滴灌柑桔园肥料撒施对土壤pH值的影响

pH值为8左右的紫色土柑桔园，每株桔树安装3个流量3L／h的滴头，滴头导流管出水口每年移动一次。2002-2004年，每年分9～11次在树冠滴水线下或距出水口40cm范围内撒施复合肥和尿素等2100～3968g，干旱时滴灌。肥料撒施导致滴头出水口附近土壤酸化，土壤pH值下降主要局限于以出水口为中心、半径40cm的范围内，深度可达80cm。距滴头出水口水平距离5cm处、深15～20cm的土壤，一年内pH值降幅达到1．1。随土壤离滴头出水口距离的增加，土壤pH值下降幅度逐步递减。在距出水口水平距离40cm处、深40～85cm的土壤，每年pH值降幅只有0．1～0．28，而距滴头出水口水平距离60cm以上的土壤范围，对其pH值影响甚微，仅浅土层的土壤pH值下降0．1左右。

Effects of Broadcast Application of Fertilizers on Soil pH in Citrus Orchard with Drip Irrigation System

Hamlin sweet orange( C.sinensis) trees on Carrizo citrange rootstock were planted in calcareous purple soil with pH values of about 8.0 in the fall of 2000, and each tree was set 3 drippers with a flow rate of 3 L/h each. At the beginning of each year, drip emitters were relocated outward to fit the expanded root system. From 2002 to 2004, each tree was yearly broadcast applied 2 100-3 968 g urea or complex fertilizers under the tree canopy or around the drip emitters in 9 to11 times. If dry, the soil was drip irrigated following broadcast application. Soil was sampled for pH test at different depth and various distances from the emitters in Nov. Results showed that, the pH of soil not more than 40 cm from the emitters decreased significantly, and the closer the emitter, the lower the soil pH. The annual decrease of pH was 1.1 units for soil at 15-20 cm depth and 5 cm from the emitters, and 0.1-0.28 units for soil at 40-85 cm depth and 40 cm from the emitters. The pH at 60 cm or farther from the emitters had little changes since only a slight decrease of 0.1 unit was detected in the top 20 cm of soil.