Winter legumes as a nitrogen source for no-tillage cotton

Winter legumes can serve dual purposes in no-tillage cropping systems. They can provide a no-tillage mulch, and supply a considerable quantity of N for thesummer crops. Cotton (Gossypium hirsutum L.) was no-tillage planted into crimson clover (Trifolium incarnatum L.), common vetch (Vicia sativa L.), and fallowed soil for two years to determine the effects of winter legume mulches on growth, yield, and N fertilizer requirements. The legumes were allowed to mature and reseed prior to planting cotton. The winter legumes produced no measurable changes in soil organic matter, N, or bulk density, but water infiltration was more rapid in the legume plots than in the fallowed soil. In the fallow system, 34 kg ha^?1 N fertilizer was required for near maximum yields. In the clover plots, yields without N fertilizer were higher than when N (34 and 68 kg ha^?1) was applied. In the vetch plots, cotton yields were highest without N fertilizer the first year, but yields were increased with 34 kg ha^?1 N the second year because of a poor vetch seed crop and a subsequently poor legume stand. In the clover plots, a 20–30% cotton seedling mortality occurred in one year, but this stand reduction apparently did not affect cotton yields. Winter legume mulches can provide the N needs for no-tillage cotton without causing an excessive and detrimental quantity of N in sandy soils naturally low in soil N (0.04%). Unless the reseeding legume systems are maintained for at least 3 years, the legumes do not, however, provide an economical N source for cotton when N fertilizer requirementsare low (34 kg ha^?1 in this study). A possible disadvantage of the system for reseeding legumes is that cotton planting is delayed 4–6 weeks beyond the normal planting date, which can reduce yields in some years.     

Winter legume and tillage effects on cotton growth and soil ecology

Field studies were conducted at 2 locations in Alabama during 1984 and 1985 to identify cultural practices which would improve cotton (Gossypium hirsutum L.) stands when plantned no-till into winter legumes. The soils were a Decatur silt loam (Rhodic Paleudult) and a Norfolk sandy loam (Typic Paleudult). The experimental design was a randomized complete block with 4 replications. Whole plots consisted of winter annual legumes (Vicia villosa Roth or Trifolium incarnatum L.) and fallow areas. Split-plot treatments established at cotton planting included conventional and conservation tillage, and fungicide. Soil samples were collected at cotton planting for population determination of Collembola and Acari species, and for estimation of cotton-disease fungus (Rhizoctonia solani) infestation. Collembola populations were greater in the Decatur than Norfolk soils, and higher in legume-mulched than fallow soils by 39 and 72% for the Decatur and Norfolk soil, respectively. Disease infestation in the Decatur soil was 10% higher in legume than fallow plots, and 18% higher in legume than fallow plots in the Norfolk soil. Cotton populations were 19% less in legume than fallow areas, and 25% less with conservation (no-till) than with standard tillage. Bedding improved cotton stands by 21% compared to conservation tillage. Seed-cotton yields from the Decatur soil were consistently high (3798 kg ha⁻¹, and there was no yield response to treatments. Maximum seed-cotton yields at the Norfolk site were achieved with conservation tillage in the fallow area, and conventional tillage in the legume area (both receiving fungicide).     

Effect of phosphorus management in rice–mungbean rotations on sandy soils of Cambodia

