Nutrient Management Research for Paddy Rice in Guizhou

Most of the nutrient management studies on paddy rice in Guizhou Province in the past were focused on medium to high fertility soils and largely ignoring the rice grown in the low to medium fertility soils. In order to improve paddy rice yield and nutrient management practices, three field experiments were carried out to test the effects of different N, P and K rates on rice yield and the soil nutrient status in the growing season. The objective was to determine the optimal fertilizer rates for paddy rice in three types of poor-fertility soils. Field experiments consisted of 12 treatments including five rates of N (0, 90, 120, 150, and 180 kg N/ha), four rates of P (0, 45, 90, and 135 kg P₂O₅/ha) and four rates of K (0, 90, 135, and 180 kg K₂O/ha). Nitrogen was used as urea (46% N), P as SSP (12% P₂O₅) and K as KCl (60% K₂O). Nitrogen and K were split applied as basal application at seedling transplanting and at tillering stage with proportions of 40:60, while P fertilizer was applied only once at seedling transplanting.

The available N and P in the soil increased significantly with a rise in N and P application rates from tillering to jointing stages, but the treatment differences narrowed down gradually towards maturity. The available K in soil, however, was not remarkably affected by K fertilizer application rates. Rice yields increased significantly by 23.5% to 38% in the highly reduced paddy field, 16.7 to 36.9% in the paddy field with low soil temperatures, and 16.7% to 36.9% in the yellow earth paddy field under different treatment combinations. Preliminary results suggest that the optimal fertilizer recommendation for paddy rice is 90-45-135 kg of N-P₂O₅-K₂O/ha in the highly reduced paddy field, 150-90-90 kg N-P₂O₅-K₂O/ha for the paddy field with low soil temperatures, and 180-90-180 kg N-P₂O₅-K₂O/ha for the yellow earth paddy field. These recommendations can be used in regions with similar soil types and other natural conditions and will be fine-tuned with future field validation experiments.