[Moisture and nutrient characteristics of deep layer soil in apple orchards on the Luochuan highland of Shaanxi, Northwest China].

Taking the 11-, 15-, 20-, and 43 years old apple orchards on the Luochuan highland of Shaanxi, Northwest China as test objects, this paper measured the moisture content in 0-1500 cm soil layer and the organic matter and total and available nitrogen, phosphorous, and potassium contents in 0-300 cm soil layer, with the soil moisture and nutrient regimes as well as their variation characteristics with apple tree age and soil depth analyzed. The moisture content in 0-1500 cm soil layer in 11-, 15-, 20-, and 43 years old apple orchards was averagely 18.6%, 13.7%, 17.0%, 11.5%, and 13.1%, respectively, and decreased with apple tree age. Soil desiccation did not occurr in the orchards with supplementary irrigation, but a slight or medium soil desiccation occurred in the rainfed orchards. Nevertheless, the moisture content in 0-300 cm soil layer in the rainfed orchards was still higher than that in wheat field. The contents of organic matter and total and available nitrogen in 0-300 cm soil layer in the five apple orchards were less than 10 g.kg-1, 0.75 g. kg-1, and 50 mg.kg-1, respectively, all at shortage level, whilst the content of available phosphorous in 0-300 cm soil layer was 3.30-6.42 mg.kg-1, being moderate in upper soil layer and scarce in deep soil layer. The content of available potassium in 0-300 cm soil layer was 78.09-98.31 mg.kg-1, presenting abundant. The contents of nutrients were all higher in 0-100 cm soil layer than in 100-300 cm soil layer. The soil organic matter and total and available nitrogen contents and the soil nutrient index (SNI) all presented a trend of decrease after an initial increase with the increasing apple tree age. The contents of the test nutrients except total potassium in 0-100 cm soil layer all decreased rapidly with soil depth, while those in deeper soil layers kept relatively stable. There existed significant correlations between the contents of soil organic matter, total nitrogen, available nitrogen, total phosphorous, available phosphorous, and available potassium, but no significant correlations between the contents of soil total potassium and other nutrient factors.