Corn Response to Least Limiting Water Range (LLWR) at Two Compaction Levels in a Clay Loam Soil

Water, oxygen, temperature, and mechanical resistance are the soil physical factors that can directly influence plant growth. Under favorable temperature not only sufficient water is available for the plant at the last limiting water range (LLWR), but also the other two factors are not limiting for the root activity. In order to study the corn single cross (Zea mays L. (response to the soil water content with reference to LLWR, a greenhouse experiment was conducted. Topsoil with clay loam texture was passed through 4.76-mm sieve, and transferred into PVC cylinders (diameter 15.2 cm and height 50 cm). The soil columns were compacted to achieve two levels of bulk densities (1.25 and 1.6 g cm-3). With three soil moisture levels (the LLWR range, less than its lower limit and greater than its upper limit), two compactions and three replications, 18 soil columns were prepared. Three corn seeds were planted in each column. After seedling emergence and thinning them to one plant per PVC pot, soil water treatments were applied at 5-leaves growth stage. Plant traits including plant height, leaf area, leaf relative water content and stomatal conductance were measured. The difference in these traits between the three soil water levels were significant (p<0.01). Increase in bulk density decreased LLWR (v/v) from 18% at 1.25 g cm-3 to 6% at 1.6 g cm-3. Mean values comparisons of the plant traits at both bulk densities showed that the soil water range defined by LLWR led to the highest values of the traits. Therefore, the thresholds values corresponding to air-filled porosity of 10%, permanent wilting point of 1.5 MPa suction and mechanical resistance of 2 MPa (as defined in the LLWR concept) were verified for the corn growth in the examined soil.