve consorciados com leguminosas em plantio direto

Práticas agrícolas têm sido desenvolvidas para reduzir a aplicação de insumos químicos e minimizar as agressões ao meio ambiente, produzindo alimentos mais saudáveis e ecologicamente corretos. Portanto, o objetivo deste trabalho foi avaliar o desempenho da sucessão entre couve (Brassica oleracea L. var. acephala) e milho (Zea may L.), em consórcio com leguminosas para fins de adubação verde, sob plantio direto em manejo orgânico. O estudo foi conduzido em Seropédica, Região metropolitana do Rio de Janeiro, em dois anos. Utilizaram-se, como adubos verdes, mucuna-anã (Mucuna deeringiana) e crotalária spectabilis (Crotalaria spectabilis) em consórcio com couve e em sucessão crotalária juncea (Crotalaria juncea) e mucuna-cinza (Mucuna pruriens) em consórcio com milho. Como controles utilizaram-se os monocultivos de couve e milho. O delineamento foi em blocos ao acaso, constituindo fatorial 3 (sistema de cultivo) x 2 (doses de cama-de-frango), com quatro repetições, em parcelas de 20 m². Na couve, aplicou-se em cobertura cama-de-frango nas doses 0 e 5,4 t ha-1 (2,7 t ha-1 em duas aplicações) em 2003 e 0 e 2,7 t ha-1 em 2004. Em monocultivo, a produtividade da couve foi de 37,7 e 18,4 t ha-1; consorciada com mucuna-anã, foi de 40,3 e 38,8 t ha-1 e com crotalária spectabilis, de 42,9 e 24,8 t ha-1, em 2003 e 2004, respectivamente. O milho beneficiou-se do efeito residual da adubação com cama-de-frango, aumentando o número de espigas produzidas de 25.625 para 27.916 ha-1. O cultivo de couve em sucessão ao milho, consorciada com leguminosas anuais, sob adubação orgânica com cama-de-frango, resultou em aumento de produtividade das culturas de couve e milho.

Managing faba bean residues to enhance the fruit quality of the melon ( Cucumis melo L.) crop

Mulching and/or topsoil incorporation of plant residues from green manure legumes can increase cropping system sustainability, and can supply and retain nutrients. Two field experiments were conducted in Italy over the period of 2006–2007, to investigate the effect of faba bean grown in a temperate environment to fruit morphology, quality and chemical composition of the subsequent melon ( Cucumis melo L.) crop. Flowering faba bean plants were managed as mulch on the melon plant rows and cut and incorporated into the soil, in comparison with cultivated soil (control) and black plastic mulch. The plastic mulch increased the soil temperature by about 2 °C compared to cultivated soil. Interestingly, melon plants mulched with faba bean plants and plastic produced higher fruit weight and pulp percentage, but the soil management practices also affected fruit chemical composition. Plastic mulch and faba bean plants induced an increase of total soluble solids and a decrease of acidity. Plastic mulch alone induced the lowest glucose content (0.13 g 100 g −1); treatments with faba bean plants favored the highest fructose accumulation in melon fruits (0.23 g 100 g −1). No clear differences emerged among the treatments with regard to sucrose accumulation in ‘Baggio’, but the faba bean plants managed as mulch induced a high sucrose concentration in ‘Yago’ fruits. Treatments with faba bean plants induced the highest K + accumulation (3324 and 3077 mg kg −1 f.w.); in fact, K + scarcely accumulated in melon fruits harvested from plants mulched with plastic (2543 mg kg −1 f.w.). Faba bean mulching also drastically increased the PO 4 3− accumulation. However, unclear responses were obtained for SO 4 2− increment for ‘Baggio’, while ‘Yago’ showed drastic SO 4 2− accumulation by mulching with faba bean plants. The soil treatments did not affect the accumulation of Mg 2+.

