Legume-based Cropping Systems Research Articles

Will Phosphate Bio-Solubilization Stimulate Biological Nitrogen Fixation in Grain Legumes?

Biological nitrogen fixation (BNF) refers to a bacterially mediated process by which atmospheric N2is reduced, either symbiotically or non-symbiotically, into ammonia (NH3) in the presence of the enzyme complex nitrogenase. In N2-fixing grain legumes, BNF is often hampered under low phosphorus (P) availability. The P status of legumes, particularly nodules, as well as P availability in the rhizosphere, play a vital role in regulating BNF. Aside from increasing P availability via fertilization, other plant traits (i.e., extensive rooting system and their spatial distribution, hyper-nodulation, root exudates, rhizosphere acidification, and heterogeneity) contribute to greater P uptake and hence more effective BNF. The positive interaction between P availability and BNF can be exploited through beneficial soil P solubilizing microorganisms (PSM). These microorganisms can increase plant-available P by modifying either rhizosphere soil processes or promoting plant traits, which lead to increased P uptake by the production of plant growth-promoting substances, both of which could indirectly influence the efficiency of BNF in legumes. In this review, we report on the importance of microbial P bio-solubilization as a pathway for improving BNF in grain legumes via PSM and P solubilizing bacteria (PSB). Because BNF in legumes is a P-requiring agro-ecological process, the ability of soil PSB to synergize with the rhizobial strains is likely a key belowground process worth investigating for advanced research aiming to improve rhizosphere biological functions necessary for sustainable legume-based cropping systems.

Integrated crop management technology for enhanced productivity, resource-use efficiency and soil health in legumes – A review

Under impeding production–and resource–vulnerabilities in India, our approach to agriculture needs to be redefined with inclination towards climate resilient integrated crop and resource management (ICRM) having low risk vulnerability, high factor productivity and sustained farm profitability with safe food and environmental quality. In above context, integrated crop management (ICM) practices hold great potential which take into account economic, social and environment sustainability. In irrigated agro-ecosystem of Indo-Gangetic Plains Region (IGPR), continuous cultivation of rice-wheat cropping system (RWCS) with intensive input use has caused a serious threat to agricultural sustainability with numerous production constraints. In order to diversify the IGPR production systems, pulses and other legumes like soybean and pigeonpea etc. hold great promises. Thus, legume-based cropping systems coupled with ICM practices may bring overall sustainability in IGPR. As per FAO, ICM is a recent concept in agriculture. ICM practices are the integrated technology package of appropriate site-specific crop management, integrated nutrient management, crop residue recycling, tillage management, water management, crop diversification/legume intervention, varietal selection, crop protection, energy saving and post-harvest management. Overall, this review paper highlights sufficient research findings which establish the superiority of ICM practices; in addition, it invokes for further strengthening of this research area for improving agricultural productivity, resource use efficiency and soil health with special reference to legume crops.

Combining on-farm innovation tracking and participatory prototyping trials to develop legume-based cropping systems in West Africa

In the cotton-production zone of Burkina Faso, poor soil fertility and limited access to appropriate fertilizers call for alternative approaches to sustain productivity, such as the introduction of more legumes into the agroecosystem. Legumes have nearly disappeared from local cropping systems under the pressure of the cotton monocropping model. To develop new legume-based cropping systems using a bottom-up approach, this study was based on local farmers' agroecological innovations. In a first step, called on-farm innovation tracking, five innovative legume-based cropping systems were identified and characterized on farms located in the study area through interviews with “innovative farmers” who had designed and implemented these cropping systems: (i) Sorghum and legume (cowpea, soybean or peanut) intercropping in rotation with maize or cotton; (ii) Soybean as a cash crop in rotation with maize or cotton; (iii) Red cowpea intra-annual succession with a biomass crop; (iv) Mucuna in rotation with maize; and (v) Pigeon pea in rotation with maize. In a second step, these five “innovative cropping systems” (ICSs) were implemented in “participatory prototyping trials” (PPTs) in two communities located in the study area were they were evaluated during field days by local farmers (“field-day farmers”) having no previous experience with ICSs. By comparing evaluations made by innovative farmers with those of field-day farmers, it was shown that (i) locally implemented ICSs adapted to local drivers of change are of great interest to other farmers, and (ii) the study's two-step participatory approach is an original and relevant way to co-design and introduce innovations.

