分根区交替灌溉和氮形态影响土壤硝态氮的迁移利用

采用模拟土柱利用15N标记于土层10~20 cm、40~50 cm的方法,并设置不同形态氮肥供应(铵态氮、硝态氮)、灌溉方式(常规灌溉CI、分根区交替灌溉APRI),研究APRI下土壤中不同层次硝态氮的去向以及不同形态氮肥的影响。结果发现,APRI节水34.31%而不显著影响产量(P0.05)。随着15N标记层次下降,番茄植株对15N吸收利用率以及番茄收获后15N在1 m土层内的残留量显著下降,损失率显著增加。CI对10~20 cm土层的15N淋洗作用强于40~50 cm土层,APRI对10~20 cm的15N淋洗作用相对CI减弱,而促进了40~50 cm土层中61.3%的15N向上层土壤迁移。APRI下15N的损失率显著降低,利用率没有大幅度下降。相对于铵态氮肥料,硝态氮供应由于促进了植株生长及对15N的吸收,造成番茄收获后1m土层内15N累积量减少,而损失率与相应铵态氮供应的处理没有显著差异。因此分根区交替灌溉能够减少土壤中硝态氮的淋洗,并能够促进下层土壤硝态氮向上迁移,减少损失,增加植物吸收利用的机会;不同形态氮肥通过影响植物生长而影响土壤中硝态氮的去向。

Effects of alternate partial root-zone irrigation and nitrogen forms on utilization and movement of nitrate in soil

Abstract: Numerous evidences show that alternate partial root-zone irrigation (APRI) could save large amounts of irrigation water without significant yield reduction. In addition, intensive studies indicated that APRI could reduce nitrate leaching and increase the chance of nitrogen being absorbed by plant. However, all these studies could not discriminate the fate of nitrate in different soil layers under APRI. The fate of residual nitrate in specific soil layers and its regulation by different forms of nitrogen fertilizers (nitrate- or ammonium-nitrogen fertilizer) under APRI were studied in this paper by means of soil column experiment with labeled nitrate-N (K15NO3) applied to 10-20 cm or 40-50 cm layers. The results showed that compared with conventional irrigation, APRI saved 34.31 percent of irrigation water without significant yield reduction. Nitrate-nitrogen fertilizer improved nitrogen absorption by tomato plants to an extent of 27.0 percent, thus increasing plant growth and tomato yield. The rate of 15N absorbed by plant decreased significantly as 15N was labeled to deeper soil layer. The absorption of 15N by plant decreased 33.1 percentage for conventional irrigation and 23.0 percentage for APRI when the 15N-labeled layer decreased from 10-20 cm to 40-50 cm. Nitrate nitrogen supply promoted absorption of residual nitrate in soil profile to an extent of 53.9 percent compared with ammonium nitrogen supply by promoting tomato root growth and biomass accumulation. The leaching of soil residual nitrate from 10-20cm layer was more intensive than from 40-50 cm layer during tomato growth. For the soil columns with 15N labeled to the 10-20cm layer, the remaining rate of 15N in the 10-20cm layer was 2.7 and 23.1 percentage, the 15N accumulation peak moved downward 30cm and 10cm, and 15N accumulated in the 0-100cm soil layer took account of 60.9 and 75.2 percent of total 15N amount introduced by K15NO3, with loss rate 17.0 and 5.17 percentage, respectively, for conventional irrigation and APRI. However, for the soil columns with 15N labeled to the 40-50cm layer, the remaining rate of 15N in the original labeled layer was 38.1 percentage, whereas under APRI, 15N accumulation peak moved upward 10cm with 61.3 percent of 15N moved to 0-40cm layer, leading to 15N accumulation in 0-100cm soil 24.2 percent more than the conventional irrigation and a large extent of reduction of 15N loss. Compared with ammonium nitrogen supply, nitrate fertilizer promoted plant growth and thus 15N uptake, leading to a lower 15N accumulation after plant harvest in the top 100cm soil. However, there was no significant difference in 15N loss between soil columns fertilized with ammonium nitrogen or nitrate nitrogen. These results suggested that APRI could reduce soil residual nitrate leaching, and promote residual nitrate in deeper soil move upward, thus increasing the chance of being utilized by plant. Different forms of nitrogen fertilizer affect the fate of residual nitrate in soil profile through affecting plant growth.