Cropping system

Biology

Nitrogen

Soil water

Crop

Organic chemistry

Nitrogen cycle

Agronomy

Legume

Intercropping

Environmental science

Soil science

Nitrogen balance

Chemistry

Soil fertility

Dolichos

Mineralization (soil science)

Leaching (pedology)

Nutrient Cycling in Agroecosystems

Negative nitrogen balance represents a major factor causing low potato yield in potato growing areas of Kenya while its excessive surplus poses a significant environmental concern. In order to synchronize this tradeoff, a field trial integrating potato ( Solanum tuberosum L.) with lima bean ( Phaseolus lunatus L.) and dolichos ( Lablab purpureus L.) in intercropping system was conducted in the upper midland [1552 m above sea level (masl), lower highland (1894 masl) and upper highland (2552 masl)] agro-ecological zones of Kenya. Nitrogen gains from mineralization, fertilization, biological fixation, and outputs from biomass accumulation, leaching, volatilization and soil erosion were quantified using standard procedures. Soil N balance ranged from − 10.7 to − 18.1 kg N ha −1 for sole potato, 4.1 to 6.6 kg N ha −1 for intercropping and 2.9 to 22.3 kg N ha −1 for sole legumes. The intermediate range of polyphenol and lignin contents in intercropping enhanced N mineralization with peak N release of 8 to 9 kg N ha −1 matching with peak N uptake by potato (19.9 to 31.2 kg N ha −1 ). Nitrate was leached below the active root zone in sole potato cropping (4.2 to 46.6 kg N ha −1 ), a process that was diverged by the deep root systems of legume intercrops. These results suggest that legume intercropping can provide a means of balancing the nitrogen retained in the biomass and soil, thus offering a mechanism for optimizing the soil N balance in smallholder potato farming systems.

Optimizing soil nitrogen balance in a potato cropping system through legume intercropping