Soil nutrient loss through erosion: Impact of different cropping systems and soil amendments in Ghana.

Soil erosion is a multifactor threat to crop production and the environment. Most studies on soil erosion characterization have not focused on soil nutrient loss associated with erosion. The aim of this study was therefore to quantify the magnitude of nutrient loss through soil erosion under different cropping systems and amendments to inform agronomic practices in sub-Saharan Africa (SSA). A field experiment was carried out on runoff plots with different cropping systems (sole maize, sole cowpea, sole maize and maize intercropped with soybean) as main plots and soil amendments (biochar, NPK (Nitrogen +Phosphorus +Potassium) fertilizer, NPK + biochar and a control (no amendment)) constituting the subplots in a randomized complete block design. For each block, a bare plot was included to assess the efficiency of the different crop and soil management practices on soil erosion. The study was carried out in three consecutive cropping seasons in the semi-deciduous forest zone of Ghana. The bare plots had the highest amounts of nitrogen (N), phosphorus (P), and potassium (K) eroded: 33.88, 12.35 and 12.75 kg ha-1 respectively followed by the control plots with magnitude of 20.43, 8.42 and 7.87 kg ha-1 respectively for N, P and K. Sole maize had the highest amounts of nutrient loss: 19.71, 8.12 and 7.27 for N, P and K respectively compared to all the other cropping systems where the losses varied respectively from 12.38 to 17.12, 6.67 to 7.49 and 5.81 to 6.75 kg ha-1 The legume-based cropping systems under inorganic fertilizer and biochar management effectively reduced nutrient loss more than all other treatment combinations. The off-site effect of soil erosion expressed as enrichment ratio (ER) was higher for all plots, which received inorganic fertilizer inputs varying from 1.93 to 3.06 while the other treatments had ERs of 1.51 to 2.03. The ERs of fine soil particles were greater than 1 (ranging from 1.14 to 3.6) being relatively higher than that of coarse particles (sand) with values below 1 (ranging from 0.62 to 0.88). The least cumulative monetary value of nutrient loss (30.82 US$ ha-1) was observed under cowpea cropping system which received NPK + BC treatment. Soil erosion affected directly soil nutrient depletion through nutrient loss; however, integrated soil fertility management associated with legume-based cropping systems can be alternative options to reducing its effects on croplands in SSA.

Design, assessment and feasibility of legume-based cropping systems in three European regions

Grain legumes in cropping systems result in agronomic and environmental benefits. Nevertheless, their areas in Europe have strongly decreased over the past decades. Our aim was to design locally adapted innovative cropping systems including grain legumes for three European local pedoclimatic contexts, to assess their sustainability, and to discuss their feasibility with stakeholders. The methodology included an initial diagnosis of the most frequent cropping systems and local improvement targets in each local context (e.g. improve legume profitability, limit diseases of legumes, reduce intensive use of chemical inputs in cropping systems), the design of innovative legume-based cropping systems during a common workshop, focusing on three aims ((i) decrease pesticide use, (ii) reduce mineral N fertiliser dependency, and (iii) increase yield stability of grain legume crops and other crops of the crop sequence), and their multicriteria sustainability assessment. Stakeholders meetings were organised in each local context to discuss the feasibility of implementing the innovative cropping systems in farmers’ fields (technical implementation of cropping systems and possibility of development of legume sectors). Four to five cropping systems were designed in each local context, with crop sequences longer than references. They included at least two grain legumes (pea, faba bean, chickpea, lentil or lupine), as sole crops or intercropped with cereals. Overall sustainability was similar or improved in 71% of the legume-based cropping systems compared with their corresponding references. Among the designed cropping systems, stakeholders identified feasible ones considering both technical issues and development of legume sectors. The results indicate that reintegrating more grain legumes in the three European local contexts tested will contribute to more sustainable farming systems.