Nitrogen (N) and phosphorus (P) deficiencies are key constraints in rainfed lowland rice (Oryza sativa L.) production systems of Cambodia. Only small amounts of mineral N and P or of organic amendment are annually applied to a single crop of rainfed lowland rice by smallholder farmers. The integration of leguminous crops in the pre‐rice cropping niche can contribute to diversify the production, supply of C and N, and contribute to soil fertility improvement for the subsequent crop of rice. However, the performance of leguminous crops is restricted even more than that of rice by low available soil P. An alternative strategy involves the application of mineral P that is destined to the rice crop already to the legume. This P supply is likely to stimulate legume growth and biological N₂ fixation, thus enhancing C and N inputs and recycling N and P upon legume residue incorporation. Rotation experiments were conducted in farmers' fields in 2013–2014 to assess the effects of P management on biomass accumulation and N₂ fixation (δ¹⁵N) by mungbean (Vigna radiata L.) and possible carry‐over effects on rice in two contrasting representative soils (highly infertile and moderately fertile sandy Fluvisol). In the traditional system (no legume), unamended lowland rice (no N, + 10 kg P ha^?1) yielded 2.8 and 4.0 t ha^?1, which increased to 3.5 and 4.7 t ha^?1 with the application of 25 kg ha^?1 of urea‐N in the infertile and the moderately fertile soil, respectively. The integration of mungbean as a green manure contributed up to 9 kg of biologically fixed N (17% Nfda), increasing rice yields only moderately to 3.5–4.6 t ha^?1. However, applying P to mungbean stimulated legume growth and enhanced the BNF contribution up to 21 kg N ha^?1 (36% Nfda). Rice yields resulting from legume residue incorporation (“green manure use”–all residues returned and “grain legume use”–only stover returned) increased to 4.2 and 4.9 t ha^?1 in the infertile and moderately fertile soil, respectively. The “forage legume use” (all above‐ground residues removed) provided no yield effect. In general, legume residue incorporation was more beneficial in the infertile than in the moderately fertile soil. We conclude that the inclusion of mungbean into the prevailing low‐input rainfed production systems of Cambodia can increase rice yield, provided that small amounts of P are applied to the legume. Differences in the attributes of the two major soil types in the region require a site‐specific targeting of the suggested legume and P management strategies, with largest benefits likely to accrue on infertile soils.     

Impact of a 5-year winter cover crop rotational system on the molecular diversity of arbuscular mycorrhizal fungi colonizing roots of subsequent soybean

The impact of winter cover crops, specifically wheat (Triticum aestivum L.), red clover (Trifolium pratense L.), and rapeseed (Brassica napus L.) or winter fallow, on community composition of arbuscular mycorrhizal fungi (AMF) in subsequent soybean roots was investigated in a 5-year field trial on andosolic soils in Japan. Soybean roots were sampled at full-flowering and analyzed for AMF communities using a partial LSU rDNA region. Phylogenetic analysis detected 22 AMF phylotypes, including eight Glomus, three Gigaspora, two Scutellospora, three Acaulospora, two Rhizophagus, and one of Funneliformis, Diversispora, Paraglomus, and an unknown glomeromycete in the roots. The 5-year rotation of different winter cover crops or winter fallow did not impact the molecular diversity of AMF communities colonizing the roots of subsequent soybean. In all of the rotations, Glomus and Gigaspora phylotypes were common to soybean roots over the 5-year period. Redundancy analysis (RDA) demonstrated that AMF communities in the roots of subsequent soybean were not significantly different among winter cover crop rotations or fallow. However, AMF communities in soybean roots were clearly influenced by rotation year suggesting that climate or other environmental factors were more important than winter cover cropping system management.     

Increased pepper yields following incorporation of biofumigation cover crops and the effects on soilborne pathogen populations and pepper diseases

The use of brassica cover crops and their associated degradation compounds as biofumigants to manage soilborne pathogens could offer vegetable growers an alternative to the restricted broad-spectrum fumigant methyl bromide. Biofumigation was tested in two experiments to manage Rhizoctonia solani, Sclerotium rolfsii, and Pythium spp., and the diseases they cause on pepper. Field plots were seeded in fall 2010 and spring 2011 to oilseed radish (Raphanus sativus L.), ‘Pacific Gold’ mustard (Brassica juncea (L.) Czern), or ‘Dwarf Essex’ winter rapeseed (Brassica napus L.). Cover crops were disked into soil in spring 2011 and immediately covered with virtually impermeable film (VIF) to reduce the escape of volatile pesticidal compounds. Controls included fallow plots with (CVIF) and without (fallow) VIF. Green bell pepper was transplanted into all plots. Concentrations of isothiocyanates (ITCs), the brassica degradation compounds primarily responsible for pesticidal activity, were highest following incorporation of mustard. Rapeseed yielded the second highest ITC concentrations. Radish yielded very low ITC concentrations in experiment 1, and none during experiment 2. ITCs also were detected in low concentrations in CVIF treatments. All treatments that received VIF reduced populations of R. solani compared to fallow, with no differences between biofumigation treatments and CVIF. Biofumigation treatments did not reduce populations of Pythium spp. or S. rolfsii compared to CVIF. Pepper stunting was significantly lower in treatments that received VIF compared to fallow, with no consistently significant differences between biofumigation treatments and CVIF. Pythium isolated from roots of stunted peppers was identified as Pythium aphanidermatum. Biofumigation treatments did not reduce plant mortality. Pepper yields were highest in biofumigation treatments compared to CVIF, and CVIF yields were higher than fallow yields.     

