Combined Effects of Soil Water Regimes and Rice Straw Incorporation into the Soil on 15N, P, K Uptake, Rice Yield and Selected Soil Properties

Understanding the effects of water regimes on nutrient uptake of rice plants, especially by different organic fertilizers is critical to improve long-term rice productivity. In a greenhouse experiment, the effects of soil water management and incorporation of rice straw into the soil on nutrient uptake, soil properties and rice productivity were studied in a clay soil. The treatment included two levels of soil water regimes (continuous submergence and alternate submergence-drying) and four rice straw levels (0, 5, 10 and 15 t ha-1). Results showed that, soil pH decreased slightly with increasing rate of rice straw application in both continuous submergence and alternate submergence-drying. Soil Eh values were correlated to rice straw application levels. Alternate submergence-drying in rice plant for some period of time significantly increased rice growth parameters and rice yield. Nitrogen in rice plant was derived mostly from fertilizer (higher Ndff) values in continuous submergence and alternative submergence-drying. The highest 15N atom% values in plant were observed at panicle initiation stage under both water regimes. Most of 15N uptake by rice plant was from the soil (averaged 53%). The uptake of P, K and Zn nutrients was greater in continuous submergence than in alternate submergence-drying.