Cover crops mitigate nitrate leaching in cropping systems including grain legumes: Field evidence and model simulations

Grain legume-based cropping systems need to be designed holistically by taking profit of their advantages (e.g. symbiotic fixation of N2) while reducing environmental risks. In this experiment we studied the impact of the incorporation of cover crops in grain legume-based rotations on the mitigation of nitrate leaching and recycling of N for the subsequent cash crop. A cropping system experiment (2004–2010) with three 3-year rotations of different number of grain legumes (GL0, GL1 and GL2, none, one and two grain legumes, respectively) with (CC) or without (BF, bare fallow) cover crops was established at INRA Auzeville (SW France). Soil water and mineral N contents of the entire profile (0–120cm depth) were measured three times per season at key stages. Shoot cash and cover crop biomass and biomass N concentration were measured and the N acquisition of the different crops was calculated. In addition, the STICS soil–crop dynamic model was used to simulate the amount of daily water drained and N leached under the different rotations studied. STICS performed reasonably well when simulating soil water and soil nitrate contents, crop biomass and N acquired, allowing water drainage and nitrate leaching fluxes to be modelled with confidence. Globally, simulated N leaching was low due to amount of rainfall received during the experimental period which was lower than the 30-year average. As an average of the different crop sequences the cumulative N leaching during the experimental period (i.e. 2004–2010) increased when increasing the number of grain legumes in the rotation when no cover crops were used. However, the use of cover crops reduced N leaching. Within each rotation, cash crop N uptake did not differ between the BF and CC treatments. Our study highlights the importance of a proper design of entire cropping systems, i.e. simultaneously cash crop succession and cover crop, by adapting the crop rotation and the different management practices (i.e. N fertilization, irrigation, etc.) to mitigate the environmental impact of N leaching and reduce as much as possible pre-emptive competition phenomena due to cover crops.

Soil nitrous oxide emissions as affected by long-term tillage, cropping systems and nitrogen fertilization in Southern Brazil

Soil nitrous oxide (N2O) emissions are affected by management practices, but little information is available on the interactive effects of tillage, cropping systems and N sources in tropical and subtropical soils. In an 18-yr old experiment located in a subtropical Acrisol of Southern Brazil we conducted a sequence of two trials. The 1-year trial (October 2003–2004) was set to evaluate the long-term effects of tillage [CT: conventional; and NT: no-tillage] and cropping systems [O/M: black oat (Avena strigosa Schreb.)/maize (Zea mays L.); and V/M: vetch (Vicia sativa L.)/maize] on soil N2O emissions, either in the post-management period (45 days after desiccation and knife-rolling of winter cover crops) or in the whole year. The second and short-term trial (October–November 2004) was carried out to compare the impact of N sources [urea (mineral) and legume-residue of vetch (biologically fixed), both at 180kgNha−1] on soil N2O emissions during 53 days after cover-crop management. Air sampling was carried out by static chambers and N2O analysis by gas chromatography. In the 45-day post-management period of the 1-year trial, soil N2O emissions were practically not affected by tillage systems, but increased 4 times due to vetch residues (average of 0.40±0.08kgNha−1 in V/M versus 0.10±0.05kgNha−1 in O/M) and related with soil contents of NO3−-N, NH4+-N, and dissolved organic C (DOC). Over the whole year, soil N2O emissions under CT were similar for grass- and legume-based cropping systems and averaged 0.43±0.17kgNha−1, while NT exacerbated N2O emissions in the legume-based cropping system (0.80±0.07kgNha−1 in V/M versus −0.07±0.06kgNha−1 in O/M). Maize yield was not affected by tillage, but increased from 2.32Mgha−1 in O/M to 4.44Mgha−1 in V/M. Yield-scaled N2O emissions varied from −33g N2O-NMg−1 grain in NT O/M to 179g N2O-NMg−1 grain in NT V/M, and were intermediate in CT soil (106 and 156g N2O-NMg−1grain in V/M and O/M cropping systems, respectively). In the short-term trial, the N2O emitted in excess relative to the control treatment (O/M without N fertilizer) was at least 3 times greater with urea-N (0.44% of applied N) than with legume-residue-Nsource (0.13% of applied N). Yield-scaled N2O emission after vetch residues management (67gNMg−1 grain) was half of that after urea-N application (152gNMg−1 grain). Partially supplying the maize N requirements with winter legume cover-crops may be a feasible strategy to mitigate soil N2O emissions in the subtropical conservation agriculture.