Fallow residue management effects on upland rice in three agroecological zones of West Africa

Improving fallow quality in upland rice-fallow rotations in West Africa through the site-specific use of leguminous cover crops has been shown to sustain the productivity of such systems. We studied the effects of a range of residue management practices (removal, burning, mulching and incorporation) on fallow biomass and N accumulation, on weed biomass and yield response of upland rice and on changes in soil physical and chemical characteristics in 2-year field trials conducted in three agroecological zones of Côte d'Ivoire. Across fallow management treatments and agroecological zones, rice yields were on average 20–30% higher in legume than in natural fallow plots. Weed biomass was highest in the savanna zone and lowest in the bimodal forest and tended to be less following a legume fallow. Regardless of the type of fallow vegetation and agroecological zone, biomass removal resulted in the lowest rice yields that varied from 0.5?t ha^–1 in the derived savanna zone to 1.5?t ha^–1 in the Guinea savanna zone. Burning of the fallow vegetation significantly increased yield over residue removal in the derived savanna (0.27?t ha^–1, P<0.05) and bimodal forest zones (0.27?t ha^–1, P<0.01), but not in the Guinea savanna. In both savanna environments, residue incorporation was superior to the farmers' practice of residue removal and rice yield increases were related to amounts of fallow N returned to the soil (r²=0.803, P<0.01). In the forest zone, the farmers' practice of residue burning produced the highest yield (1.43?t ha-1 in the case of legumes) and resulted in the lowest weed biomass (0.02?t ha^–1). Regardless of the site, improving the quality of the fallow or of its management had no significant effects on either soil physical or soil chemical characteristics after two fallow cycles. We conclude that incorporation of legume residues is a desirable practice for rice-based fallow rotation systems in savanna environments. No promising residue management alternatives to slash-and-burn were apparent for the forest zone. Determining the possible effects on soil productivity will require longer-term experiments.     

WINTER CROPS AS BIOASSAYS OF SOIL NITROGEN-SUPPLYING CAPACITY

Soil nitrogen (N)-supplying capacity bioassays could present alternatives to traditional soil tests. Objectives were to identify winter crops and associated characteristics with bioassay potential. Saint Joseph and Bossier City, LA experiments used randomized complete block designs with factorial N fertilizer and winter crop treatment arrangements. Nitrogen rates were applied to corn (Zea mays L.) in 2004. Unfertilized winter wheat ( Triticum aestivum L.), cereal rye (Secale cereale L.), native winter vegetation, and weed-free winter fallow treatments followed corn. At Saint Joseph, cotton (Gossypium hirsutum L.) followed winter crop treatments. Greater corn N rate consistently increased winter crop biomass and N accumulation, suggesting potential as bioassays, and increased Saint Joseph seedcotton yield. Winter crop-seedcotton yield N-response relationships were non-significant by familywise error rate criteria. However, some winter crop characteristics, such as rye N accumulation, for which a relationship to seedcotton yield closely approached significance, may merit further research as soil N-supplying capacity bioassays.     

