The legacy of stockless organic conversion strategies

Legume‐containing leys are commonly used to improve soil fertility in the 2‐year conversion period from conventional to organic production. While in‐conversion land may be grazed, in stockless farming systems, land is effectively out of production, leading to a reduction in income and pressure on cash flow. The impacts of seven organic conversion strategies on the first organic crop (winter wheat) were previously reported. This study investigates the effect of the conversion strategies on the second (winter beans) and third (winter oats) organic crops, thereby extending the analysis throughout the first complete rotation. The strategies were (a) 2‐years’ red clover–ryegrass green manure, (b) 2‐years’ hairy vetch green manure, (c) red clover for seed production then a red clover–ryegrass green manure, (d) spring wheat undersown with red clover, then a red clover green manure, (e) spring oats, then winter beans, (f) spring wheat, then winter beans and (g) spring wheat undersown with red clover, then a barley–pea intercrop. Conversion strategy had a significant impact on organic bean yield, which ranged from 2.78 to 3.62 t ha^?1, and organic oat yield, which ranged from 3.24 to 4.17 t ha^?1. In the organic bean crop, weed abundance prior to harvest, along with soil texture, accounted for 70% of yield variation. For the oats, soil mineral nitrogen in November together with weed abundance in April accounted for 72% of the variation in yield. The impacts of conversion strategies on soil mineral nitrogen levels were still detectable 3 years after conversion. The results from this study indicate that the choice of conversion crop has important long‐term implications. More exploitative conversion strategies, that is those with a higher proportion of cash cropping, had an increased weed burden and decreased levels of soil mineral nitrogen, leading to reduced yields of beans and oats, 2 and 3 years after conversion.     

Barley response to nitrogen and non-nutritional benefits of legume green manure

Green manure application may benefit subsequent crops not only by improving nitrogen (N) fertility but also via non-nutritional mechanisms. The quantification of the latter effect, however, is complicated by the confounding effect of N fertility. Two experiments were conducted in controlled environments to partition the yield response of barley to green manure between N and non-nutritional effects. Each experiment included a factorial of fertilizer N application rates and green manure application rates. The fertilizer was labelled with ¹⁵N to facilitate discrimination between N sources. Approximately 24% of the N applied in green manure was assimilated by barley after 45 days (Experiment 1) and 32% was recovered by barley grown to maturity (Experiment 2). Apparent recovery of green manure-N by barley was not appreciably affected by fertilizer application. Regression analysis of the relationship between dry matter yield and plant N uptake demonstrated that yield responses to green manure application were not entirely attributable to improved N fertility. For a given amount of N assimilated by the crop, yields were higher in green manure-amended treatments than in those receiving no green manure. In barley grown to maturity, barley response to N and non-nutritional effects were estimated to be 5.3 and 2.2g pot⁻¹, respectively. The relationship between dry matter yield and N uptake is suggested as a method for distinguishing nutritional and non-nutritional yield responses. This approach assumes that no other nutrient is limiting growth. The presence of non-nutritional benefits observed in this study demonstrates that the agronomic value of green manure is not limited to N release and casts doubt on the assumptions inherent to calculation of fertilizer equivalents. Contribution 3879132 Contribution 3879132     

水旱轮作下长期免耕和施用有机肥对土壤某些肥力性状的影响

１９８３年６月至１９９７年１０月进行的水旱轮作下连续免耕并配合施用有肥料的长期定位田间试验研究结果表明,长期免耕和施肥造成土壤养分的表层富集,０－５ｃｍ土层有机磷、全氮、速效氮含量显著增加,而５－１０ｃｍ和１０－２０ｃｍ土层上述养分含量明显低于常规耕翻处理;免耕对土壤结构破坏少,使０－２０ｃｍ土层水稳性团粒结构增多,综合各项肥力性状,不同施肥处理对提高土壤肥力的贡献为：猪粪〉秸秆〉绿肥〉化肥〉不施     

Interactions between white clover and ryegrass under contrasting nitrogen availability: N2 fixation,N fertilizer recovery,N transfer and water use efficiency