Nitrous oxide and methane emissions from a vetch cropping season are changed by long-term tillage practices in a Mediterranean agroecosystem

Lower greenhouse gas (GHG) emissions from legume-based cropping systems have encouraged their use to deliver mitigation in agricultural systems. Considerable uncertainties remain about the interaction of legumes with long-term tillage systems on GHG emissions under rainfed agroecosystems. In this context, a field experiment was undertaken under a rainfed vetch crop to evaluate the effect of three long-term tillage systems (i.e. no tillage (NT), minimum tillage (MT) and conventional tillage (CT)) on nitrous oxide (N2O) and methane (CH4) emissions for 1 year. Different N2O flux patterns were observed among tillage systems during the growth period of vetch, which depended on the soil conditions favouring nitrification and denitrification. The NT system maintained a higher sink for N2O than MT and CT from January to mid-April, which significantly reduced N2O emissions at this stage. In this period, denitrification capacity and nirK gene numbers were higher for MT than NT and CT. Additionally, an increase in soil NO3− content and more favourable denitrification conditions in MT and NT than in CT for the last crop period increased N2O emissions in conservation tillage systems. Total annual N2O losses were significantly higher in MT (124.2 g N2O–N ha−1) than NT (51.1 g N2O–N ha−1) and CT (54 g N2O–N ha−1) in a vetch crop. Low net uptake of CH4 was observed for all tillage systems. These results suggested that long-term NT may be a better option than MT to mitigate GHG emissions in rainfed legume-cereal rotation.

Do You Think it is Time to Consider Legume-Based Cropping Systems Again?

Do You Think it is Time to Consider Legume-Based Cropping Systems Again?

Nitrogen use and food production in European regions from a global perspective

SUMMARYCurrent production systems for crops, meat, dairy and bioenergy in the European Union (EU) rely strongly on the external input of nitrogen (N). These systems show a high productivity per unit of land. However, the drawback is a complex web of N pollution problems contributing in a major way to degradation of ecosystems. European Union Directives and national policies have improved nutrient management and reduced fertilizer N use in most European countries, which has curbed the N pollution trends particularly in regions with high stocking rates of animals. However, improvement is slowing down and environmental targets for N are not within reach. Building on the 2011 European Nitrogen Assessment, the current paper reviews key features of the complex relationships between N use and food production in Europe in order to develop novel options for a more N-efficient, less N-polluting and secure European food system. One option is to relocate feed and livestock production from Northwestern to Central and Eastern Europe. This would allow a reduction of N rates and N pollution in cereal production in Northwest Europe by 30% (50 kg N/ha), while increasing total cereal production in Europe. Another option is a change towards legume-based cropping systems to produce animal feed, in order to decrease dependence on N fertilizer and feed imports. The greatest challenge for Europe is to decrease the demand for feed commodities, and thus for land and N, by a shift to more balanced (and healthier) diets with less animal protein. These drastic changes can be stimulated by targeted public–private research funding, while the actual implementation can be enhanced by smart payment schemes using, for example money from the Common Agricultural Policy, certification and agreements between stakeholders and players in the food and energy chain. Involving networks of consumers, producers and non-governmental organizations is critical. An effective strategy starts with convincing consumers with a Western diet to eat less meat and dairy by communicating the associated health benefits and smaller ecological footprints. Internalizing the cost of N pollution leading to increased prices for N-intensive food products may also enhance involvement of consumers and provide financial resources to compensate farmers for loss of income and extra costs for stricter N measures.

Yield Comparison of Nonstructural Carbohydrates in Sweet Sorghum and Legume-Based Cropping Systems

Field experiments were conducted during dry (2009/10) and wet (2010) seasons to evaluate sweet sorghum–legume-based cropping systems for soluble sugars and starch production. Treatments were composed of two types of legumes (mung bean, soybean), two planting patterns (alternate single rows, alternate double rows), and two times of seeding (simultaneous, staggered) together with three monocrop treatments of sweet sorghum, mung bean, and soybean in randomized complete block design. Key observations indicated that the average yields of soluble sugars and starch were significantly reduced in intercropping systems in both seasons, due to partial or interactive influence of treatments considered. Yields of soluble sugars and starch were increased by 6 and 11% in the dry season and by 5 and 19% in the wet season in sweet sorghum–soybean and sweet sorghum–mung bean associations, respectively, when established with staggered seeding compared to those in simultaneously seeded combination or in monocropping of sweet sorghum.