不同绿肥和覆膜措施对渭北旱塬冬小麦产量和土壤水分动态的影响

  【目的】  冬小麦—绿肥轮作在干旱贫水年份易导致冬小麦减产,我们研究了平水年和干旱年旱地绿肥和覆膜措施相结合对小麦产量及水分利用率的影响,为建立科学高效的小麦–绿肥轮作体系奠定基础。  【方法】  田间试验于2017—2019年布设在陕西省永寿县御驾宫乡御中村,试验采用裂区试验设计,以轮作不同绿肥品种(黑麦豆、油菜,夏休闲为对照)为主处理,覆膜措施为副处理,设常规耕作和垄覆沟播两个水平。在冬小麦返青期、开花期、收获期调查小麦苗期生长状况、产量形成、水分利用效率和麦田0—200 cm土壤水分动态变化。  【结果】  1)平水年和干旱年,轮作油菜的冬小麦产量高于轮作黑麦豆,两年间轮作油菜处理比轮作黑麦豆处理的冬小麦产量分别高出 9.3%和43.5% (P<0.05)。2)采用垄覆沟播,轮作绿肥显著降低了冬小麦生育期耗水量,平水年提高了冬小麦的水分利用效率。平水年轮作油菜的水分利用效率最高[14.3 kg/(hm2·mm)],比夏休闲处理增加了7.4%;而干旱年轮作绿肥降低了冬小麦的水分利用效率,与夏休闲相比轮作黑麦豆和油菜处理分别降低58.5%和38.3% (P<0.05)。轮作绿肥与垄覆沟播对提高小麦水分利用效率有显著的交互作用。3)轮作绿肥并垄覆沟播的栽培模式加重了土壤水分的消耗。相比于夏休闲,平水年冬小麦播前0—200 cm土壤贮水量平均降低10.1% (P<0.05),干旱年平均降低15.7% (P<0.05)。  【结论】  我国渭北旱塬地区在平水年采用种植油菜+垄覆沟播新型种植模式,可以在保证不减产的情况下提高冬小麦的水分利用效率,但干旱年小麦产量和水分利用效率均会受到负面影响。     

Effects of various cover crops after peas on nitrate leaching and nitrogen supply to succeeding winter wheat or potato crops

In organic farming systems, it has been demonstrated that grain pulses such as peas often do not enhance soil N supply to the following crops. This may be due to large N removals via harvested grains as well as N‐leaching losses during winter. In two field‐trial series, the effects of legume (common vetch, hairy vetch, peas) and nonlegume (oil radish) cover crops (CC), and mixtures of both, sown after peas, on soil nitrate content, N uptake, and yield of following potatoes or winter wheat were studied. The overall objective of these experiments was to obtain detailed information on how to influence N availability after main‐crop peas by adapting cover‐cropping strategies. Cover crops accumulated 56 to 108 kg N ha^–1 in aboveground biomass, and legume CC fixed 30–70 kg N ha^–1 by N₂ fixation, depending on the soil N supply and the length of the growing period of the CC. Nitrogen concentration in the aboveground biomass of legume CC was much higher and the C : N ratio much lower than in the nonlegume oil radish CC. At the time of CC incorporation (wheat series) as well as at the end of the growing season (potato series), soil nitrate content did not differ between the nonlegume CC species and mixtures, whereas pure stands of legume CC showed slightly increased soil nitrate content. When the CC were incorporated in autumn (beginning of October) nitrate leaching increased, especially from leguminous CC. However, most of the N leached only into soil layers down to 1.50 m and was recovered more or less by the following winter wheat. When CC were incorporated in late winter (February) no increase in nitrate leaching was observed. In spring, N availability for winter wheat or potatoes was much greater after legumes and, after mixtures containing legumes, resulting in significantly higher N uptake and yields in both crops. In conclusion, autumn‐incorporated CC mixtures of legumes and nonlegumes accomplished both: reduced nitrate leaching and larger N availability to the succeeding crop. When the CC were incorporated in winter and a spring‐sown main crop followed even pure stands of legume CC were able to achieve both goals.     

