太湖地区水稻土的物理特性与少免耕法的关系

本文从土壤物理特性和作物生长的关系探讨了耕作的要求.土壤水分能量特性可被机械扰动改变,这是导致土壤粘闭的重要原因.水稻土的含水量和有效水均以表土高,而下层低,含水量和容重成线性负相关(n=62,r=-0.909^**).土壤扰动可提高持水量,长年免耕在干旱年份可能会出现水分不足问题.土壤含水量、气容量和机械强度三者的变化相互联系.由三个因素决定的小麦生长最佳范围是在水分吸力0.02-0.5巴内,而田间持水量大于塑性限,所以秋季耕作必然导致土壤粘闭.免耕土壤的容重一般在1-1.25g/cm₃之间,是稻麦生长的较佳环境,所以水稻土本身存在适合稻麦免耕生产的条件.根据水稻和三麦分别52和23组次对比试验,水稻免耕增产19斤/亩,三麦49斤/亩,均达到极显著水平(p=0.01).平田地区连续三年免耕土壤不恶化,囊水型土壤第二年开始有变差趋势,但产量不减低.免耕有保护土壤结构的作用,但不利于结构发展.

PHYSICAL PROPERTIES OF PADDY SOILS IN RELATION TO MINIMUM AND ZERO-TILLAGE METHODES IN TAIHU LAKE REGION

The present paper deals with the requirements of paddy soils for tillage and through study on the relattonship oetween the pnysicai properties of soil and the growth of crops. Experiment results revealed the great effect of the soil mechanical disturbance on water potential, which indicated that it is a major factor resulting in soil puddling; moisture content and the capacity of effective moisture were higher in topsoil than in subsoil, which shower that soil puddling increases water retention. The linear negative correlation between moisture content and bulk density was statistically significant (n=62,r=-0.909^**). Thus long-term zero-tittage soils can suvolv insufficient water for crop erowth. The most favorable codition for wheat. growth on paddy soil was the soil moisture suction ranging from 0.02 to 0.5 bar. Because field capacity is higher than plastic limit, plowing and pulverizing the soil following rice inevitably leads to soil puddling. The best growth of rice appeared at the bulk densities ranging from 1 to 1.3 g/cm², which was similar to those after the flooding of the soil of zero-tillage following wheat. Therefore, zero-tillage is suitable for paddy soil under cropping system of rice and wheat. The grain yields of rice and wheat under zero-tillage were increased by 142.5 kg/ha and 367.51kg/ha, respectively as compared with traditional tillage, according to the results obtained from 52 experiments of rice and 23 experiments of wheat. The physical properties were not deteriorated in permeable paddy soils under zero-tillage for three years and in waterlogged paddy soil for two years.