Soil properties, grassland management, and landscape diversity drive the assembly of earthworm communities in temperate grasslands

Earthworms are widespread soil organisms that contribute to a wide range of ecosystem services. As such, it is important to improve our knowledge, still scanty, of the factors that drive the assembly of earthworm communities. The aim of the present study was to conjointly evaluate the effects on the assembly of earthworm communities of i) soil properties (texture, organic matter content, and pH), ii) grassland management (grassland age, livestock unit, and type of fertilization), iii) landscape diversity (richness, diversity of surrounding habitats, and grassland plant diversity), and iv) presence of hedgerows. The study was conducted in temperate grasslands of Brittany, France. Earthworms were sampled in 24 grasslands and, in three of these grasslands, they were sampled near a hedgerow or near a ditch (control without a hedgerow). Soil properties explained the larger portion of the variation in the earthworm community parameters compared to grassland management or landscape diversity. The increase in soil organic matter content and pH were the most favorable factors for earthworm abundance and biomass, in particular for endogeic species. Regarding grassland management, the increase in the livestock unit was the most damaging factor for earthworm communities, in particular for the anecic earthworm biomass and endogeic species richness. Surprisingly, landscape diversity negatively affected the total earthworm abundance and epigeic earthworm biomass, but it was related to an increase in the epi-anecic species. At a finer scale, we also demonstrated that the presence of hedgerows surrounding grasslands enhanced earthworm species richness, especially within the epigeic and anecic ecological categories. This study highlights that the earthworm ecological categories respond specifically to environmental filters; further studies need to be conducted to elucidate the factors that drive the assembly of earthworm communities at this ecological category level. We recommend that policymakers should act on landscape management to favor earthworm diversity in order to improve the ecosystem services they drive.     

坡耕地植物篱在水土保持中的应用

 坡耕地植物篱种植模式是一种坡耕地可持续利用技术。结合已有研究成果,对坡耕地植物篱研究现状、效益等作了系统介绍。植物篱种植模式对改善土壤物理性质、提高土壤养分、减小坡耕地水土流失、防止土壤退化、促进农作物生长、增加作物产量、提供饲料、薪柴等方面具有良好的作用和效果,植物篱在坡耕地资源可持续利用中具有显著的生态效益和经济效益。对目前坡耕地植物篱认识上的问题及需要深入开展的工作进行了讨论,以促进我国植物篱技术和坡耕地整治的研究与发展。     

等高绿篱——坡地农业复合系统土壤性质空间变异

土壤性质空间变异是一种普遍现象,但等高绿篱——坡地农业复合系统中土壤性质空间变异的研究较少。本文以设置在三峡库区王家桥小流域的香根草（Vetiveria zizanioides）绿篱试验小区为研究对象,从径流小区尺度探讨了不同措施对土壤性质空间变异的影响。结果表明,绿篱种植可降低O．2～0．002mm粒级团聚体的空间变...     

A tree/crop interface design and its use for evaluating the potential of hedgerow intercropping

The paper describes a tree/crop interface (TCI) experiment designed to investigate the effects of row orientation using Leucaena leucocephala Lam. Each TCI plot consisted of a regularly pruned Leucaena hedge in the middle and 12 crop rows on either side. Eight such plots were arranged at 45° around a sole Leucaena plot with rows oriented in four compass directions viz., North-South, East-West, Northeast-Southwest and Northwest-Southeast.Results of four years from 1984 to 1987 did not show any effect of row orientation, and similarly, no effect was seen on crop rows due to their location on the windward or leeward side of the hedge. The TCI effect was positive on the first crop row in the first year because Leucaena grew slowly, but depressed the yield of the first 4 to 6 crop rows(1.8 to 2.7 m from hedge) in subsequent years. The negative effect of Leucaena was noted more on sunflower in a relatively dry year than on sorghum in other years.Results from the TCI plots were used to estimate the yield of five hedgerow intercropping (HI) systems with varying alley widths (2.7 to 9.9 m). Comparison with sole stands of Leucaena and crops indicated that HI was more productive particularly at close alley widths. For example, hedges spaced at 2.7 m and 3.6 m averaged 37% and 25% higher productivity than the respective sole stands; but this advantage may be an overestimation of the real potential.The relevance of TCI experiments for studying agroforestry systems, their merits and limitations, especially of the design employed in this study are discussed.     

