不同矿化度微咸水灌溉冬小麦对下季作物产量和周年土壤盐分平衡的影响

Annual soil salt balance and crop performance under brackish water irrigation during the winter wheat season

冬小麦夏玉米一年两熟是环渤海低平原主要粮食作物种植模式,该区淡水资源匮乏,但浅层微咸水相对丰富,在降水较少的冬小麦生长季,适当利用微咸水代替淡水灌溉对维持冬小麦稳产高产有重要作用。冬小麦季实施微咸水灌溉后土壤盐分累积如何影响下季作物夏玉米生长以及对土壤周年盐分平衡影响,是微咸水能否长期安全利用的关键。为探究上述问题,于2015—2019年连续4年在环渤海低平原中国科学院南皮生态农业试验站进行冬小麦季不同矿化度微咸水灌溉定点试验,共设置含盐量为1 g·L^(-1)淡水(F)、3 g·L^(-1)微咸水(S3)、4 g·L^(-1)微咸水(S4)、5 g·L^(-1)微咸水(S5)4个梯度,在拔节期灌水1次,灌水量均为70 mm;另以生育期不灌水作为对照(旱作,CK)。结果表明,不同矿化度微咸水灌溉处理间冬小麦产量没有显著差异,但平均比CK显著增产31.6%。同时,冬小麦生长季微咸水灌溉均增加了收获时1 m以上土层的含盐量,并随灌溉水含盐量增加而增加;对1 m以下土层含盐量影响不明显。夏玉米播种时灌溉70 mm淡水不仅解决了土壤墒情不足问题,并可使0~20 cm土层盐分控制在1 g·kg~(-1)以下,保证夏玉米出苗和群体建立,对夏玉米产量没有显著影响。经过夏季降雨的淋洗,S3、S4和S5处理0~40cm土层含盐量降低幅度超过30%,深层土壤含盐量变化不明显,1m以上土层可以实现周年盐分平衡。本研究表明冬小麦-夏玉米一年两季种植,冬小麦耐盐能力较强的特征使其生育期可以通过不大于5g·L^(-1)的微咸水灌溉维持稳产,在保证夏玉米出苗水进行灌溉的条件下,夏玉米季通过雨季降水淋盐维持0~1m主要根层土壤不发生明显积盐过程,可实现长期微咸水灌溉下土壤和作物安全。

The annual double cropping system of winter wheat-summer maize is a stable cropping system in the low plain of the Bohai Sea.Owing to the shortage of fresh water and the relative abundance of shallow saline water in this region,saline water is used to irrigate winter wheat.The accumulated salt in the soil after the winter wheat season affects the following summer maize season,and the annual soil salt balance is affected by saline irrigation.To address these issues,a continuous 4-year field study was conducted at the Nanpi Eco-agriculture Experimental Station of Chinese Academy of Sciences from 2015 to 2019.Four treatments were set up to irrigate winter wheat once using irrigation water(70 mm)with different total salt contents at the jointing stage,i.e.,freshwater 1 g·L^(-1)(F),3 g·L^(-1) brackish water(S3),4 g·L^(-1) brackish water(S4),and 5 g·L^(-1) brackish water(S5).There was also a treatment without irrigation(rain-fed,CK).The results showed that there was no significant difference in winter wheat yield among the four irrigation treatments,and the average yield with irrigation was 31.6%greater than that of CK.Irrigation using brackish water increased the soil salt content of the top 1 m soil profile during winter wheat harvesting.The soil salt content increase was proportional to the salt content of irrigation water.There were no significant differences in the soil salt contents below 1 m.The necessary irrigation using 70 mm freshwater for the seedling establishment of summer maize after winter wheat harvest reduced the salt content of the top 20 cm soil layer,which created favorable soil conditions for maize growth.No significant differences in summer maize yield were observed among different treatments.With concentrated rainfall during the summer monsoon season,the salt content in the top soil layer(0–40 cm)for the S3,S4,and S5 treatments decreased by more than 30%due to leaching,but the salt content of deep soil did not change.The results showed that the high salt tolerance of winter wheat maintained a stable yield with saline water irrigation.With irrigation at maize sowing and the subsequent summer rainfall,the accumulated salt is leached out of the major root zone to enable the continued use of saline water irrigation for winter wheat in this region.