Seasonal variation in N₂ fixation, N transfer from clover to ryegrass, and soil N absorption in white clover–ryegrass swards were investigated under field conditions over three consecutive years. The plots were established with different seeding ratios of clover and ryegrass and contrasting fertilizer N ranging from 3 to 72 kg ha^-1 year^-1.An initially poor clover population needed at least one growing season to reach the same yield output as an initially well established clover population. The clover content of the sward decreased by the annual application of 72 kg N ha^-1 but not by smaller N dressings.The total amount of atmospherically derived N in clover growing in mixture with ryegrass was, on average over the three years equal to 83, 71, 68 and 60 kg N ha^-1 for the treatments of 3, 24, 48 and 72 kg N ha^-1, respectively. The proportion of atmospherically derived N declined with increasing N application, but never became smaller than 80% of total clover N. The proportion of atmospherically derived N in a pure stand white clover amounted to 60–80% of the total N content, equivalent to 109, 110, 103 and 90 kg N ha^-1 for the treatments of 3, 24, 48 and 72 kg N ha^-1, respectively.Only small amounts of atmospherically derived N was transferred to the associated ryegrass during the first production year, while in each of the following years up to 21 kg ha^-1 was transferred. The average amount of N transferred from clover to ryegrass was equivalent to 3, 16 and 31% of the N accumulated in ryegrass in the first, second and third production year, respectively. Expressed relative to the total amount of fixed N₂ in the clover–ryegrass mixture, the transfer amounted to 3, 17 and 22% in the first, second and third production year, respectively. Thus transfer of atmospherically derived N from clover contributed significantly to the N economy of the associated ryegrass.The clover–ryegrass mixture absorbed constantly higher amount of soil derived N than the pure stands of the two species. Only 11% of the total accumulated fertilizer N and soil derived N in the mixture was contained within the clover component. Lower water use efficiencies for the plants grown in mixture compared to pure stands were mainly related to the increased N uptake in the mixture, with the subsequent increase in growth compared to the pure stands.It is concluded that positive interactions between clover and ryegrass growing in mixture ensure a more efficient fixation of atmospheric N₂ and absorption of fertilizer N and soil derived N than pure stands of the same species.     

Management of Lesion Nematodes and Potato Early Dying with Rotation Crops

Soil-incorporated rotation/green manure crops were evaluated for management of potato early dying caused by Verticillium dahliae and Pratylenchus penetrans. After two years of rotation/green manure and a subsequent potato crop, P. penetrans numbers were less after ‘Saia’ oat/‘Polynema’ marigold, ‘Triple S’ sorghum-sudangrass, or ‘Garry’ oat than ‘Superior’ potato or ‘Humus’ rapeseed. The area under the disease progress curve (AUDPC) for early dying was lowest after Saia oat/marigold, and tuber yields were greater than continuous potato after all crops except sorghum-sudangrass. Saia oat/marigold crops resulted in the greatest tuber yields. After one year of rotation/green manure, a marigold crop increased tuber yields and reduced AUDPC and P. penetrans. In the second potato crop after a single year of rotation, plots previously planted to marigolds had reduced P. penetrans densities and AUDPC and increased tuber yield. Rapeseed supported more P. penetrans than potato, but had greater yields. After two years of rotation/green manure crops and a subsequent potato crop, continuous potato had the highest AUDPC and lowest tuber weight. Rotation with Saia oats (2 yr) and Rudbeckia hirta (1 yr) reduced P. penetrans and increased tuber yields. AUDPC was lowest after R. hirta. Two years of sorghum-sudangrass did not affect P. penetrans, tuber yield or AUDPC. These results demonstrate that P. penetrans may be reduced by one or two years of rotation to non-host or antagonistic plants such as Saia oat, Polynema marigold, or R. hirta and that nematode control may reduce the severity of potato early dying.     

Development of a low input system for growing wheat (Triticum vulgare) in a permanent understorey of white clover (Trifolium repens)

In three field experiments carried out during 1989-91, a permanent sward of pure white clover (Trifolium repens) was established to provide a source of N for winter or spring wheat crops (Triticum vulgare) directly drilled into the legume. Spring-sown wheat failed to compete with the clover, but wheat sown in the autumn established successfully. N fertiliser was applied to all three experiments at rates of 0, 50 and 100 kg N ha“¹ measurements of grain and whole-crop silage yields were made. Yields were low for all treatments, probably because of the dry conditions prevailing and the low soil N status of the site used. Yield responses to fertiliser were significant, despite the contribution to plant nutrition that the clover was intended to make. A key feature of the work was that the clover survived successive cereal crops and could be grazed and used as an understorey for later crops. Further, response to fertiliser N diminished with a successive crop implying a build-up of available soil N, which measurements confirmed had occurred. Use of the system obviated the need to use pesticides, although reasons for the lack of pest damage were not clear.     

