Soil erosion and land fragmentation threaten agricultural production of sub-Saharan African highlands. At our study site in Western Kenya, farm size is mostly < 2 ha, laid out in narrow strips in slope direction and ploughed downhill. Soil conservation measures like hedgerows and green manures can reduce effective slope length for erosion, but compete with crops for space and labour. Knowledge of critical slope length can minimise interventions and trade–offs. Hence, a maize–bean intercrop (MzBn) slope length trial on 20, 60 and 84 m long plots, replicated twice on three farms was carried out in Rongo, Migori County, during one rainy season. Soil loss from 84 m slope length (SL) plots was 250 % higher than from 60 m and 710% higher than from 20 m plots, while soil loss from 20 and 60 m plots did not differ (p < 0.05). Conversely, runoff was lower on the 84 m than on the 60 m (p < 0.05) or the 20 m SL (p < 0.05). Across all three farms slope gradient and length had highest explanatory power to predict soil loss. At individual farm level, under similar slope and soil texture, slope length and profile curvature were most influential. Regarding results of the slope length experiments, food crop plot lengths < 50 m appear essential considering soil loss, sediment load, and soil loss to yield ratio under the given rainfall, soil and slope (10–14%) conditions. Our results call for designing integrating slope length options and cropping systems for effective soil conservation. We recommend planting Mucuna and Calliandra–hedgerows as buffer strips below the critical slope length, and legume cash crops and maize uphill. Such approaches are critical against the backdrop of land fragmentation and labour limitation to sustainably maximise food production from the available land area in the region.

水土流失和土地破碎化威胁着撒哈拉以南非洲高地的农业生产。在我们位于肯尼亚西部的研究场地中，农场规模通常小于2公顷，在坡度方向上呈窄条状布置，并下坡耕作。诸如树篱和绿肥这样的土壤保护措施可以减少有效的边坡长度以进行侵蚀，但可以与作物竞争空间和劳力。了解临界边坡长度可以最大程度地减少干预和权衡取舍。因此，在一个雨季期间，在Migori县的Rongo进行了玉米，大豆间作（MzBn）边坡长度试验，试验长度为20、60和84 m，在三个农场重复了两次。84 m坡长（SL）样地的土壤流失比60 m地块高250％，比20 m地块高710％，而20和60 m地块的土壤流失没有差异（p <0.05）。反过来，84 m的径流比60 m（p <0.05）或20 m SL（p <0.05）低。在所有三个农场中，坡度和坡度对预测土壤流失具有最高的解释力。在单个农场级别，在相似的坡度和土壤质地下，坡度长度和剖面曲率影响最大。关于边坡长度实验的结果，在给定的降雨，土壤和坡度（10％至14％）条件下，考虑到土壤流失，沉积物负荷以及土壤流失与产量之比，<50 m的粮食作物田间长度显得至关重要。我们的结果要求设计整合坡度长度选项和耕作系统的有效土壤保护措施。我们建议在临界边坡长度以下种植Mucuna和Calliandra-树篱作为缓冲带，并种植豆类经济作物和玉米。