Response of Different Crops to Arbuscular Mycorrhiza Fungal Inoculation in Phosphorus-Deficient Soil

Arbuscular mycorrhizal fungi (AMF) have the capability to improve crop yields by increasing plant nutrient supply. A pot experiment was conducted under natural conditions to determine the response of AMF inoculation on the growth of maize (Zea mays L.), sorghum (Sorghum bicolor L.), millet (Pennisetum glaucum L.), mash bean (Vigna mungo L.), and mung bean (Vigna radiata. L.) crops during 2008. The experiment was conducted as a completely randomized design in three replications using phosphorus (P)–deficient soil. Three plants were grown in 10 kg soil up to the stage of maximum growth for 70 days. Spores of AMF were isolated from rhizosphere of freshly growing wheat and berseem crops and mixed with sterilized soil with fine particles. Crops were inoculated in the presence of indigenous mycorrhiza with the inoculum containing 20 g sterilized soil mixed with 40–50 AMF spores. Inoculation with AMF improved yield and nutrient uptake by different crops significantly over uninoculated crops. Inoculated millet crop showed 20% increase in shoot dry matter and 21% in root dry matter when compared with other inoculated crops. Increases of 67% in plant nitrogen (N) and iron (Fe) were observed in millet, 166% in plant P uptake was observed in mash beans, 186% in zinc (Zn) was measured in maize, and 208% in copper (Cu) and 48% in manganese (Mn) were noted in sorghum crops. Maximum root infection intensity of 35% by AMF and their soil spore density were observed in millet crop followed by 32% in mash beans. Results suggest that inoculation of AMF may play a role in improving crop production and the varied response of different crops to fungi signifies the importance of evaluating the compatibility of the fungi and plant host species.     

Legumes as dry season fallow in upland rice-based systems of West Africa

Declining fallow length in traditional upland rice-based cropping systems in West Africa results in a significant yield reduction due mainly to increased weed pressure and declining soil fertility. Promising cropping system alternatives include the use of weed-suppressing legumes as short duration fallows. N accumulation, N derived from the atmosphere (Ndfa), weed suppression, and the effects on rice yield were evaluated in 50 legumes, grown at four sites in Côte d'Ivoire with contrasting climate, soils, and rice production systems. The sites were located in the derived and the Guinea savanna and in the bimodal and the monomodal rainfall forest zones. Legume and weed biomass during the fallow were determined at bimonthly intervals. Percent Ndfa by biological N fixation was determined by ¹⁵N natural abundance. Fallow vegetation was cleared and rice seeded according to the practice of local farmers and the cropping calendar. Weed biomass and species composition were monitored at monthly intervals. Legume fallows appear to offer the potential to sustain rice yields under intensified cropping. Biomass was in most instances significantly greater in the legume fallow than in the "weedy" fallow control, and several legume species suppressed weed growth. N accumulation by legumes varied between 1–270?kg N ha^–1 with 30–90%?Ndfa. Across sites, Mucuna spp., Canavalia spp., and Stylosanthes guianensis showed consistently high N accumulation. Grain yields of rice which had been preceded by a legume fallow were on average 0.2?Mg ha^–1 or about 30% greater than that preceded by a natural weedy fallow control. At the savanna sites where fallow vegetation was incorporated, Mucuna spp. and Canavalia ensiformis significantly increased rice yield. In the bimodal forest zone, the highest rice yield and lowest weed biomass were obtained with Crotalaria anagyroides. In general, the effects of legume fallows on rice yield were most significant in environments with favourable soil and hydrological conditions.     

Incorporation of catch crop residues does not increase phosphorus leaching: a soil column experiment in unsaturated conditions

Some studies suggest that incorporation of catch crop residues leads to increased availability of P to plants. However, little information is available on how this affects P leaching in soils with a high P load. We tested the effect of catch‐crop residue incorporation at the end of winter on the P leaching potential in a soil column experiment under unsaturated conditions using a typical sandy loam soil of NW Europe characterized by a high P load. We sampled the catch crops white mustard (Sinapis alba L.), Italian ryegrass (Lolium multiflorum L.), black oats (Avena strigosa L.) and a perennial ryegrass‐white clover mix (Lolium perenne L.‐Trifolium repens L.) from a field trial on catch crops and soil from the plots where they were grown. Plant biomass was incorporated taking account of the differences in conditions of the plant material at the end of winter and the biomass yield of each catch crop. Incorporation of catch‐crop residues decreased P leaching compared to the fallow treatment probably through immobilization of soil P during catch crop residue decomposition. The exception was black oats, where the leaching of P was the same as for fallow soil. We observed clear differences in C/N, C/P, water soluble and total P concentration, and biodegradability between the tested catch crops, which seemed to affect the P leaching. We conclude that the incorporation of catch crop residues under typical soil and weather conditions and agricultural practices of NW Europe does not increase the potential P leaching losses.     

