PARTITIONING OF SPRINKLER IRRIGATION WATER BY A CORN CANOPY

The total sprinkler irrigation amount is partitioned by the crop canopy into three major components:stemflow, throughfall, and interception storage. A study of the partitioning process by a fully developed corn canopyunder low wind conditions was conducted. Nearly 3000 measurements of stemflow were made over the course of23 irrigation/precipitation events using 240 different plants during the two years of the study. At the same time, nearly300 measurements of the throughfall were made. The objectives were to determine if the process varies between sprinklertypes, to determine what factors affect the partitioning process, and to develop models for the process. The partitioningprocess was examined at three plant spacings and six irrigation amounts under high-pressure impact sprinklers (HI), lowpressurespray heads on drop tubes at a 2.2 m height (LS), low-pressure spray heads at a 4.1 m height (LS-4.1), and alsounder natural precipitation. Stemflow decreased linearly with plant spacing and increased linearly with irrigationamount. Throughfall increased linearly with both plant spacing and irrigation amount. After tasseling, stemflow is thepredominate flow path for sprinkler irrigation water, accounting for 53% at a typical plant spacing of 20 cm. Throughfallaccounted for 43% of a typical irrigation amount (25 mm). Interception storage, estimated by algebraic closure, was 1.8mm when averaged over all events. Comparisons of the developed models with previous research indicates reasonablestability of the partitioning process even though corn production systems and corn plant structure have changed overtime. Statistically significant differences occurred in the partitioning process between the LS, LS-4.1 and the HI systems,with the LS-4.1 and HI systems being more similar to natural precipitation. The similarities in stemflow between theLS-4.1 and the HI systems suggests that the differences in stemflow for the LS system may be caused by the height andangle at which applied water intercepts the crop canopy. The average stemflow percentages for the three plant spacingswas 46, 43, and 43% for the LS, LS-4.1, and HI systems, respectively.

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