生物炭施用对稻田氮磷肥流失的影响

针对宁夏引黄灌区稻田过量施肥导致土壤养分利用效率低的问题,通过田间小区试验,在优化施氮条件下(240kg·hm~(-2)),设4个生物炭水平(0、4500、9000、13500kg·hm~(-2)),研究施用外源生物炭对稻田氮磷流失和土壤养分含量的影响。结果表明:生物炭对稻田田面水氮素动态产生影响,表现为田面水中全氮、硝态氮含量随生物炭用量的增加而降低,铵态氮表现则相反;全氮和铵态氮的最大峰值出现在第1次追施氮肥后的第2天,最大值为34.86、8.28mg·L~(-1);硝态氮最大峰值3.31mg·L~(-1)出现在第2次追施氮肥后的第2天。随后均迅速下降,全氮含量在施氮肥后10d回到第1次追氮前的含量水平,并趋于稳定,铵态氮和硝态氮则在7d后。生物炭对田面水全磷未产生显著影响,全磷含量在第1次施氮肥后3d达到峰值,为3.69mg·L~(-1),之后迅速下降,6~7d后降至追氮前的含量水平,并趋于稳定。生物炭处理显著降低了稻田全氮流失量8.03%~13.36%,高量炭处理(13500kg·hm~(-2))显著提高了土壤全氮和有机质含量,提高幅度分别为41.2%和27.5%(P0.05)。说明生物炭对稻田磷流失、土壤全磷和速效磷含量无显著影响,对降低稻田氮素淋失表现出积极效果。

Effects of Biochar Application on the Losses of Nitrogen and Phosphorus in Surface Water of Paddy Field

Applied high rates of nitrogen (N) fertilizer in rice production may result in lower N use efficiency in a paddy rice field of the Yellow River irrigation region, Ningxia. To reduce N and phosphorus (P) leaching and improve fertilizer use efficiency are important for sustainable and water quality. Thus, a field plot experiment was conducted to study the effect of exogenous biochar application on the loss risk of N and P and soil quality in a paddy field. Four biochar rates, i.e., 0, 4500, 9000, and 13500kg·ha-1 with optimum nitrogen rate (240kg·ha-1) were chosen. From May to October 2014, we determined the contents of NH4+-N, NO3--N, total N (TN) and total P (TP) in the surface water of paddy field during the whole rice growth period. The results showed that biochar amendment decreased the contents of both TN and NO3--N but increased NH4+-N content in the surface water. The contents of TN and NH4+-N reached the peak on the following day of the first top dressing and the maximum values were 34.86 and 8.28mg·L-1 respectively. The content of NO3--N reached the peak on the following day of the second top dressing and the maximum value was 3.31mg·L-1. Then TN leveled off after 10 days, but the NH4+-N and NO3--N contents approached a relatively stable level after a week. There was no significant difference in TP content in the surface water between the biochar addition and the control treatments. The content of TP peaked 3 days after fertilization and decreased rapidly afterwards, then leveled off after another 6-7 days. On the other hand, biochar amendment decreased TN leaching by 8.03%-13.36% relative to control, but the high-level biochar amendments (13500kg·ha-1) significantly (P<0.05) increased the contents of TN and soil organic matter by 41.2% and 27.5% respectively compared with the control. There was no significant difference in TP and available P contents in soil between the biochar addition treatments and the control. Our study has revealed that biochar could positively reduce N leaching in the rice fields, while there has no significant effect on P loss.