Variation in 15N enrichment of crimson clover labeled under field conditions

Plant material labeled with ¹⁵N is often used to determine recovery of N from green manure crops by subsequent crops. In this study, ¹⁵N enriched crimson clover (Trifolium incarnatum L.) was grown at a field site where it was to be utilized in a subsequent experiment. A foliar spray of (NH₄)₂SO₄ (99 atom % excess ¹⁵N) was applied to a 1.2 m × 8.8 m plot of crimson clover at a rate of 10 kg N ha^–1 in early March 1990, immediately prior to the period of rapid vegetative growth. Clover shoots harvested in April contained 1.72 atom % excess ¹⁵N. Total N concentration of enriched clover was similar to that in adjacent untreated clover. Clover shoots contained 20% of the applied ¹⁵N, and an additional 27% was recovered from the surface soil horizon (0 to 15 cm). A gradient was observed across the plot, with clover enrichment increasing from 1.3 to 2.2 atom % excess ¹⁵N. Recovery of applied ¹⁵N in soil was highest in the subplots with lowest clover enrichment. Variability in ¹⁵N enrichment was also observed among plant parts: leaves from the basal half of shoots had 2.2 atom % excess ¹⁵N; while leaves from the terminal half of shoots, terminal stems, and basal stems had between 1.1 and 1.4 atom % excess ¹⁵N.Abbreviation %Ndf source the percentage of the N atoms in a sample derived from a labeled source     

豆科绿肥及施氮量对旱地麦田土壤主要肥力性状的影响

通过2a田间定位试验,研究渭北旱塬地区夏闲期插播并翻压不同豆科绿肥(长武怀豆、大豆和绿豆)以及小麦生长季不同施氮量(0,108,135,162 kg/hm2)对麦田土壤肥力性状的影响,以期为提高旱地土壤质量提供理论依据.试验结果表明:(1)种植豆科绿肥能显著提高土壤有机质、活性有机质和全氮含量,增加土壤碳库管理指数(CPMI),对土壤速效钾含量没有显著影响;(2)绿豆还田量高于长武怀豆和大豆,然而土壤培肥效果逊于长武怀豆和大豆;(3)夏闲期种植绿肥明显消耗了土壤水分,导致绿肥翻压前、小麦播前直至收获后,0-200 cm土壤贮水量显著低于休闲处理,但耗水量与休闲没有明显差异,由于小麦产量显著增加,因此豆科绿肥显著提高了水分生产效率;(4)与不施氮相比,小麦生长季施用氮肥能显著增加土壤水分生产效率,却对土壤各肥力性状的影响均不显著.夏闲期种植并翻压豆科绿肥是旱地培肥土壤、提高水分生产效率的有效途径.     

Annual flower strips support pollinators and potentially enhance red clover seed yield

Ecological intensification provides opportunity to increase agricultural productivity while minimizing negative environmental impacts, by supporting ecosystem services such as crop pollination and biological pest control. For this we need to develop targeted management solutions that provide critical resources to service‐providing organisms at the right time and place. We tested whether annual strips of early flowering phacelia Phacelia tanacetifolia support pollinators and natural enemies of seed weevils Protapion spp., by attracting and offering nectar and pollen before the crop flowers. This was expected to increase yield of red clover Trifolium pratense seed. We monitored insect pollinators, pests, natural enemies and seed yields in a total of 50 clover fields along a landscape heterogeneity gradient, over 2 years and across two regions in southern Sweden. About half of the fields were sown with flower strips of 125–2,000 m². The clover fields were pollinated by 60% bumble bees Bombus spp. and 40% honey bees Apis mellifera. The clover seed yield was negatively associated with weevil density, but was unrelated to bee species richness and density. Flower strips enhanced bumble bees species richness in the clover fields, with the strongest influence in heterogeneous landscapes. There were few detectable differences between crop fields with and without flower strips. However, long‐tongued bumble bees were redistributed toward field interiors and during phacelia bloom honey bees toward field edges. Clover seed yield also increased with increasing size of the flower strip. We conclude that annual flower strips of early flower resources can support bumble bee species richness and, if sufficiently large, possibly also increase crop yields. However, clover seed yield was mainly limited by weevil infestation, which was not influenced by the annual flower strips. A future goal should be to design targeted measures for pest control.     

