Effect of fertilizer management on potassium dynamics and yield of rainfed lowland rice in Indonesia

Rainfed paddy fields have a significant role as a buffer for rice (Oryza sativa L.) availability in addition to irrigated paddy fields. However, the optimization of rainfed rice fields is constrained by low rice productivity caused by low soil fertility including K deficiency, especially in light textured soils. The objective of this study was to determine the effect of fertilizer management in light-textured rainfed rice fields on the K dynamic and lowland rice yields. The study was arranged with a randomized block design, six replicates, and five fertilizer treatments (control, NP, NPK, NP+composted straw, NPK+composted straw). The observed variables were grain yield, yield component, exchangeable K, and nonexchangeable K. The yield of rainfed rice plants significantly increased with fertilizer management. The direct seeded rice (DSR) yielded grains 1.23-1.65 t ha-1 higher than the transplanted rice (TPR). Plant K uptake significantly increased with fertilizer application, where NPK fertilizer increased K uptake by 88.6% (DSR) and 71.9% (TPR). Exchangeable and nonexchangeable K in soil were generally high at 40 and 60 d after germination, and decreased in harvest time. The nonexchangeable K was generally higher than exchangeable K at 20, 40, 60, and 100 d after germination. The application of straw compost not only significantly increased grain yield, but also effectively provided K for plants in the form of exchangeable K and K slowly available K, so it was effectively used as an alternative supply of K to replace K from inorganic fertilizers.