Roles of soil biological interations in enhancing food security

In developed countries, continuous monocropping, high-disturbance tillage, and ready access to synthetic inputs have allowed farmers and researchers to obtain high crop yields with little regard for soil biology. An unrecognized “opportunity cost” associated with large-scale agriculture is the depletion of soil biological complexity, which may taken many years to restore. The opportunity costs of biologically depleted soils, however, have not been incurred in much of the developing world because synthetic inputs have been much less accessible to the small landholder. Indeed, the developing world can ill afford to overlook the potential benefits of plant-microbe and microbe-microbe interactions which occur in soils when available nutrients are low. How then can farmers and researchers best take advantage of indigenous soil biological interactions which can enhance nutrient availability in agricultural systems? This overview describes ways by which soil biology can be “harnessed” more efficiently in agriculture through use of soil-specific inoculants, legume-based cropping systems, and incorporation of locally derived materials that would not otherwise be directed to livestock.Keywords: soil microorganisms, plant nutrients, rhizobacteria, mycorrhizae, soil disturbance, plant-microbe interactionsNigerian Journal of Technological Research

Carbon fractions and productivity under changed climate scenario in soybean–wheat system

Global climate change is anticipated to have a tremendous influence on crop productivity and nutrient cycling in legume-based cropping systems. The effect of long-term application of manure and fertilizers on the dynamics of soil organic carbon (SOC) pools and soil physical properties was studied in a soybean (Glycine max Merr. L)–wheat (Triticum aestivum L.) system. The temperature sensitivity of C pools and the alterations in microbial composition were determined at 25, 35, and 45°C. Higher levels of microbial biomass C (MBC) and nitrogen (MBN), water soluble carbon (WSC), acid hydrolysable carbohydrates (AHC), particulate organic matter carbon (POMC) and nitrogen (POMN) were observed in the NPK+FYM at a depth of 0–15cm. Irrespective of the treatment, micro aggregates (53–250μm) were a major aggregate size class, comprising 45–57% of the total soil aggregates, followed by macro aggregates (250–2000μm at 37.8–45%). Microbial respiration rate increased by 13.9% in most recalcitrant pools (<53μm) at 45°C than at 25°C. Furthermore, data on labile C (A0) revealed a 4.9–55.4% increase in the substrate pools and a 10.5–32.5% increase in mineralization rate (k) with these treatments at 25–45°C in 250–2000μm aggregates. AHC and POMC content decreased by 23–37% and 12–23% of SOC, respectively, when the temperature was raised from 25 to 45°C. It is concluded the gradual depletion of nutrients, structural degradation and changes in microbial composition might have collectively contributed to the decline in crop yields. It was suggested that temperature has a strong effect on C mineralization, depending on the types and extents of substrate utilization. Seasonal rainfall, maximum and minimum temperature and SOC had jointly explained 12–41% of variation in soybean production in NP, NPK and NPK+FYM treatments. However, balanced use of NPK plus FYM is an important management option to arrest the decline of crop yield.

Soil dehydrogenase activity in agro-ecological sub regions of black soil regions in India

A survey was undertaken in the established benchmark (BM) soil series in different agro-ecological sub regions (AESR) of Black Soil Regions (BSR) in India with an objective to study the impacts of bio-climates, cropping systems and land use systems on the distribution of dehydrogenase activity (DHA) in different soil profiles. The DHA was found to decline with depth and the maximum activity was recorded within 0–30cm soil depth. Cropping systems and bio-climates significantly (p<0.01) influence the DHA in soil. Significantly (p<0.01) higher DHA was recorded in Sub-humid moist (SHm) bio-climate (2.45μg TPFg−1) followed by Semi-arid dry (SAd) (2.00μg TPFg−1) and the least in arid bio-climate (1.62μg TPFg−1). The average DHA in different bio-climates were in decreasing order of Sub-humid moist>Semi-arid dry>Sub-humid dry>arid. Legume-based cropping system recorded higher DHA (2.32–2.88μg TPFg−1) followed by cereal-based cropping system (1.29–2.82μg TPFg−1). The average DHA in different cropping systems were in decreasing order of legume>cereals>cotton>sugarcane. The comparisons of DHA in different soils indicated significant differences (p<0.01) between the soil sub groups. High management practices found to significantly increase DHA (2.15μg TPFg−1) compared to low management (1.78μg TPFg−1), whilst no significant differences were found in DHA between irrigated and rainfed system.

