土壤无限制水分区间的修正研究

土壤无限制水分区间(NLWR)是指土壤水势、通气状况和机械阻力对作物生长发育没有限制作用的土壤水分含量区间。在保持其上限即土壤田间持水量或通气孔隙为10%时的土壤含水量不变的基础上,该研究对下限进行了修正,取土壤总水势为-0.3 MPa时的含水量或土壤机械阻力为0.85 MPa时的含水量作为NLWR的下限,代替原有的是永久萎蔫点或土壤机械阻力为2.0 MPa时的含水量。用上限的最小值减去下限的最大值,即可计算出NLWR。与原有的NLWR或土壤最小限制水分区间相比,修正后的NLWR更具有现实意义。NLWR为0时所对应的土壤容重(D b)称为临界容重(D b-thr),可以作为田间土壤物理质量管理的判断标准。当D bD b-thr时,土壤物理性质对作物产生阻碍作用,需进行土壤改良;当D bD b-thr时,只要土壤含水量处于NLWR之内,土壤物理性质对作物生长无影响,此时NLWR可以作为农田水分灌溉管理的依据。

Modification of Non-limiting Water Range in Soil

The range in soil water content,which is bounded by the upper and lower soil water content over which water,oxygen,are not hmiting to plant growth,was defined as soil optimum water range.The upper limit （wet end） of NLWR is determined not only at water content at field capacity,but also the capability of providing adequate aeration for plant roots （usually taken as a minimum air filled porosity of 10％）.The lower limit （dry end） is not only limited to permanent wilting point but also the ability of root penetration which is measured as soil mechanical resistance （SMR） taken at an arbitrary value of 2.0 MPa.The lower limit of NLWR was replaced by the total soil water potential （ψtot） threshold point （soil water content at ψtot =-0.3 MPa） and the water content at SMR =0.85 MPa.The NLWR can be calculated by the minimum of the upper limit minus the maximum of the lower limit.The modification of NLWR is agree with its concept and soil management in field.The soil bulk density （Db） at NLWR =0 is defined as threshold bulk density （Db-thr）.The Db-thr is recommended as a soil physical quality index for soil management in field.If Db ＞ Db-thr,the plant growth will be inhibited by soil physical properties and soil amendment is required.When Db is lower than Db-thr,the NLWR is the best guidance and principle for irrigation in field.