Effects of straw incorporation on nitrogen absorption of split fertilizer applications and on rice growth
A greenhouse experiment investigated the effect and mechanism of straw incorporation (0 and 6 t ha−1) on the absorption of fertilizer nitrogen (N) of split applications and on the growth of rice shoots and roots. N fertilizer was split into: (1) base fertilizer (BF), incorporated before transplanting; (2) tillering fertilizer (TF), broadcasted at tillering stage; and (3) panicle-formation fertilizer (PF), broadcasted at panicle-formation stage. 15N-urea was used as one of three splits. To evaluate the hypothesis that straw incorporation influences the 15N absorption of one split by enhancing 15N immobilization or changing root growth, we measured the 15N residual rate in soil at maturity and root growth throughout the rice-growing season. Straw incorporation significantly decreased 15N absorption of BF, accompanied by significantly higher 15N immobilization in soil than in the no-straw treatment. However, straw incorporation significantly increased 15N absorption of top-dressing (both TF and PF), accompanied by significantly greater dry matter and length of surface roots (0–5 cm depth) throughout the rice-growing season (top-dressing 15N was seldom found in soils > 5 cm). Shoot dry matter with straw incorporation decreased significantly in the early stage but increased in the late stage, compared with the no-straw treatment, and shoot total N with straw incorporation decreased significantly throughout the rice-growing season (this negative effect had decreased by the late stage). To better synchronize N supply with rice demand and reduce the risk of water eutrophication, N levels of BF and top-dressing should be reviewed when straw is incorporated.