Combined role of no-tillage and cropping systems in soil carbon stocks and stabilization

Increases in carbon (C) input and stabilization are key processes to turn soils into sinks of atmospheric CO2–C and help mitigating global warming. We hypothesized (i) that C sequestration in no-tillage soil is further enhanced by high input cropping systems and (ii) that the sequestered C is stored mainly in the mineral associated fraction. The objective of this study was to assess, in 2003, the C sequestration and stabilization in a subtropical Acrisol (Eldorado do Sul, Brazil) subjected to 18-year conventional tillage [CT] and no-tillage [NT] combined with two cropping systems: black oat (Avena strigosa Schreb) as winter cover crop – maize (Zea mays L.) as summer grain crop [Ot/M]; and black oat plus vetch (Vicia villosa Roth) as winter cover crops – maize in summer intercropped with cowpea (Vigna unguiculata (L.) Walp) cover crop [Ot+V/M+C]. Soil C stock in the 0–20cm layer was higher in NT than in CT, either in Ot/M (31.1 vs. 27.8Mgha−1, P<0.05) or Ot+V/M+C (37.3 vs. 32.8Mgha−1, P<0.05). Annual C sequestration rate in NT relative to CT was 0.25Mgha−1 in Ot+V/M+C and 0.18Mgha−1 in Ot/M, in agreement to the higher biomass-C addition and legume cover crops inclusion in Ot+V/M+C (7.6 vs 4.0Mgha−1 year−1) and to our first hypothesis. Increase in the proportion of large macroaggregates (9.51–4.76mm) and of mean weight diameter occurred in NT soil up to 10cm depth, both in Ot/M and Ot+V/M+C. In NT, most of the C accumulation relative to CT occurred in the mineral-associated fraction, showing the importance of organo-mineral interaction in C stabilization and supporting our second hypothesis. However, the physical protection by aggregates played equally important role by stabilizing the occluded particulate organic matter (occluded-POM) before it was further stabilized by organo-mineral interaction. No-tillage is recommended as a sustainable soil management, but to increase soil C accumulation, the potential of cropping systems such those based on legume cover crops must be concurrently explored.

Methane emission from soil under long-term no-till cropping systems

Methane (CH4) emission from agricultural soils increases dramatically as a result of deleterious effect of soil disturbance and nitrogen fertilization on methanotrophic organisms; however, few studies have attempted to evaluate the potential of long-term conservation management systems to mitigate CH4 emissions in tropical and subtropical soils. This study aimed to evaluate the long-term effect (>19 years) of no-till grass- and legume-based cropping systems on annual soil CH4 fluxes in a formerly degraded Acrisol in Southern Brazil. Air sampling was carried out using static chambers and CH4 analysis by gas chromatography. Analysis of historical data set of the experiment evidenced a remarkable effect of high C- and N-input cropping systems on the improvement of biological, chemical, and physical characteristics of this no-tilled soil. Soil CH4 fluxes, which represent a net balance between consumption (−) and production (+) of CH4 in soil, varied from −40±2 to +62±78μg Cm−2h−1. Mean weighted contents of ammonium (NH4+–N) and dissolved organic carbon (DOC) in soil had a positive relationship with accumulated soil CH4 fluxes in the post-management period (r2=0.95, p=0.05), suggesting an additive effect of these nutrients in suppressing CH4 oxidation and stimulating methanogenesis, respectively, in legume-based cropping systems with high biomass input. Annual CH4 fluxes ranged from −50±610 to +994±105g Cha−1, which were inversely related to annual biomass-C input (r2=0.99, p=0.003), with the exception of the cropping system containing pigeon pea, a summer legume that had the highest biologically fixed N input (>300kgha−1yr−1). Our results evidenced a small effect of conservation management systems on decreasing CH4 emissions from soil, despite their significant effect restoring soil quality. We hypothesized that soil CH4 uptake strength has been off-set by an injurious effect of biologically fixed N in legume-based cropping systems on soil methanotrophic microbiota, and by the methanogenesis increase as a result of the O2 depletion in niches of high biological activity in the surface layer of the no-tillage soil.