Canola and Oat Forage Potential Evaluation in Four Early Planting Dates

Canola and oat forage potential may be affected by climatic conditions when sown early. The objective of this study was to evaluate the forage canola and oat potential in four early sowing dates (September 11 and 25; October 9 and 23) during the 2012-2013 and 2013-2014 cycles in Matamoros, Coahuila, Mexico. Growth cycle duration, chemical composition, dry matter (DM), crude protein (CP), and net energy for lactation (NE_L) yields were determined. High temperatures and long photoperiods affected crops seeded on September 11, accelerating growth and reducing canola (26.6%-31.7%) and oat (15.8%) DM yields. As of September 25, canola cv IMC 205 reached DM yields (7746 kg ha^-1 -9276 kg ha^-1 ) similar to those obtained by oat (8115 kg ha^-1 -9507 kg ha^-1 ), while canola cv Hyola 401 obtained such yields only until October 23. Canola chemical composition was better than that found in oat, with higher CP, but lower acid detergent fiber (ADF) and neutral detergent fiber (NDF) contents. Canola equaled oat CP yields (972 kg ha^-1 -1215 kg ha^-1 ) in the first sowing date, while in the other three other canola sowings reached higher yields (1193 kg ha^-1 -1889 kg ha^-1 ). As for NEL yields, no difference was observed between both species. The best sowing date for canola is from September 25 on, with CP production advantages over oat.     

太湖地区两种稻麦轮作制中营养元素的循环——Ⅰ.稻麦作物内养分的移出与残留

本研究在基于乌栅土、黄泥土和鳝血白土的三组稻田生态系统设置稻麦两熟和稻稻麦三熟两种熟耕作制度、三种施肥处理(当地肥处理、无肥处理和有机肥处理)的田间试验,以试验小区为稻田生态系统的基本研究单位。在试验的第二轮作周期(1982年10月至1983年10月)内,试验结果表明,收获物对八种主要营养元素移出总量的高低顺序为 Si>N>K>P>Ca>S,Mg>Mn 硅的移出总量为230—650公斤硅/公顷,锰的移出量为1.5—9.5公斤锰/公顷;养分在田间的残留量占作物总吸收量的百分率(残留率)的大小顺序却为 Si,Mn,Ca>Mg,S>K,N,P 三组元素的平均残留率约分别为35％,25％和10％。施肥处理间作物的生物产量存在着差异。后季稻的谷物产量按高低顺序依次为有机肥处理,当地肥处理和无肥处理;其他各季作物则为当地肥,有机肥和无肥处理。一定时期内移出系统的收获物生物量占作物总生物产量的百分数(生物物质开放度)为70—90％,大部分初级生产物被移出系统。对营养元素在稻麦作物的籽粒、秸秆、残茬及根系等四部分的含量作主组元分析后,八营养元素依相互间的相关系数可分为四组:钾;氮和磷;硫和镁;钙、锰和硅。这与按残留率大小对元素所作的分组十分相似。因子分析表明,营养元素随收获物的携出量不仅直接受收获物生物量及其含量的影响,还与     

Meta-analysis of maize yield response to woody and herbaceous legumes in sub-Saharan Africa

A number of studies have tested the effect of woody and herbaceous legumes on soil fertility and maize yields in sub-Saharan Africa. However, their effects on maize productivity are much debated because results have been variable. A meta-analysis was conducted with the aim of evaluating the evidence in support of yield benefits from woody and herbaceous green manure legumes. A total of 94 peer-reviewed publications from West, East and southern Africa qualified for inclusion in the analysis. Maize yield from herbaceous green manure legumes (54 publications), non-coppicing legumes (48 publications), coppicing woody legumes (10 publications), natural fallows (29 publications), and fully fertilized monoculture maize (52 publications) were compared. Mixed linear modelling using yield differences (D) and response ratios (RR) indicated that the response to legumes is positive. The mean yield increase (D) over unfertilized maize was highest (2.3 t ha^?1) and least variable (CV?=?70%) in fully fertilized maize, while it was lowest (0.3 t ha^?1) and most variable (CV?=?229%) in natural fallows. The increase in yield over unfertilized maize was 1.6 t ha^?1 with coppicing woody legumes, 1.3 t ha^?1 with non-coppicing woody legumes and 0.8 t ha^-1 with herbaceous green manure legumes. Doubling and tripling of yields relative to the control (RR > 2) was recorded in coppicing species (67% of the cases), non-coppicing legumes (45% of the cases), herbaceous green manure legumes (16% of the cases) and natural fallows (19% of the cases). However, doubling or tripling of yields occurred only in low and medium potential sites. Amending post-fallow plots with 50% of the recommended fertilizer dose further increased yields by over 25% indicating that legume rotations may play an important role in reducing fertilizer requirements. Except with the natural fallow, the 95% confidence intervals of D and RR were higher than 1 and 0, respectively indicating significant and positive response to treatments. Therefore, it is concluded that the global maize yield response to legumes is significantly positive and higher than unfertilized maize and natural vegetation fallows.     