The effect of starter fertilizers on cotton production in legume residues

Abstract

Field and greenhouse studies were conducted to identify starter fertilizers which would enhance cotton seedling survival, growth, and yield in legume residues. Field studies were initiated in the fall of 1982 on a Norfolk sandy loam (Typic Paleudult) in the Upper Coastal Plain of Alabama. Winter annual legumes, crimson clover (Trifolium incarnatum L.) and hairy vetch (Vicia villosa Roth) were established as whole plots along with a winter fallow area. Split plot treatments consisted of O, N, P, K, NP, NK, and NPK starter fertilizers. The cotton (Gossypium hirsutum L.) was planted with a conservation tillage planting unit with in‐row subsoilers. The starter fertilizers were applied deep (8 to 10 inches) in the subsoil track. Greenhouse studies were also conducted with soil from whole plot areas top dressed with corresponding legume tissue at a rate of .9 g tissue/500 g soil. Seedlings in the greenhouse were rated for disease and emergence, and dry weights were recorded.

Cotton populations in field studies were lower in legume mulched than fallow soils in 1984. Application of starter fertilizers generally increased harvest populations, particularly the NK combination. In 1983, cotton growth was greater in vetch than other soils, but responses to starter fertilizers varied with analyses and years. Seed cotton yields were consistently high with P starter, although P did not always improve cotton stands and growth. When averaged across years and cover crops, yields were 3151, 3031, 2865, 2790, 2753, 2741, 2512, and 2364 for P, NP, P, NP, K, NPK, N and O, starter treatments respectively.

Greenhouse studies indicated that starter fertilizer improved cotton emergence in legume soils, but decreased emergence in fallow soils. Disease ratings of emerged seedlings were more severe when starter fertilizer was used than when it was not used. Thus, starter fertilizer increased emergence and survival, despite high disease ratings. Cotton seedling growth generally increased when poor emergence reduced cotton seedling competition.     

苏南稻田4种冬绿肥养分特性及对翻压前土壤无机氮的影响

为充分利用苏南冬闲稻田发展适宜绿肥作物种植,在大田试验条件下,研究了毛叶苕子（Vicia villosa Roth）、 光叶苕子（Vicia villosa var.）、 紫云英（Astragalus sinicus L.）和肥田萝卜（Raphanus sativus L.）4种绿肥作物的生长、 营养特性,比较分析了绿肥作物翻压前不同处理间耕层土壤无机氮含量与构成的差异。结果表明,在绿肥作物翻压期,4种绿肥作物均达到较高生物量和养分累积量,鲜重、 干重分别为24.8 30.7 t/hm2和3.6 4.2 t/hm2,不同绿肥作物间无显著差异。 4种绿肥作物的吸氮量为69.8 136.4 kg/hm2,毛叶苕子最高,肥田萝卜最低。吸磷量为7.1~11.3 kg/hm2,肥田萝卜最高,紫云英最低。吸钾量为117.6~151.3 kg/hm2,毛叶苕子最高,光叶苕子最低。与对照冬闲相比,种植绿肥作物不同程度地降低了耕层土壤无机氮含量（平均降低38.9 kg/hm2）,其中硝态氮含量下降明显,铵态氮含量均较对照土壤有增加趋势（平均提高6.5 kg/hm2）,毛叶苕子和光叶苕子处理铵态氮含量增加显著。4种绿肥作物均适合苏南冬闲稻田种植,能潜在降低无机氮的损失风险和为后季水稻作物生长提供养分。     

Influence of ammonia fertilization on cotton production in conservation tillage systems