Assessing soil nitrogen availability in contrasting cropping systems at the end of transition to organic production

Liu, K., Hammermeister, A. M., Warman, P. R., Drury, C. F. and Martin, R. C. 2011. Assessing soil nitrogen availability in contrasting cropping systems at the end of transition to organic production. Can. J. Soil Sci. 91: 493–501. Quantifying soil nitrogen (N) availability at the end of a transition period for converting conventional fields to organic fields could enhance N management during the subsequent organic crop production phase. Soil total N (Ntot), KCl extractable N (KCl N) and potentially mineralizable N (No) were determined at the end of a 3-yr transition period. A complementary greenhouse ryegrass N bioassay was conducted using soils collected from the treated field plots. The field experiment consisted of six cropping systems comprising two N inputs (legume-based vs. manure-based) and three forage cropping treatments (0, 1 or 2 yr of forage in 4-yr rotations). The N input treatments consisted of alfalfa meal in the legume-based cropping system (LBCS) and composted beef manure in the manure-based cropping system (MBCS). Orthogonal contrasts suggested no differences in Ntot or KCl N either between LBCS and MBCS or between no-forage and forage cropping systems. However, in the greenhouse study, high cumulative N inputs in the MBCS resulted in significantly higher ryegrass N uptake and potentially mineralizable soil N than in the LBCS. Ryegrass N uptake ranged from 101 to 139 kg ha−1, which should be an adequate N supply for the succeeding potato crop. In the greenhouse, a ryegrass N bioassay effectively identified the differences in soil N availability. Ryegrass N uptake was linearly related to cumulative soil amendment N inputs but had no apparent relationship with N o. A systems approach provided a good assessment of N availability at the end of the transition period to organic production.

Grain legume impacts on soil biological processes in sub-Saharan Africa

Grain legumes occupy about 20 million hectares in Africa. The major crops are cowpea (Vigna unguiculata L.), which is grown on about 11 million hectares mostly in West Africa, and common bean (Phaseolus vulgaris L.), grown on about 5 million hectares mostly in eastern and southern Africa. These grain legumes have impacted soil organisms, including nitrogen fixers, mycorrhizae, fauna, and the processes that they perform. The legume-Rhizobium symbiosis results in dinitrogen (N2) fixation that adds plant-available nitrogen to the soil system. Some of the fixed N2 is recycled when legume crop residues decompose for the benefit of non-legume crops grown with or after grain legumes. This N recycled by grain legumes is minimal because most of the N in these legumes is in the grain that is removed from the farm at harvest. Non-legume crops grown in rotation with legumes may also benefit from endophytic rhizobia. Mycorrhizal associations that improve plant nutrient and water uptake also benefit from the legume in a cropping system. Besides breaking pest cycles, grain legume crops also reduce disease infestation of non-legume crops by enhancing biological pest control through increased microbial diversity and activity. Legumes may contribute to greenhouse gas (nitrous oxide and carbon dioxide) emissions during nitrification and denitrification of fixed N2. However, because less fertilizer N is used in legume-based cropping systems, overall greenhouse gas emissions are usually less than those in fertilized monoculture cereals. Through their effects on soil biology, legume crops also improve soil structure by enhancing the formation and maintenance of soil aggregates. Therefore, grain legumes in Sub-Saharan Africa have positive effects on agriculture by adding and recycling biologically fixed N2, enhancing nutrient uptake, reducing greenhouse gas emissions, and improving soil structure and breaking non-legume crop pest cycles.

