Soil management effects on the nonlimiting water range

Abstract

Water, oxygen, temperature, and mechanical resistance (MR) are soil physical properties that directly affect plant growth. In this research, the nonlimiting water range (NLWR), defined as the range of soil water content in which neither water, oxygen, nor MR is limiting for plant growth, was measured on soil samples from three field experiments. Undisturbed soil core samples were collected from an experimental field on Wasco silt loam (coarse-loamy, mixed, nonacid, thermic Typic Torriorthents) amended with dairy manure (25 and 50 ton/ha), sludge composting biosolids/green waste (25 and 50 ton/ha), and a control treatment from Shafter Field Experiment Station, Kern County. Similar samples were collected from a Reiff loam (coarse-loamy, mixed, nonacid, thermic Mollic Xerofluvents) and Yolo silt loam (fine-silty, mixed, nonacid, thermic Mollic Xerofluvents) treated with conventional 4-year rotation, conventional 2-year rotation, low-input, and organic farming systems in the Sustainable Agricultural Farming System (SAFS) in Davis, CA. The third set of samples were from a fine sandy soil (mixed, thermic, Typic Haplargid) irrigated with four saline waters with EC values of 0.5, 4.0, 8.0, and 12.0 dS m −1 in a pistachio orchard located at Paramount Farms, Kern County, CA. The core samples were used to determine saturated hydraulic conductivity and water retention at −1500 kPa (wilting point) and −10 kPa (field capacity) to calculate the available water content and the NLWR. Oxygen diffusion rates (ODRs) were measured on the soil cores after they were equilibrated to field capacity, and MR was measured using an automated mini-penetrometer after the soil was equilibrated to −1500 kPa. The results showed that organic amendments did not significantly change the ODR, MR, NLWR, and saturated hydraulic conductivity ( K s). Mean values of MR and ODR were not significantly different in the four agricultural systems either, but soil under organic farming system had a relatively narrow NLWR because less water was retained at field capacity, indicating that the soil surface under this farming system has more large pores. The mean K s was significantly higher in conventional 4- and 2-year rotations than in organic and low-input treatments. Increasing irrigation water salinity above 4 dS m −1 progressively decreased the saturated hydraulic conductivity but had relatively little effect on other physical properties. In general, the treatment variables had relatively little effect on the NLWR, ODR, MR, or K s of surface soils, except for a decrease in K s when irrigated with waters with more than 4 dS m −1.