Abstract

Field studies were conducted to determine the influence of ammonia fertilization on cotton grown in conservation tillage systems. The studies were located on a Decatur silt loam (Rhodic Paleudult) in the Limestone Valley and a Norfolk sandy loam (Typic Paleudult) in the Coastal Plain of Alabama. Winter annual legumes, crimson clover (Trifolium incarnatum L. at the Norfolk site) and hairy vetch (Vicia villosa Roth at the Decatur site) were established as whole plots along with a winter fallow area. Sources of fertilizer differing widely in their NH₄+‐N contents were used for split plot treatments applied at time of cotton (Gossypium hirsutum L.) planting. Fertilizer treatments included calcium nitrate, ammonium nitrate, urea, urea with dicyandiamide, and a no N check. The cotton was planted with a strip‐till conservation planter. Nitrogen production by winter legumes was adequate to meet N requirements for cotton on the Decatur silt loam (67 kg N/ha) but not at the Norfolk sandy loam site (101 kg N/ha). Cotton populations were 24% higher in fallow than legume whole plots. Differences in plant growth and N concentrations were highly variable and treatment trends were not found. Seed cotton yields were 4% higher in fallow than legume plots. Maximum populations and yields were achieved with ammonium nitrate in fallow area and urea in legume areas.     

Soil carbon as affected by cover crops under no‐till under tropical climate

In tropical, low‐fertility soils, crop yields are dependent on soil carbon, and cropping systems under no‐till can increase soil C stocks. Plant residues supplied by cover crops in no‐till systems may improve aggregate stability and soil carbon, which may be further increased with the introduction of a legume in the cropping system. This research studied the effects of cover crops in rotation with soybean under no‐till on soil carbon and nitrogen, in Botucatu, Brazil, for 3 yr. The cover crops were millet (Penninsetum americanum Leek), cober crop (Sorghum bicolor × Sorghum sudanense) and sunn hemp (Crotalaria juncea L.), grown in the spring. Fallow without cover crops was used as a control. Grain sorghum (Sorghum bicolor L. Moench) and soybean (Glycine max (L.) Merril) were grown in fall–winter and summer, respectively. Generally, cover crops increased soil carbon contents, but soil N was only increased by sunn hemp in the particulate organic C fraction. An increase in the labile carbon fraction in the topsoil layers was closely related to cover crop root development. Fallow in spring should not be recommended in degraded soils with lowcarbon stock. Labile‐fractioned soil organic carbon and total carbon levels are more efficiently increased by grasses than by legumes in the short term, and grasses cropped in spring increase soil C/N ratio. Conversely, the introduction of a legume (sunn hemp) maintained a more stable C/N ratio, that is around 10, which would be more effective in increasing soil C in the long term.     

Nitrogen uptake in organically managed spring sown lupins and residual effects on leaching and yield of a following winter cereal

Three unfertilized spring sown species of lupins (Lupinus angustifolius) and peas (Pisum sativa) were compared in terms of N fixation and subsequent leaching under a following winter barley crop in an organically managed rotation. Fallow plots were included to assess the potential weed burden and the ability of the sown crops to compete with weeds when no herbicides were applied. Although peas out-yielded lupins (5.4 t compared with 3.5 t grain respectively), the yellow lupin (Wodjil) fixed more N than peas (180 compared with 120 kg N/ha) and all three lupins had higher protein contents (>30%) than peas (22%). Winter leaching amounted to >50 kg nitrate-N/ha from winter barley, regardless of whether it followed treatments which were previously fallow or cropped with legumes. There were no significant differences in leaching between the lupin species. Leachate in the first 350 mm of drainage under winter barley, following the different legume species, exceeded the European Union limit for nitrate in drinking water in all treatments. Yields of winter barley, grown without fertilizers or herbicides following legumes, were not significantly different (mean 4 t/ha), but there were higher levels of P and K in the grain compared with the amounts made available from the previously fallow soil. At this site in SW England, the crops grew well and our results suggest that lupins could provide a useful break crop in an organic arable cropping rotation and an alternative source of home-grown, high protein feed.     

