水分调控对盐碱地土壤盐分与养分含量及分布的影响

为给新疆地区盐碱地开发利用提供合理的灌溉指导,该文研究了滴灌条件下内陆干旱区重度盐碱地水分调控对土壤盐分与养分的影响,2008-2010年连续3 a设置了滴头正下方20 cm处5个土壤基质势下限控制灌溉:-5 kPa(S1)、-10 kPa(S2)、-15 kPa(S3)、-20 kPa(S4)和-25 kPa(S5),每个处理重复3次,按随机区组布置,于2008年试验前和2008-2010年试验后采集土壤样品(0~5、5~10、10~20、20~30和30~40 cm),测定土壤盐分(电导率、钠吸附比)以及土壤养分(速效N、P、K,全N、全P,有机质)含量。结果表明:3 a试验结束后,各处理0~40 cm土层土壤电导率与钠吸附比均显著(p0.05)降低,其中-5 kPa(S1)处理土壤电导率降至5.3 dS/m,降低幅度最大,为89%;速效N、P、K,全N、全P以及有机质含量较试验前均有显著升高,升高幅度均在20%以上,且与土壤基质势下限成正比。各处理速效养分均在滴头周围形成累积区,且随与滴头距离的增加而减少,养分全量与有机质含量在土壤剖面垂直分布差异显著。各处理土壤C/N均较第1年播种前降低,且降低率(4.3%~13.5%)随土壤基质势下限的降低而升高。综合土壤盐分的淋洗效果以及土壤养分的改良程度,滴头正下方20 cm处土壤水基质势控制下限-5 kPa可以作为内陆干旱区前3 a盐碱地水分调控的指导灌溉制度。

Effects of water regulation methods on soil salt, nutrient content and its distribution in overlying saline wasteland

Abstract: Drip irrigation with its characteristic of applying water at low discharge rate and high frequency over a long period of time can maintain constant and high soil water contents in the root zone, and reduce salinity in soil water by leaching, particularly near the drip emitters. Recently, numerous studies have evaluated the use of different levels of soil matric potential (SMP) to trigger drip irrigation in arid and semiarid regions and have successfully reclaimed saline and saline-sodic soils. However, very few studies have explored soil nutrients during the reclamation process under drip irrigation and hence understanding of nutrients in saline-sodic soil under drip irrigation is limited. A three-year experiment was carried out to investigate the soil salt and nutrient variation in saline wasteland during reclamation under drip irrigation in inland and arid region. The experiment included five treatments in which the SMP thresholds at 20 cm depth were controlled at ?5, ?10, ?15, ?20 and ?25 kPa. The treatments were replicated three times in a completely randomized block design. The results showed that the soil electrical conductivity (ECe) and sodium adsorption ratio (SAR) in 0-40 cm layer decreased significantly after three years of reclamation and the soil in -5 kPa treatment had the highest decreasing rate. By the end of the third cropping season, the ECe for -5 and -10 kPa treatments had reduced from 47.0 to 5.3 and 8.1 dS/m, respectively, which were in the range of the threshold salinity of cotton. The changes in SAR with time were similar as those of ECe. After the third irrigation season, the SAR, relative to the initial level, decreased by 40%-75% for the five treatments. Comparing with the initial value, soil available N, P, K, total N, P, and organic matter had a significant (P<0.05) increase and the increase rates were proportionate to SMP thresholds. The soil available nutrient for each treatment had a trend to concentrate around drip emitter and decrease with increasing soil depth. The distributions of soil inorganic N and available P and K in the soil profile were mainly affected by the characteristics of drip irrigation, irrigation regime and fertilization mode. With the reclamation in both soil chemical and physical properties, there were dramatic increases in soil N, P and K contents by the end of three years of the experiment. Since cotton growth became more vigorous during reclamation, there was also a considerable increase in soil organic matter by the end of 2010, and the increase rates were proportional to SMP thresholds. The vertical distributions of soil total nutrient and organic matter for the five treatments differed greatly. The soil C/N rate for each treatment had reduced compared to the initial value and the average reducing rates were increased as the SMP thresholds were decreased. Considering the soil salt leaching efficiency and nutrient improvement, an SMP of ?5 kPa could be used to trigger irrigation for saline wasteland reclamation in the first three years in Northwest China.