Agro-economic benefits in radish-lettuce intercropping under optimized green manuring and planting density

ABSTRACT One of the biggest difficulties in the intercropping of radish-lettuce is to obtain the ideal dose of green manure and the adequate planting density for the crops. Therefore, the objective of the present work was to evaluate the agro-economic benefits of radish-lettuce intercropping under the influence of green manuring with Merremia aegyptia (hairy woodrose) and Calotropis procera (roostertree) and lettuce population densities in a semi-arid environment, in two cropping seasons. The experimental design used was randomized blocks, with treatments arranged in a 4x4 factorial scheme, with 4 replicates. The first factor in this scheme consisted of equitable biomass amounts of M. aegyptia and C. procera at doses of 20, 35, 50 and 65 t/ha on a dry basis, and the second factor of lettuce population densities of 150, 200, 250 and 300 thousand plants/ha. The production of radish and lettuce and its components, in addition to the agroeconomic indicators, system productivity index (SPI), land equivalent coefficient (LEC) and monetary equivalent ratio (MER) were evaluated. The greatest agro-economic benefits of the intercropped radish-lettuce were obtained with SPI of 15.37 t/ha, LEC of 1.27 and MER of 1.30, respectively, in the combination of 65 t/ha of M. aegyptia and C. procera biomass with the lettuce population density of 300 thousand plants/ha. The maximum commercial productivity of radish roots in the intercropping system was 8.45 t/ha in the combination of the biomass amount of 20 t/ha of M. aegyptia and C. procera and lettuce population density of 300 thousand plants/ha, while the maximum lettuce leaf productivity optimized in intercropping was 17.72 t/ha, in the combination of green manures biomass amount of 65 t/ha and population density of 300 thousand plants/ha of lettuce. The use of spontaneous species from the Caatinga biome as green manure in the radish-lettuce intercropping provides optimized agro-economic benefits in a semi-arid environment.

摘要 萝卜-生菜间作的核心挑战之一，是确定作物理想的绿肥施用量与适宜种植密度。为此，本研究旨在评估半干旱环境下两个种植季中，银背藤（Merremia aegyptia，hairy woodrose）与牛角瓜（Calotropis procera，roostertree）绿肥还田，以及生菜种植密度对萝卜-生菜间作农艺经济效益的影响。
本研究采用随机区组设计，处理组按4×4析因方案设置，共4次重复。该析因方案的第一个因子为干重基施用量分别为20、35、50、65 t/ha的等生物量银背藤与牛角瓜，第二个因子为生菜种植密度15、20、25、30万株/公顷。本研究测定了萝卜与生菜的产量及其构成因子，同时评估了农经指标、系统生产力指数（system productivity index, SPI）、土地当量系数（land equivalent coefficient, LEC）与货币当量比（monetary equivalent ratio, MER）。
研究结果显示，当施用65 t/ha的银背藤与牛角瓜生物量，且生菜种植密度为30万株/公顷时，间作系统的农艺经济效益最优，此时系统生产力指数达15.37 t/ha，土地当量系数为1.27，货币当量比为1.30。间作系统中萝卜块根的最大商品产量为8.45 t/ha，对应处理组合为20 t/ha的银背藤与牛角瓜生物量施用量、生菜种植密度30万株/公顷；而生菜叶片的最高优化产量为17.72 t/ha，对应处理组合为65 t/ha的绿肥生物量施用量与30万株/公顷的生菜种植密度。
将卡廷加生物群系的本土自发物种作为绿肥应用于萝卜-生菜间作，可在半干旱环境中实现优化的农艺经济效益。