Upland rice,common bean,and cowpea response to magnesium application on an oxisol

Abstract

Even though Mg is an essential nutrient. the response of upland rice, common bean, and cowpea to Mg application has not been adequately documented in Brazilian oxisols. This study was conducted to examine the influence of Mg application on growth and nutrient uptake by upland rice (Oryza sativa L.), common bean (Phaseolus vulgaris L.), and cowpea (Vigna unguiculata L. Walp.) on an oxisol. Magnesium levels in the soil were created at sowing by application of MgO at rates of 0.30, 1.05, 1.15, 1.33, 3.52, and 6.22 cmol Mg/kg of soil. Application of Mg did not have a significant beneficial effect on dry weight of roots and tops of rice and cowpea. Common bean root and top dry weights were increased with Mg applications up to 1 cmol Mg/kg of soil. Uptake of N, P, K, Ca, Cu, Zn, Fe, and Mn by the three crops was significantly (P < 0.01) decreased by increasing Mg levels in the soil. Results related to changes in chemical properties of soil with the application of Mg are also presented.     

Effect of nutrient management and straw mulching on crop yield,uptake and soil fertility in rapeseed (Brassica campestris)–greengram (Vigna radiata)–rice (Oryza sativa) cropping system under Gangetic plains of India

An experiment was conducted at Bidhan Chandra Krishi Viswavidyalaya, West Bengal, India during 2001–2003 to study the effect of levels of fertility and straw mulch on a rapeseed (Brassica campestris var yellow sarson)–greengram (Vigna radiata)–rice (Oryza sativa) cropping system under a rainfed upland ecosystem. The experiment was laid out in a split-plot design having 14 treatment combinations of organic and inorganic nutrients along with straw mulch in three replicates. The results revealed that conjunctive use of organic and inorganic nutrients as well as paddy straw mulch resulted higher yield in both rapeseed and greengram, and the residual effects of different levels of fertilization and mulching also gave rise to higher grain yield in the succeeding rice crop. The uptake of nutrients, by the cropping system as a whole, to the tune of 204.29 and 183.00 kg ha^?1 of N, 72.84 and 74.07 kg ha^?1 of P and 179.95 and 175.41 kg ha^?1 of K took place, with the treatment receiving 10 t ha^?1 of farmyard manure (FYM) applied (to rapeseed) along with 50% recommended dose (RD) of NPK to all the crops in the sequence in two consecutive years, respectively. The same treatment resulted in a higher percentage of porosity vis-à-vis lower bulk density. Soil physico-chemical properties were superior in mulch-treated plots compared with no mulch treatment. Application of organic and inorganic nutrients along with proper moisture conservation practices can enhance the yields maintaining a good soil health.     

Changes of Soil Microbial Biomass Carbon and Nitrogen with Cover Crops and Irrigation in a Tomato Field

ABSTRACT

In order to understand how soil microbial biomass was influenced by incorporated residues of summer cover crops and by water regimes, soil microbial biomass carbon (C) and nitrogen (N) were investigated in tomato field plots in which three leguminous and a non-leguminous cover crop had been grown and incorporated into the soil. The cover crops were sunn hemp (Crotalaria juncea L., cv ‘Tropic Sun’), cowpea (Vigna unguiculata L. Walp, cv ‘Iron clay’), velvetbean (Mucuna deeringiana (Bort) Merr.), and sorghum sudangrass (Sorghum bicolor × S. bicolor var. sudanense (Piper) Stapf) vs. a fallow (bare soil). The tomato crop was irrigated at four different rates, i.e., irrigation initiated only when the water tension had reached ?5, ?10, ?20, or ?30 kPa, respectively. The results showed that sorghum sudangrass, cowpea, sunn hemp, and velvetbean increased microbial biomass C by 68.9%, 89.8%, 116.8%, and 137.7%, and microbial N by 58.3%, 100.0%, 297.3%, and 261.3%, respectively. A legume cover crop, cowpea, had no statistically significant greater effect on soil microbial C and N than the non-legume cover crop, sorghum sudangrass. The tropical legumes, velvetbean and sunn hemp, increased the microbial biomass N markedly. However, the various irrigation rates did not cause significant changes in either microbial N or microbial C. Soil microbial biomass was strongly related to the N concentration and/or the inverse of the C:N ratio of the cover crops and in the soil. Tomato plant biomass and tomato fruit yields correlated well with the level of soil microbial N and inversely with the soil C:N ratio. These results suggest that cover crops increase soil microbiological biomass through the decomposition of organic C. Legumes are more effective than non-legumes, because they contain larger quantities of N and lower C:N ratios than non-legumes.