宁夏引黄灌区秸秆还田对麦田土壤硝态氮淋失的影响

以宁夏引黄灌区为例,探索秸秆还田条件下冬小麦土壤硝态氮淋失规律。试验设置常规施肥(CK)、常规施肥条件下施用4500kg/hm2(T1,半量还田)和9000 kg/hm2(T2,全量还田)秸秆3个处理。利用树脂芯法吸附10、20、30、60cm和90cm土层的硝态氮流失量。结果表明:硝态氮(纯N)淋失量6.26—12.85 kg/hm2,是冬小麦施用化肥氮量的2.78%—5.71%。与对照CK相比,T1和T2在10cm土层减少0.09%和3.97%;20cm土层减少8.51%和9.81%;30cm土层减少2.25%和10.34%;60cm土层减少23.85%和13.08%;90cm土层减少27.65%和20.73%。10cm和20cm土层,处理与对照以及处理之间均未到显著性差异(P0.05);30cm处理,T1与CK以及T1与T2未达到显著性差异,但T2与CK达到显著性差异表明全量还田效果最好;60cm土层,处理与对照、以及处理之间均达到显著性差异;90cm土层,处理与对照之间达到显著性差异,处理之间未达到显著性差异。硝态氮淋失主要发生在冬小麦返青至灌浆期间,占全生育期淋失量的52.95%—67.79%。T1、T2冬小麦产量增产率分别为10.11%与11.51%。可见,稻秆还田能够减少灌区土壤硝态氮淋失量。

Effect of nitrate leaching of winter wheat field based on straw application in the Yellow River irrigation area of Ningxia

The Yellow River irrigation of Ningxia is an important irrigation area in North China, and is a region with severe nitrate leaching and water pollution. Water quality in many drainage ditches is classified as Inferior Category V, and the main pollutants are nitrate and ammonium. The concentration of ammonium is generally 20-30 mg/L and the maximum concentration can reach 70 mg/L; therefore, quality of downstream water can be markedly affected. The contribution of field total nitrogen and ammonia nitrogen are up to 61%-66% and 76%-81%, respectively. The concentration of nitrate is more than 10 mg/L in half of all shallow groundwater. The content of soil organic matter is low in this area, which ranges from 9.2 to 14.5 g/kg with an average level of 10.2 g/kg. This may cause nitrate to be easily lost from the soil. In order to control the leaching of soil nitrate nitrogen in the Yellow River irrigation area, we intended to restore soil organic matter through the straw-returning method. In a case study conducted in the Yellow River irrigation of the Ningxia area, the patterns of nitrate leaching were studied in soil using the rice straw-returning. The field experiment contained three treatments including tradition fertilization without rice straw (CK), tradition fertilization combined with rice straw of 4500 kg/hm²(T₁, half straw application), and traditional fertilization combined with rice straw of 9000 kg/hm²(T₂, total straw application). Nitrate nitrogen leaching loss in soil layers 10, 20, 30, 60, and 90 cm deep was measured by the resin core method. We found that nitrate leaching losses with and without treatments ranged from 6.26 to 12.85 kg/hm² (pure nitrogen), representing 2.78%-5.71% of fertilizer nitrogen. Compared to CK, the nitrate leaching loss at 10 cm depth in T₁ and T₂ had a 0.09% decrease and 3.97% decrease, respectively; at 20 cm depth, T₁ and T₂ decreased the loss by 8.51% and 9.81%; at 30 cm depth, the reduction of nitrate leaching loss reached to 2.25% (T₁) and 10.34% (T₂); at 60 cm depth. Such decreases were 23.85% (T₁) and 13.08% (T₂); at 90 cm depth, T₁ and T₂ further reduced 27.65% and 20.73% loss, respectively. T₁, T_2, and CK were not significantly different in nitrate leaching loss at 10 and 20 cm depth (P<0.05). Furthermore, there was no significant difference between T₁ and CK or between T₁ and T_2. However, T₂ led to significant improvement at 30 cm depth, indicating that total straw application was an effective way to prevent nitrate leaching loss in the irrigation area. Nitrate nitrogen leaching losses among T₁, T_2, and CK at 60 cm depth were significantly different. Both treatments showed significant alleviation for nitrate leaching loss compared with CK at 90 cm depth, although there was no significant difference between these two methods. The critical period of nitrate nitrogen leaching loss began from spring to the early filling stage, because nitrate nitrogen leaching loss during this time was 52.95%-67.79% of the total. The yield increase of winter wheat in T₁ and T₂ fields was 10.11% and 11.51%, respectively. Taken together, these data suggest that the rice straw returning method is effective at reducing the nitrate nitrogen leaching loss at deep soil layers in the Yellow River irrigation of Ningxia area.