Estoque e disponibilidade de nitrogênio no solo em experimento de longa duração

O N é o nutriente requerido em maior quantidade pelas culturas agrícolas em geral e, normalmente, é o maior limitante de seu rendimento. Neste estudo, objetivou-se avaliar o efeito de sistemas de culturas no estoque de N total do solo e na disponibilidade deste nutriente. O estudo foi desenvolvido em um experimento de longa duração (22 anos), em um Argissolo Vermelho distrófico típico localizado na Estação Experimental Agronômica da Universidade Federal do Rio Grande do Sul (30 ° 50 ' 52 '' sul e 51 ° 38 ' 08 '' oeste), em Eldorado do Sul, RS. Este experimento iniciou-se em 1983 e está sendo realizado desde sua implantação sob sistema plantio direto, com dez sistemas de culturas (solo descoberto, pousio/milho, aveia/milho, pangola, aveia + ervilhaca/milho com solo corrigido e revolvido até 70 cm em 1992, aveia + ervilhaca/milho, aveia + ervilhaca/milho + caupi, guandu + lablabe, lablabe + milho e guandu + milho) e duas doses de N (0 e 180 kg ha-1) aplicadas no milho. Foram avaliados os estoques de N total do solo na camada de 0-20 cm em 2005 e estimadas as quantidades de N fixadas pelas leguminosas e perdidas do adubo nitrogenado mineral em 22 anos. Adicionalmente, foi avaliado o N acumulado pela aveia cultivada em sucessão ao milho em 2006. O estoque de N total, que era de 3.040 kg ha-1 em 1983, variou em 2005 de 2.500 a 4.800 kg ha-1, sendo os maiores estoques encontrados nos sistemas com leguminosas e adubação nitrogenada. A quantidade estimada de N fixado pelas leguminosas variou de 800 a 1.980 kg ha-1 e, na média, 48 % do N mineral aplicado no milho (3.180 kg ha-1) foi perdido do sistema solo-planta. Os maiores estoques de N total refletiram-se nas maiores quantidades de N acumulado pela aveia que variaram de 17 a 100 kg ha-1.

Carbon management index based on physical fractionation of soil organic matter in an Acrisol under long-term no-till cropping systems

The carbon management index (CMI) is derived from the total soil organic C pool and C lability and is useful to evaluate the capacity of management systems to promote soil quality. However, the CMI has not been commonly used for this purpose, possible due to some limitations of the 333 mM KMnO 4-chemical oxidation method conventionally employed to determine the labile C fraction. We hypothesized, however, that physical fractionation of organic matter is an alternative approach to determine the labile C. The objectives of this study were (i) to assess the physical fractionation with density (NaI 1.8 Mg m −3) and particle-size separation (53 μm mesh) as alternative methods to the KMnO 4-chemical oxidation (60 and 333 mM) in determining the labile C and thus the CMI, and (ii) to evaluate the capacity of long-term (19 years) no-till cropping systems (oat/maize: O/M, oat + vetch/maize: O + V/M, oat + vetch/maize + cowpea: O + V/M + C, and pigeon pea + maize: P + M) and N fertilization (0 and 180 kg N ha −1) to promote the soil quality of a Southern Brazilian Acrisol, using the CMI as the main assessment parameter. Soil samples were collected from 0 to 12.5 cm layer, and the soil of an adjacent native grassland was taken as reference. The mean annual C input of the cropping systems varied from 3.4 to 6.0 Mg ha −1 and the highest amounts occurred in legume-based cropping systems and N fertilized treatments. The C pool index was positively related to the annual C input ( r 2 = 0.93, P < 0.002). The labile C determined by density (4.4–10.4% of C pool) and particle-size separation (9.5–17.7% of C pool) had a close relationship ( r = 0.60 and 0.85, respectively) with the labile C determined using 60 mM KMnO 4 (7.3–10.5% of C pool). The labile C resulting from the three methods was related to the annual C input imparted by the cropping systems ( r 2 = 0.67–0.88), reinforcing the possibility of using physical fractionation as an alternative approach to determine labile C. In contrast, the chemical method using 333 mM KMnO 4 was not sensitive to different cropping systems and resulted in too high percentage of labile C, varying from 16.8 to 35.2% of the C pool. The CMI based on physical fractionation was a sensitive tool for assessing the capacity of management systems to promote soil quality, as evidenced by its close correlation ( r = 0.88, at average) with soil physical, chemical, and biological attributes. The introduction of winter (vetch) and, especially, summer legume cover crops (cowpea and pigeon pea), or application of fertilizer-N, improved the capacity of the management system into promote soil quality in this subtropical Acrisol.