施肥对水稻产量和稻田土壤理化性质的影响

稻田土壤中养分的平衡主要取决于养分的输入与输出,其又主要受肥料的输入与植物所带走的养分所制约。不同的肥料品种、不同的施肥时期都影响养分在土壤中的吸收、转化与淋失,从而影响养分的输入与输出。稻田土壤生态系统中养分循环的研究已有很多报道。主要是不同耕作制度、不同施肥水平下,各输入输出因子的研究以及对土壤肥     

Comparing annual and perennial crops for bioenergy production – influence on nitrate leaching and energy balance

Production of energy crops is promoted as a means to mitigate global warming by decreasing dependency on fossil energy. However, agricultural production of bioenergy can have various environmental effects depending on the crop and production system. In a field trial initiated in 2008, nitrate concentration in soil water was measured below winter wheat, grass‐clover and willow during three growing seasons. Crop water balances were modelled to estimate the amount of nitrate leached per hectare. In addition, dry matter yields and nitrogen (N) yields were measured, and N balances and energy balances were calculated. In willow, nitrate concentrations were up to approximately 20 mg l^?1 nitrate‐N during the establishment year, but declined subsequently to <5 mg l^?1 nitrate‐N, resulting in an annual N leaching loss of 18, 3 and 0.3 kg ha^?1 yr^?1 N in the first 3 years after planting. A similar trend was observed in grass‐clover where concentrations stabilized at 2–4 mg l^?1 nitrate‐N from the beginning of the second growing season, corresponding to leaching of approximately 5 kg ha^?1 yr^?1 N. In winter wheat, an annual N leaching loss of 36–68 kg ha^?1 yr^?1 was observed. For comparison, nitrate leaching was also measured in an old willow crop established in 1996 from which N leaching ranged from 6 to 27 kg ha^?1 yr^?1. Dry matter yields ranged between 5.9 and 14.8 Mg yr^?1 with lowest yield in the newly established willow and the highest yield harvested in grass‐clover. Grass‐clover gave the highest net energy yield of 244 GJ ha^?1 yr^?1, whereas old willow, winter wheat and first rotation willow gave net energy yields of 235, 180 and 105 GJ ha^?1 yr^?1. The study showed that perennial crops can provide high energy yields and significantly reduce N losses compared to annual crops.     

Green manure technology: Potential,usage, and limitations. A case study for lowland rice

The growing concern about the sustainability of tropical agricultural systems stands in striking contrast to a world-wide decline in the use of soil-improving legumes. It is timely to assess the future role that soil-improving legumes may play in agricultural systems. This paper reviews recent progress, potential, and limitations of green manure technology, using lowland rice cropping systems as the example.Only a few legume species are currently used as green manures in lowland rice. Sesbania cannabina is the most widely used pre-rice green manure for rice in the humid tropics of Africa and Asia. Astragalus sinicus is the prototype post-rice green manure species for the cool tropics. Stem-nodulating S. rostrata has been most prominent in recent research. Many green manure legumes show a high N accumulation (80–100 kg N ha^-1 in 45–60 days of growth) of which the major portion (about 80%) is derived from biological N₂ fixation. The average amounts of N accumulated by green manures can entirely substitute for mineral fertilizer N at current average application rates. With similar N use efficiencies, green manure N is less prone to loss mechanisms than mineral N fertilizers and may therefore contribute to long-term residual effects on soil productivity.Despite a high N₂-fixing potential and positive effects on soil physical and chemical parameters, the use of green manure legumes for lowland rice production has declined dramatically world-wide over the last 30 years. Land scarcity due to increasing demographic pressure and a relatively low price of urea N are probably the main determining factors for the long-term reduction in pre-rice green manure use. Post-rice green manures were largely substituted for by high-yielding early-maturing grain legumes. Unreliability of green manure performance, non-availability of seeds, and labor intensive operations are the major agronomic constraints. The recognition and extrapolation of niches where green manures have a comparative advantage may improve an often unfavorable economic comparison of green manure with cash crop or fertilizer N. Socio-economic factors like the cost of land, labor, and mineral N fertilizer are seen to determine the cost-effectiveness and thereby farmers' adoption of sustainable pre-rice green manure technology. Hydrology and soil texture determine the agronomic competitiveness of a green manure with N fertilizers and with alternative cash crops. In general, the niches for pre-rice green manure are characterized by a relatively short time span available for green manure growth and a soil moisture regime that is unfavorable for cash crops (flood-prone rainfed lowlands with coarse-textured soils).Given the numerous agronomic and socio-economic constraints, green manure use is not seen to become a relevant feature of favourable rice-growing environments in the foreseeable future. However, in environments where soil properties and hydrology are marginal for food crop production, but which farmers may be compelled to cultivate in order to meet their subsistence food requirements, green manures may have a realistic and applicable potential.     