Alternative Strategies for Transitioning to Organic Production in Direct-Seeded Grain Systems in Eastern Washington I: Crop Agronomy

Organic grain production is not common to eastern Washington, but offers attractive market opportunities if systems can be developed that are compatible with regional production constraints. Erodible soils make tillage-intensive systems unsustainable, and there are limited alternative fertility options. Given these constraints, the objective of this study was to evaluate nine cropping systems during the transition to organic grain production under reduced tillage and relying on legumes as the primary source of crop nitrogen. The experimental transition systems ranged in the degree in which legume grain crops or legume green manures/forages were present in the rotation. We found that spring pea grown for grain to be a poor choice for organic production due to the susceptibility of this crop to insect pests and weeds, which generally resulted in crop failure. Likewise, bell bean was poorly suited as a legume green manure crop due to its low productivity in our region. In contrast, alfalfa and winter pea-based systems achieved the best legume biomass production, weed suppression, and crop yields in the subsequent crops. Winter wheat substantially out-yielded spring wheat, but the yields of both of these crops were well below the yield potential typically achieved under conventional production. Competition from annual weeds, such as wild oat and prickly lettuce, and the perennial weed field bindweed was difficult to manage under the reduced tillage regimes employed in this study.

ROTATION IN CONSERVATION AGRICULTURE SYSTEMS OF ZAMBIA: EFFECTS ON SOIL QUALITY AND WATER RELATIONS

SUMMARYConservation agriculture (CA) systems are based on minimal soil disturbance, crop residue retention and crop rotation. Although the capacity of rotations to break pest and disease cycles is generally recognized, other benefits of crop rotations in CA systems are seldom acknowledged and little understood. We monitored different conventional and CA cropping systems over the period from 2005 to 2009 in a multi-seasonal trial in Monze, southern Zambia. Both monocropped maize and different maize rotations including cotton and the green manure cover crop sunnhemp (Crotalaria juncea) were compared under CA conditions, with the aim of elucidating the effects of crop rotations on soil quality, soil moisture relations and maize productivity. Infiltration, a sensitive indicator of soil quality, was significantly lower on conventionally ploughed plots in all cropping seasons compared to CA plots. Higher water infiltration rate led to greater soil moisture content in CA maize treatments seeded after cotton. Earthworm populations, total carbon and aggregate stability were also significantly higher on CA plots. Improvements in soil quality resulted in higher rainfall use efficiency and higher maize grain yield on CA plots especially those in a two- or three-year rotation. In the 2007/08 and 2008/2009 season, highest yields were obtained from direct-seeded maize after sunnhemp, which yielded 74% and 136% more than maize in the conventionally ploughed control treatment with a continuous maize crop. Even in a two-year rotation (maize-cotton), without a legume green manure cover crop, 47% and 38% higher maize yields were recorded compared to maize in the conventionally ploughed control in the two years, respectively. This suggests that there are positive effects from crop rotations even in the absence of disease and pest problems. The overall profitability of each system will, however, depend on markets and prices, which will guide the farmer's decision on which, if any, rotation to choose.

Effect of green manure legume - maize rotation on maize grain yield and weed infestation levels

The use of green manure legumes (GLM) as cover crops in rotation with maize has the potential to enhance maize yields. The objectives of this study were to determine the effect of GML - maize rotation system on (i) maize growth and yield and, (ii) weed infestation levels. The two year (2007/8 and 2008/9 seasons) rotation system consisted of five GML cover crops, viz. mucuna, lablab, sunhemp, cowpea and butterfly pea followed by maize. GML biomass ranged between 0.8 and 13.6 Mg ha-1, while nitrogen (N) content ranged between 10 and 279 kg N ha-1. Maize grain yield following GML ranged between 2.6 and 10.59 Mg ha-1. In 2007/8 season cowpea, mucuna, lablab and sunhemp plots had a lower weed dry matter (5.30, 11.97, 5.83 and 21.03 g m-2, respectively) than the control (+N) (49.47 g m-2). In 2008/9 season, at 6 - 8 WAP, control (+N) had a higher weed dry matter than the other treatments, except of butterfly pea. The dominant weed species were Mexican ricardia (Ricardia brasiliensis), Yellow nutsedge (Cyperus esculentus), Guinea-fowl grass (Rottbollia cochinchinesis), Witch weed (Striga asiatica), Bermuda grass and Cynodon species. Green manure legume fallows can increase maize grain yield significantly and suppress the weed population as compared to natural fallow. However, maximizing biomass production and N accumulation is critical in order to reap the benefits of green manure. Hence, integrating GML into the existing cropping system will require that appropriate timing for planting GML be well established. Key words: Green manure legume, maize, rotation, weed infestation.

