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Tuesday, June 28, 2016, 10:30am - 11:30am
Spatial variability in soil N supply as affected by bulk density and soil water in non-puddled soil
Setia Sari Girsang
Research Affiliate Scholar
Soil Science Group
Spatial variations in soil type, soil water, and topography could have even greater effects on optimal fertilizer management and rice productivity in non-puddled than puddled soils. Site-specific nutrient management is needed to reduce production costs and enable more environmentally friendly agriculture. The study area was located in Los Baños, Laguna, Philippines (14.15º N and 121.246º E) on non-puddled soil in the Experiment Station of the International Rice Research Institute (IRRI). The objectives were to (1) measure spatial variation in bulk density, soil water, indigenous N supply, rice response to N, and infiltration rate across 36 locations in a 3.3-hectare rice field with non-puddled soil; and (2) assess whether indigenous N supply — as determined from soil inorganic N and yield in minus N plots —, bulk density, soil water, and soil infiltration rate could serve as predictive indicators of plant accumulation of N, grain yield with N fertilization, and N fertilizer requirements. Among soil properties, bulk density and anaerobic N mineralization (ANM) were most related to indigenous N supply and grain yield with N fertilizer. Low bulk density and high ANM were associated with high grain yield, plant N, and N use efficiency (NUE). Lower water-filled pore space and volumetric water were associated with accumulation of soil nitrate-N. Saturated hydraulic conductivity was inversely related to ANM, grain yield, and plant N across a 3.3-hectare rice field with non-puddled soil. Based on rice response in rice to N and an assumed target agronomic efficiency for N fertilizer of 12 kg ha-1, the optimal fertilizer N requirement ranged from 81 to 290 kg ha-1 with a mean 174 kg N ha-1 across 36 locations. The response of rice to N and hence the estimated optimal fertilizer N requirement were not correlated with inorganic soil N, bulk density, or anaerobic N mineralization at the start of the season. The results cast doubts on the likelihood of developing a robust soil measure at the start of a season for predicting N fertilizer requirements across variable soils.
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