Managing Soil Nitrogen under Rain-Fed Lowland Rice Production Systems in the Forest Agroecological Zones in Ghana

Abstract

Rice is the second most important cereal in Ghana after maize. However, current production levels are about 47% of the country’s requirements resulting in huge annual imports of the crop. One major constraint to production has been low soil nutrients and poor nitrogen management. Nitrogen is not only a major nutrient but also most often the most limiting nutrient element in lowland ecologies. With the introduction of improved soil and water management (“sawah” system) for lowland rice production, a study was conducted to determine the optimum nitrogen rates required. A randomized complete block design arranged in a split plot consisting of five levels of nitrogen as main treatments and three improved rice varieties as sub-treatments was adopted. Results showed that the total number of tillers per m2 increased significantly with increasing levels of N as was total dry matter production. However, total number of panicles did not show the same relationship. Total biomass yield increased significantly and linearly with increasing levels of N. Paddy yield significantly increased from 1.7 t ha−1 (control) to a maximum of 9.4 t ha−1 (90 kg N ha−1) before declining to 5.8 t ha−1 (150 kg N ha−1) in the order 0 < 30 < 60 < 150 < 120 = 90 kg N ha−1, respectively. This result significantly and positively reflected on grain harvest index (GHI) in the order 0.27 < 0.38 < 0.46 < 0.47 < 0.57 < 0.68 for 0, 30, 60, 150, 120 and 90 kg N ha−1, respectively. Nitrogen at 90–120 kg ha−1 was therefore recommended. These rice varieties in addition to other improved ones will also perform well in other environments with similar biophysical characteristics across the country