Biomass Production and Nitrogen Fixation of Tropical Green Manure Legumes Grown under Pot Condition

Biomass Production and Nitrogen Fixation of Tropical Green Manure Legumes Grown under Pot Condition

Abstracts of Nippon Dojo-Hiryogaku Zasshi

Abstracts of Nippon Dojo-Hiryogaku Zasshi

Decomposition and nitrogen release by green manure legume residues in different soil types

A laboratory incubation experiment was conducted over a 16-week period to determine decomposition and N release by three green manure legume species, Mucuna (Mucuna pruriens), Lablab (Lablab purpureus cv. Rongai) and Sunhemp (Crotalaria juncea), in three soil types from South Africa. The amount of N mineralized from the residues was determined at 2, 4, 8 and 16 weeks from the onset of incubation. Nitrogen release pattern of the three legume residues followed a similar pattern in all the three soils, with sunhemp treated soil having the highest amount of mineral N after 16 weeks of incubation in all the three soils, followed by lablab and then mucuna. The amount of mineral N ranged from 121 to170, 96 to 134 and 92 to 108 mg kg-1 in the sunhemp, lablab and mucuna treated soils, respectively. The cumulative amounts of N from the legume residues mineralized recovered as mineral N in soil after 16 weeks of incubation ranged from 21 - 41% (92 - 121 mg kg-1), 30 - 68% (108 - 170 mg kg-1) and 26 - 60% (93 - 147 mg kg-1) of the initial added N contained in the residues in the soils with 62, 20 and 12% clay contents, respectively. Less than 50% of the initial added N was mineralized in the high clay content soil. Mineralization rate constant, k, was significantly correlated to the residue N content, net mineralized N, C/N ratio and Lignin/N ratio. Results from this study indicated that all the three legumes could contribute significant amounts of N for uptake by plants, with sunhemp tending to release N at a faster rate, followed by lablab and then mucuna. High clay content in soil slowed down N mineralization. Key words: Green manure legumes, incubation, decomposition, N release, soil type.

Moisture conservation and nitrogen recycling through legume mulching in rainfed maize (Zea mays)–wheat (Triticum aestivum) cropping system

Mulching with vegetative materials is a highly beneficial and widely-investigated agro-technique in rainfed areas but the adoption of this practice has been constrained due to non-availability of mulch biomass locally. Live mulching with fast-growing annual green manure legumes like sunnhemp (Crotalaria juncea) or prunings of Leucaena leucocephala grown as hedge rows can be done for moisture conservation as well as nutrient cycling in the maize–wheat cropping system, which is predominantly followed in the high rainfall sub-mountainous region of north-western India. A field experiment was conducted at Selakui, Dehradun during 2000–2004 to study the effect of legume mulching, viz. in situ grown sunnhemp and Leucaena prunings, along with varying N levels, viz. 0, 30, 60 and 90 kg N ha−1 (to maize), and 0, 40 and 80 kg N ha−1 (to wheat) on productivity, soil moisture conservation and soil physico-chemical properties. Intercropped sunnhemp added 0.75–1.45 t dry matter and 21.6–41.3 kg N ha−1 at 30–35 days, while Leucaena twigs added 1.89–4.15 t dry matter and 75.2–161.3 kg N ha−1 at 60–65 days of maize growth. Live mulching with sunnhemp or Leucaena biomass improved soil moisture content at maize harvest (+1.15–1.57%) and crop productivity by 6.8–8.8% over no mulching. Combined use of both the mulching materials was more effective in improving the soil moisture content (+2.08–2.29%) and grain yield (15.1%) over their single application. Response of maize to N fertilizer application was significant up to 90 kg N ha−1, and it was relatively more pronounced under the mulching treatments. Residual effect of mulching on wheat showed an increase in yield of 10.2% with sunnhemp or Leucaena, and 27.9% with sunnhemp + Leucaena. There was an improvement in organic C and total N status of soil, and a decrease in bulk density associated with an increase in infiltration rate due to mulching at the end of 4 cropping cycles. It was concluded that legume mulching is a highly beneficial practice for enhanced moisture and nutrient conservation, leading to increased productivity and soil health of maize–wheat cropping system under Doon valley conditions of north-western India.