15N Tracer Analysis of Nitrogen Distribution and Break-even in Paddy Soil under Water and Biochar Management

Abstract:

In order to reveal the distribution of ammonium nitrogen and nitrate nitrogen in different soil layers and the distribution of soil nitrogen in plants under water and biochar management, the accumulation and distribution of NH+4N and NO-3N, fertilizer NH+415N and NO-315N in 0~60cm soil layers under different water and biochar management were studied by combining field plots with 15N tracer microarea, and the distribution of soil nitrogen in plants under different water and biochar management was calculated. The results showed that the accumulation of NH+4N in paddy soil was decreased with the increase of soil depth under dryshallowwet irrigation. The accumulation of NH+4N and NO-3N in 0~20cm soil layer was increased by applying appropriate amount of straw biochar, while the accumulation of NH+4N and NO-3N in 20~60cm soil layer was reduced. The accumulations of NH+4N, NO-3N and fertilizer NH+415N, NO-315N in 0~20cm soil layer of rice under the same straw biochar application level were higher than those of flooding irrigation. The accumulation of NO-315N in 20~40cm and 40~60cm soil layers of dryshallowwet model was significantly lower than that of conventional flooding (P<0.05) Totally 979%~1396% of the soil nitrogen accumulated in rice under dryshallowwet irrigation was distributed in plant leaves, 15.71%~20.03% was in plant stems and sheaths, and 66.00%~74.50% was in plant panicles. Considering the breakeven of soil nitrogen pool in cold and black soil area, the best water and biochar management model was dryshallowwet irrigation plus 12.5t/hm2 straw biochar.