Alley cropping maize (Zea mays var.Jeka) with cassia (Cassia siamea) in The Gambia: crop production and soil fertility

The relative contributions of cassia prunings and inorganic fertilizer to yield of maize (number of ears and weight of grain, ears, cobs and stover), maize grain quality (weight of 3 largest size fractions) and soil pH, N, P, K and organic matter contents were investigated at a semi-arid site in The Gambia. Four treatments: control (no prunings or fertilizer applied), only prunings applied, prunings plus half the recommended rate of fertilizer, and the full recommended fertilizer rate plus prunings, were replicated in a Latin square design. At the full fertilizer rate, 125 kg/ha of NPK (82424) plus 43.5 kg/ha urea was broadcast at the time of sowing followed by 100 kg/ha of urea applied as side dressing two weeks after crop germination. Soil N, P, K organic matter and pH were not significantly different either before cropping or after crop harvest in both 0–10 and 10–15 cm soil depth.Crop yield, as measured by number and dry weight of ears, stover, grain and cob weights, was significantly different among treatments (p=0.0001, p=0.0001, p=0.0001, p=0.0001 and p=0.0001, respectively). The application of prunings plus full recommended fertilizer produced the highest yields. The weights of the three largest grain size fractions, grades A, B, and C, differed significantly between treatments (p=0.0026, p=0.0001 and p=0.0001, respectively). Yield of grade A grain increased by 202% over control with application of prunings plus full rate fertilizer and declined by 31% relative to the control with application of only prunings. More grade A, B and C grain was produced with application of full rate fertilizer plus prunings than in control treatments. However, application of half rate fertilizer plus prunings produced a higher proportion of grade A grain.     

Productivity of annual cropping and agroforestry systems on a shallow Alfisol in semi-arid India

An experiment was conducted at ICRISAT Center, Patancheru, India from June 1984 to April 1988 on a shallow Alfisol to determine whether the productivity of annual crop systems can be improved by adding perennial species such as Leucaena leucocephala managed as hedgerows. Except in the first year, crop yields were suppressed by Leucaena due to competition for moisture. The severity of competition was high in years of low rainfall and on long-duration crops such as castor and pigeonpea. Based on total biomass, sole Leucaena was most productive; even on the basis of land productivity requiring both Leucaena fodder and annual crops, alley cropping had little or no advantage over block planting of both components. Application of hedge prunings as green manure or mulch on top of 60 kg N and 30 kg P ₂ O ₅ha⁻¹ to annual crops did not show any benefit during the experimental period, characterized by below average rainfall. Indications are that (i) alley cropping was beneficial in terms of soil and water conservation with less runoff and soil loss with 3 m alleys than with 5.4 m alleys, and (ii) root pruning or deep ploughing might be effective in reducing moisture competition.     

A knowledge-based expert system for planning and design of agroforestry systems

Computer-based Expert Systems that use knowledge, facts, and reasoning techniques to solve problems, normally requiring the abilities of human experts, are increasingly being used in many activities. The United Nations University (UNU) Agroforestry Expert System (AES) is a first attempt to apply this technique to agroforestry. UNU-AES is a prototype Knowledge-Based Expert System (KBES) designed to support land-use (agricultural, forestry, etc.) officials, research scientists, farmers, and individuals interested in maximizing benefits gained from applying agroforestry management techniques in developing countries. This prototype addresses the options for alley cropping, a promising agroforestry technology which has potential applicability when used under defined conditions in the tropics and subtropics. Alley cropping involves the planting of crops in alleys or interspaces between repeatedly pruned hedgerows of fast-growing, preferably leguminous, woody perennials. The primary benefits from this technique include nutrient enrichment, soil improvement, and erosion control. UNU-AES, which is the first known attempt at the application of expert system procedures in the field of agroforestry, uses a total of 235 decision rules to develop its recommendations. With the inclusion of more climatic and socio-economic data and improved advisory recommendations, UNU-AES can be expanded to provide advice on alley cropping in more diverse geographical and ecological conditions and eventually address other agroforestry techniques.     

