The sensitivity of shoot growth of corn to the least limiting water range of soils

The least limiting water range (LLWR), the range in soil water content within which limitations to plant growth associated with water potential, aeration and mechanical resistance to root penetration are minimal, has been proposed as an index of the structural quality of soils for crop growth. An hypothesis that is implicit in the proposed use of LLWR as an index of soil structural quality is that crop growth is negatively related to the proportion of the total number of measurements in which the water content falls outside the LLWR (p(out)) and therefore given a certain climate positively related to the magnitude of the LLWR. The objective of this investigation was to test the hypothesis that plant response, specifically shoot growth rate of corn (Zea mays L.), can be functionally related to p(out) and the LLWR of soils. The study was carried out on a farm with a side-by-side comparison of no-till and conventional-till. Thirty two paired sampling sites were located along the two transects. The LLWR and p(out) were calculated for the 0-20 cm depth in each sampling site. Shoot growth rate (SGR) was measured during a 17 and 16 day period in 1992 and 1993, respectively that corresponded to the 10-11 leaf stage. Although the variation in p(out) accounted for a larger percentage of the variation in SGR than did LLWR, the correlation between SGR and LLWR was high and justifies further studies to determine if crop yield can be related to LLWR under different soil and climatic conditions.