Submitted to: Transactions of the ASAE
Publication Type: Peer reviewed journal
Publication Acceptance Date: 8/5/2002
Publication Date: 12/1/2002
Citation: SADLER, E.J., CAMP JR, C.R., EVANS, D.E., MILLEN, J.A. SPATIAL VARIATION OF CORN RESPONSE TO IRRIGATION. TRANSACTIONS OF THE AMERICAN SOCIETY OF AGRICULTURAL ENGINEERS. 2002. V. 45. P. 1869-1881. Interpretive Summary: Truly optimized management of irrigation systems is difficult to accomplish when contrasting soil types occur under a single irrigation system, because different soils hold different amounts of water. Thus, if a loam and a sand are both initially well-watered, the crop on the sand will suffer water stress sooner than the crop on the loam. The manager must decide whether to oirrigate then, which might waterlog the loam, or wait, which will continue to stress the crop on the sand. Soil-to-soil differences in rooting depth, infiltration, and runoff further complicate the choices. New technology now enables site-specific management of irrigation, but no information previously existed showing how to optimally manage the irrigation to account for different soils within single systems. The Site-Specific Center Pivot Irrigation Facility at Florence SC enabled research to provide these data for the first time. An experiment measuring site-specific corn yield response to irrigation showed significant variation in response both among and within soil map units, even when the soil was surveyed on a fine scale. In all three years, the yield curves for different soils often had different maximums and slopes, indicating that site-specific water management may hold potential for optimizing water use in irrigation. This could be determined using these data for profitability analysis of site-specific irrigation. At the very least, the differences were enough to require that they must be accounted for in design and management of conventional irrigation systems.
Technical Abstract: Lack of basic knowledge about spatially varying crop response to irrigation hinders optimal irrigation management and economic analysis for site-specific culture. The objectives of this research were to measure the mean response of corn to irrigation amounts on 12 soil map units and compare variation in the response within and among soil map units. This experiment was implemented from 1999 through 2001 with a center pivot irrigation machine that had been modified to enable site-specific irrigation on small plots within a representative, highly variable Coastal Plain field. Four irrigation treatments (0, 50%, 100%, and 150% of a base rate designed to hold soil water constant) and two N treatments (134 and 225 kg/ha - the recommended rainfed and irrigated rates) were imposed in 2x4 factorial randomized complete blocks on 8 soil map units, plus randomized incomplete blocks on 4 additional map units. Consistently significant main effects in the analysis of variance included the water treatment in both linear and quadratic forms, plus the variation within soil map units. Variation in yield among soil map units at any point on the response curves approximated 25% of the maximum yield in all three years. Variation in mean irrigation amounts to produce maximum yield in the 8 most common map units varied 26%, 29%, and 52% of the base rate amount. These data, the first such known, have implications in the design, management, and economic profitability of irrigation under spatially varying soils.