The effect of stem nematode on establishment and early yields of white clover

The effects of stem nematode (Ditylenchus dipsaci) infestation on the establishment of white clover sown in mixed swards with perennial ryegrass, were investigated in two field trials. Clover cultivars known to have different degrees of resistance were sown on land in which stem nematode was controlled either by aldicarb (Experiment 1) or crop rotation (Experiment 2). The establishment of white clover was greatly improved and subsequent clover yields were inversely related to stem nematode infestation. At the first harvest after sowing, clover yields were 3.6 and 3.3 times greater from aldicarb and rotation treatment plots than from check plots; over the first nine months, total clover yields were increased by 3.5 and 8.9 times by aldicarb and rotation treatments. In both trials, plots of resistant cultivars had less stem nematode infestation and yielded better than the very susceptible cultivar, S184. Stem nematode infestations eventually developed on all plots, after the establishment phase. This is the first report showing that resistant cultivars improve establishment of clover in mixed swards on stem nematode infested soils. In both experiments, plots became dominated by clover and even cv. S184 eventually produced good clover swards. Aldicarb and rotation treatments also controlled clover cyst and root lesion nematodes, and numbers of these were inversely related to first harvest yields. Other soil borne pests and diseases, although not prominent, have not been ruled out as possible confounding factors. There was no correlation between grass yield and aldicarb treatment.     

不同培肥措施对红壤茶园土壤微生物量碳的影响

研究了经过4年不同培肥措施后红壤茶园土壤微生物量碳变化.结果表明:稻草覆盖后不同比例有机无机肥配施、间作三叶草以及全施化肥处理对土壤微生物量碳均有明显提高;全年土壤微生物量碳年变化都呈现"低-高-低-高"的趋势,且在不同时期对微生物量碳的影响不同;与对照(CK)相比,稻草覆盖 100%有机肥(T1)、稻草覆盖 75%有机肥 25%化肥(T2)、稻草覆盖 50%有机肥 50%化肥(T3)、稻草覆盖 25%有机肥 75%化肥(T4)、100%化肥(T5)和间作三叶草 不施肥(T6)土壤微生物量碳全年平均值分别高出17.05%、32.38%、32.05%、24.30%、26.23%和24.63%,且差异均达到显著水平(P＜0.05);土壤微生物量碳与活性有机质、土壤全氮、微生物量氮、微生物量磷呈显著正相关,与速效氮、土壤全磷、土壤全钾、土壤含水量之间关系不显著;与单施化肥和全量投入有机物料相比,有机物和化肥配合施用更有利于提高土壤肥力.     

Natural endophytic association between Rhizobium leguminosarum bv. trifolii and rice roots and assessment of its potential to promote rice growth