Alley cropping rice (Oryza sativa var.Barafita) with cassia (Cassia siamea): soil fertility and crop production

Rice grain weight and quality (weight of larger size fractions), soil pH, and N, P, K and organic matter content were studied where rice was alley cropped with cassia on a semiarid site in The Gambia. The four treatments, control (no cassia prunings or inorganic fertilizer added), only prunings added, prunings plus half the recommended fertilizer rate and prunings plus full recommended rate of fertilizer, were applied in a Latin square design with 10×8 m plots, each sub-divided into two 4-m wide alleys. Fertilizer was applied twice; full rates were 93.7 kg/ha NPK (8:24:24) plus 32.4 kg/ha urea followed two weeks later by 100 kg/ha urea applied as side dressing. Soil samples collected before and after cropping at 0–10 cm and 10–15 cm depths and cassia pruning samples were analyzed for pH, N, P, K and organic matter content.Our results do not show significant benefit of cassia prunings applied as mulch to grain weight or quality in alley cropping rice with cassia. The addition of inorganic fertilizer plus cassia prunings did not increase rice grain and straw weights (p=0.3447 and p=0.0691, respectively) compared to the control and prunings only treatments. In all treatments, the outer rows, those within 80 cm of hedgerows, produced significantly less grain (p=0.0002) and straw than inner rows. Neither the larger grade A nor the smaller grade B grain weights were significantly different (p=0.6017 and p=0.0629, respectively) between treatments. Weight of grain, straw, and larger grade A and smaller grade B quality grain did not differ significantly for inner and outer rows (p=0.6329, p=0.7148, p=0.7171 and p=1.000, respectively).     

The potential of alley farming in humid West Africa — a re-evaluation

Previously published hypothesis concerning the potential impact of alley farming on maize yields are re-examined relative to the humid regions of West Africa. When more realistic assumptions regarding the availability of organic nitrogen are used, it is concluded that alley farming may have potential in a wider range of maize yield environments in West Africa than previously proposed. A pragmatic approach to alley farming research is proposed, and the importance of on-farm research in the development of farmer friendly alley farming is stressed.(Former Agronomist, International Livestock Centre for Africa, P.M.B. 5320, Ibadan, Nigeria)     

Biophysical interactions in tropical agroforestry systems

The rate and extent to which biophysical resources are captured and utilized by the components of an agroforestry system are determined by the nature and intensity of interactions between the components. The net effect of these interactions is often determined by the influence of the tree component on the other component(s) and/or on the overall system, and is expressed in terms of such quantifiable responses as soil fertility changes, microclimate modification, resource (water, nutrients, and light) availability and utilization, pest and disease incidence, and allelopathy. The paper reviews such manifestations of biophysical interactions in major simultaneous (e.g., hedgerow intercropping and trees on croplands) and sequential (e.g., planted tree fallows) agroforestry systems. In hedgerow intercropping (HI), the hedge/crop interactions are dominated by soil fertility improvement and competition for growth resources. Higher crop yields in HI than in sole cropping are noted mostly in inherently fertile soils in humid and subhumid tropics, and are caused by large fertility improvement relative to the effects of competition. But, yield increases are rare in semiarid tropics and infertile acid soils because fertility improvement does not offset the large competitive effect of hedgerows with crops for water and/or nutrients. Whereas improved soil fertility and microclimate positively influence crop yields underneath the canopies of scattered trees in semiarid climates, intense shading caused by large, evergreen trees negatively affects the yields. Trees in boundary plantings compete with crops for above- and belowground resources, with belowground competition of trees often extending beyond their crown areas. The major biophysical interactions in improved planted fallows are improvement of soil nitrogen status and reduction of weeds in the fallow phase, and increased crop yields in the subsequent cropping phase. In such systems, the negative effects of competition and micro-climate modification are avoided in the absence of direct tree–crop interactions. Future research on biophysical interactions should concentrate on (1) exploiting the diversity that exists within and between species of trees, (2) determining interactions between systems at different spatial (farm and landscape) and temporal scales, (3) improving understanding of belowground interactions, (4) assessing the environmental implications of agroforestry, particularly in the humid tropics, and (5) devising management schedules for agroforestry components in order to maximize benefits. This revised version was published online in June 2006 with corrections to the Cover Date.