Replication data for: Prototype hedgegrow intercropping systems

Farmers' maize (Zea mays) yields in semiarid Kenya are low because of low and erratic rainfall and soil nutrient depletio
n. An experiment was conducted in Machakos, Kenya, during November 1989–July 1995 to explore the potential of hedgerow intercropping (HI) with Leucaena leucocephala as an alternative strategy to the use of inorganic fertilizers for improving maize yields in semiarid bimodal highlands. The study, conducted in a randomized block design with three replications, evaluated on an operational scale with four treatments: sole maize with or without fertilizer; and HI with prunings of L. leucocephala hedges used as green manure or with prunings and maize stover fed to oxen and manure returned to soil. About 1.4 t ha−1 of L. leucocephala foliar biomass and 1.2 t ha−1 manure were incorporated each season in green-manure and ox-manure systems, respectively. Although sole maize responded to inorganic fertilizer in six of 11 seasons, maize yield was improved by HI, with prunings used as green manure, only once, 5 yrs after the commencement of the study, when rainfall exceeded 500 mm. Over the experimental period, maize yields were 15% and 30% less in green-manure and ox-manure systems, respectively, than in unfertilized maize, primarily because of the competition of hedgerows with crops for water. The fodder system of HI recycled only 27% of N and 50% of P exported from the field in fodder, grain and stover, and depleted nutrients more than the other systems. The green-manure system made a positive N balance, with similar P depletion as in the fodder system. No changes were detected in soil organic carbon or cations in any of the systems during the experimental period while extractable P was significantly improved by fertilizing maize. Net present value of returns from fertilizing maize at 40 kg N and 18 kg P ha−1 was 10% higher than from the unfertilized control. Fertilizer use would be 25% more profitable, however, if P were applied only to match the amount of P removed by crop (9 kg P ha−1 per season) and if maize were not topdressed (amounting to 50% of the recommended N) in poor rainfall seasons. Of the two HI systems, only the fodder system was more profitable than either system of sole-cropped maize because the high value of fodder more than compensated the smaller maize yield obtained in HI. However, the fodder system may not give higher economic returns than a sole L. leucocephala fodder bank. Hence, HI using competitive species such as L. leucocephala and with the level of productivity observed in this study, is not appropriate for semiarid climates to increase cereal yields, either directly through green manuring or indirectly by fodder production and nutrient cycling through livestock.

肯尼亚半干旱地区农户的玉米（Zea mays）产量偏低，其成因包括降雨稀少且波动不定，以及土壤养分耗竭。本研究于1989年11月至1995年7月在肯尼亚马查科斯开展田间试验，旨在探究树篱间作（hedgerow intercropping, HI）配合银叶合欢（Leucaena leucocephala）的应用潜力，以此作为无机肥料的替代方案，提升半干旱双季高地的玉米产量。本研究采用随机区组设计，设置3次重复，在实际作业尺度下评估4种处理模式：单作玉米配施或不配施无机化肥；以及树篱间作体系，分别以银叶合欢树篱修剪物作为绿肥还田，或将修剪物与玉米秸秆饲喂耕牛，再将畜禽粪便归还土壤。绿肥体系每季约施入1.4吨/公顷的银叶合欢叶片生物量，畜禽粪便体系则每季施入1.2吨/公顷的粪便。尽管11个生长季中有6个季的单作玉米产量对无机化肥产生响应，但采用修剪物作为绿肥的树篱间作体系仅在试验启动5年后、降雨量超过500毫米的一个季次中实现了玉米产量提升。试验周期内，绿肥体系与畜禽粪便体系的玉米产量分别较不施肥单作玉米低15%与30%，核心原因是树篱与作物竞争水分资源。树篱间作的饲料体系仅回收了籽粒、秸秆与饲料中携出的27%的氮与50%的磷，养分耗竭程度高于其他处理模式。绿肥体系实现了正的氮素平衡，磷素耗竭程度则与饲料体系相当。试验期间，各体系的土壤有机碳与阳离子含量均未检测到显著变化，但配施化肥可显著提升土壤有效磷含量。施入40千克氮与18千克磷/公顷的玉米施肥处理，其净现值（net present value）较不施肥对照高10%。不过，若仅按照作物携出的磷量（每季9千克磷/公顷）施用磷肥，且在降雨偏少的季次不追施氮肥（相当于推荐施氮量的50%），化肥使用的盈利性可提升25%。在两种树篱间作体系中，仅饲料体系的盈利性高于两种单作玉米处理，因为饲料的高价值弥补了玉米产量的损失。然而，饲料体系的经济收益未必高于单纯种植银叶合欢作为饲料储备库的模式。综上，采用银叶合欢这类竞争性物种、且达到本研究观测到的生产力水平的树篱间作体系，并不适用于半干旱气候区，既无法通过绿肥直接提升谷物产量，也无法通过饲料生产与畜禽养分循环间接实现增产。