It is generally assumed that infiltration of sprinkler irrigation and rainfall under potato is uniform. However we observed non‐uniform infiltration beneath the hills of sprinkler‐irrigated potatoes (Solanum tuberosum L, var. Russet Burbank) grown on Plainfield loamy sand (Typic Udipsamment; sandy, mixed, mesic). The objective of this field study was to determine the effects of foliage interception and hilling on non‐uniform infiltration, since concentrating water in local zones would increase deep drainage and nitrogen leaching. To do this we traced the rainfall and irrigation infiltration pattern with Rhodamine WT dye and collected the stemflow in stem collars. Throughfall of rainfall, the soil water content, and soil water tension also were measured.
From 20 to 46% of the irrigation and from 4 to 23% of the rainfall on the canopy flowed down the stems. Stemflow increased the soil water content around the stems and moved Rhodamine dye deep beneath the soil surface. Deep movement of dye beneath the furrows was caused by runoff from the hills and by leaf drip from the outer foliage.
The results obtained suggest that irrigation and fertilizer management could be improved by taking this non‐uniform infiltration pattern into account. Smaller irrigations should improve water use efficiency and minimize nitrate leaching. Further, evaluation of solute movement by soil sampling should consider the spatial variation introduced by the non‐uniform infiltration. Finally, predictive leaching models should account for non‐uniform infiltration.
The objectives of this study were: (1) to examine how foliar carbon isotope discrimination (Delta) and oxygen isotope composition (delta(18)O) are related to tree growth, ash mineral nutrient concentration and foliar nutrient concentration in 7-year-old clones of the F(1) hybrid between slash pine (Pinus elliottii Engelm.) and Caribbean pine (P. caribaea var. hondurensis Barr. et Golf.) in subtropical Australia; and (2) to evaluate the potential of using foliar Delta, ash mineral nutrient concentration and delta(18)O measurements for selecting F(1) hybrid pine clones with high water-use efficiency (WUE) and growth potential. There were significant differences in tree growth, foliar Delta, delta(18)O and ash mineral nutrient concentration among the eight clones tested. Significant negative linear relationships existed between tree growth and Delta, extrapolating to zero growth at Delta = 24-30 per thousand. There were strong genetic correlations (r = -0.83 to -0.96) between Delta and tree growth, particularly tree height. Significant non-genetic correlations (r = -0.62 to -0.80) existed between Delta and foliar K concentration. Foliar delta(18)O, ash mineral nutrient concentration and foliar nutrient concentration were unrelated to tree growth. In the F(1) hybrid pine clones, variation in tree WUE, as reflected by Delta, was largely attributed to a genetic effect on leaf photosynthetic capacity rather than on stomatal conductance, as reflected by foliar delta(18)O.
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