Partitioning soil-water losses in different plant populations of dry-land corn

In situ volumetric soil-water contents were measured on 11 days at 0.20 m depth intervals to 1.0 m in a field experiment with four replicates of a dry-land corn hybrid (Pioneer 3140) at plant populations of 37, 49, and 62 thousand plants haÿ1. These measurements were used to estimate total soil-water losses in each of the 12 field plots for each of the 10 measurement intervals. The area of the largest leaf on 10 plants in each plot was measured at 86 days after planting, when all the leaves on the plants were fully developed. Daily green leaf area indexes (GLAI) were calculated from these measurements. Climatic data collected at the experimental site together with the results for GLAI were used to calculate water balances in order to partition the total soil moisture loss for each measurement interval into bare soil evaporation, crop transpiration, and drainage below the root zone. The observed total soil moisture losses between the days of measurement compared well with values from the water-balance calculations. As plant population increased, the time to full canopy cover increased. Therefore, higher fractions of the soil water were lost to bare soil evaporation and drainage over time as the plant population was lowered. At the same time, the fraction lost to crop transpiration decreased as the plant population was lowered. This compensatory effect under dryland conditions resulted in almost identical total water losses by the three plant populations during the growing period. The calculated partitioning of the soil-water losses served to explain the experimental observations that, under dry-land conditions, it would be unlikely that total soil-water losses would be influenced by different plant populations of corn. # 1999 Elsevier Science B.V. All rights reserved.