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Nitrogen release and synchrony in organic and conventional farming systems of the Central Highlands of Kenya

Musyoka, Martha W., Adamtey, Noah, Bünemann, Else K., Muriuki, Anne W., Karanja, Edward N., Mucheru-Muna, Monica, Fiaboe, Komi K. M., Cadisch, Georg
Nutrient cycling in agroecosystems 2019 v.113 no.3 pp. 283-305
bags, composts, corn, green leafy vegetables, highlands, irrigation, nitrogen, pesticides, planting, potatoes, tubers, Kenya
To match Nitrogen (N) supply to crop N demand, it is essential to understand N release and uptake patterns in different farming systems and crops. To assesses the dynamics of N released in organic and conventional systems and potential synchrony and asynchrony in crop N uptake, a study was conducted over three cropping seasons (potato, maize and leafy vegetables) at two sites in the Central Highlands of Kenya. Mineral-N release and synchrony were monitored in conventional and organic systems at high (recommended N, P, pesticides and irrigation) and low input (low N, P, pesticide use and rainfed) systems. Mineral-N release was assessed using in situ buried bags and N synchrony was measured by the daily differences in N fluxes. The percentage of N applied released during potato (38%) and vegetable (44%) cropping seasons were similar between systems. However, under maize strong temporal N immobilization from inputs occurred, particularly at Thika, related to the poor quality of manure and compost (lignin:N ratio > 13). In all systems, excess-asynchrony of available N was pronounced during vegetative stages and at harvest, while insufficient-asynchrony occurred at reproductive stages. During potato cropping season at Thika, Org-High showed highest positive N fluxes (> 20 kg N ha⁻¹ day⁻¹) at planting and tuber bulking stage. At early stages of maize and vegetables Org-Low and Org-High experienced up to 5 times larger negative N fluxes (insufficiency) compared to conventional treatments at Chuka site. The study recommends reducing N applications at planting and increasing N dosages at reproductive stages of crops.