Spatial variability in soil supply and requirements on non-puddled soils

In this study, spatial variation in indigenous N supply, water content, infiltration rate, and aerobic mineralization-N were determined in non-puddled soil (UE site) during 2014/2015 dry season (DS). This study was laid out in a completely randomized design (CRD) with nine locations. Correlation analyses were done through Pearson Correlation. For interaction involving N levels, trend analysis was used. Indigenous N supply (INS) and rice response to N fertilizer in relation to soil properties were also assessed. The results showed that non-puddled soil has high indigenous nutrient supply (INS) variability ranging from 0.3 to 3.1 Mg/ha in 0N (CV=55.3%) and 1.6 to 5.4 Mg/ha in N treatment (CV=30.6%). The NUE obtained in N treatment is slightly low; 12 kg/kg for AE sub N, 38 kg/kg for PE sub N, 33% for RE sub N, 45 kg/kg for IE sub N, and 21 kg/kg for PFPN. Three categories of water-filled pore space (WFPS) include low stress (83% WFPS) when grain yield (INS) reach 2.16 Mg/ha, low exchangeable NO sub 3 sup -, Ksat, BD, but high ANM (1.53 mg N/kg, 62 mm/h, 1.09 g cm sup 3, and 2.17 mg N/kg, respectively), for medium (78% WFPS) where grain yield (1.12 mg/ha), medium exchangeable NO sub 3 sup -, BD, ANM but high Ksat (2.77 mg N/kg, 1.16 g cm sup 3, 1.64 mg N/kg, and 130 mm/h, respectively) and high (73% WFPS) which is grain yield (0.65 mg/ha), high exchangeable NO sub 3 sup -, BD, and Ksat but low ANM (3.55 mg N/kg, 1.25 g cm sup 3, 103 mm/h, and 1.59 mg N/kg, respectively). High solar radiation during flowering to harvest did not increase grain yield due to low soil water and nutrient availability. Therefore, nitrogen fertilizer use efficiency and rice yield across fields can be increased by adjusting N management for spatial variations in soil properties such as thickness variability, bulk density, water content, nitrogen management, and saturated hydraulic conductivity. Fertilizer recommendations were therefore generated based on WFPS; 135 kg/ha when stress level is low (83% WFPS), 147 kg/ha for medium (78% WFPS) and 195 kg/ha for high (73% WFPS).