For over 7 centuries, production of rice (Oryza sativa L.) in Egypt has benefited from rotation with Egyptian berseem clover (Trifolium alexandrinum). The nitrogen supplied by this rotation replaces 25- 33% of the recommended rate of fertilizer-N application for rice production. This benefit to the rice cannot be explained solely by an increased availability of fixed N through mineralization of N- rich clover crop residues. Since rice normally supports a diverse microbial community of internal root colonists, we have examined the possibility that the clover symbiont, Rhizobium leguminosarum bv. trifolii colonizes rice roots endophytically in fields where these crops are rotated, and if so, whether this novel plant-microbe association benefits rice growth. MPN plant infection studies were performed on macerates of surface-sterilized rice roots inoculated on T. alexandrinum as the legume trap host. The results indicated that the root interior of rice grown in fields rotated with clover in the Nile Delta contained 10⁶ clover-nodulating rhizobial endophytes g fresh weight of root. Plant tests plus microscopical, cultural, biochemical, and molecular structure studies indicated that the numerically dominant isolates of clover-nodulating rice endophytes represent 3 – 4 authentic strains of R. leguminosarum bv. trifolii that were Nod Fix on berseem clover. Pure cultures of selected strains were able to colonize the interior of rice roots grown under gnotobiotic conditions. These rice endophytes were reisolated from surface-sterilized roots and shown by molecular methods to be the same as the original inoculant strains, thus verifying Koch's postulates. Two endophytic strains of R. leguminosarum bv. trifolii significantly increased shoot and root growth of rice in growth chamber experiments, and grain yield plus agronomic fertilizer N-use efficiency of Giza-175 hybrid rice in a field inoculation experiment conducted in the Nile Delta. Thus, fields where rice has been grown in rotation with clover since antiquity contain Fix strains of R. leguminosarum bv. trifolii that naturally colonize the rice root interior, and these true rhizobial endophytes have the potential to promote rice growth and productivity under laboratory and field conditions.     

Plow down effects of different forage legume species,cultivars, cutting strategies and seeding rates on the yields of subsequent crops

Summary Under some conditions the plow down of forage legumes increases the yield of subsequent crops, which is usually caused by improved soil N. However, better soil structure is also a contributing factor. Three experiments were conducted to measure the effect of legume plow down on the yield of subsequent corn crops grown at the Ottawa Research Station (ORS), Ottawa, Canada. In all experiments, corn yields were not affected by legume species, legume cultivars, and/or planting methods. Corn yields from barley plots receiving 0, 60, or 120 kg N ha⁻¹ did not differ until two years after establishment in one experiment and three years in another. The data from these experiments indicated that soil N was high at the ORS, which may inhibit N₂-fixation by forage legumès in the establishment year. Therefore, legume plow down was not beneficial to subsequent crops under these conditions. Two other experiments were conducted to measure the effect of legume plow down on the yield of subsequent barley crops. In both experiments, barley yields in the field were not affected by legume type or legume seeding density. Greenhouse and field data indicated that the two cuts with removal strategy benefitted the most to succeeding crops. Data from the greenhouse test indicated that soil N levels were not low in the establishment year, and that some cultivars improved soil fertility more than others.     

Switchgrass Biofuel Production on Reclaimed Surface Mines: I. Soil Quality and Dry Matter Yield

Growing food crops for biofuel on productive agricultural lands may become less viable as requirements to feed a growing human population increase. This has increased interest in growing cellulosic biofuel feedstocks on marginal lands. Switchgrass (Panicum virgatum L.), a warm-season perennial, is a viable bioenergy crop candidate because it produces high yields on marginal lands under low fertility conditions. In other studies, switchgrass dry matter (DM) yields on marginal croplands varied from 5.0 to 10.0 Mg ha^?1 annually. West Virginia contains immense areas of reclaimed surface mined lands that could support a switchgrass-based biofuel industry, but yield data on these lands are lacking. Field experiments were established in 2008 to determine yields of three switchgrass cultivars on two West Virginia mine sites. One site reclaimed with topsoil and municipal sludge produced biomass yields of 19.0 Mg DM ha^?1 for Cave-in-Rock switchgrass after the sixth year, almost double the varieties Shawnee and Carthage, at 10.0 and 5.7 Mg ha^?1, respectively. Switchgrass yields on another site with no topsoil were 1.0 Mg ha^?1 after the sixth year, with little variation among cultivars. A second experiment was conducted at two other mine sites with a layer of topsoil over gray overburden. Cave-in-Rock was seeded with fertilizer applications of 0, 34, and 68 kg N-P₂O₅-K₂O ha^?1. After the third year, the no fertilizer treatment averaged biomass yields of 0.3 Mg ha^?1, while responses to the other two rates averaged 1.1 and 2.0 Mg ha^?1, respectively. Fertilization significantly increased yields on reclaimed mine soils. Where mine soil fertility was good, yields were similar to those reported on agricultural soils in the Northeastern USA.