Vertical Distribution in Soil of Sprinkler-applied Phosphorus
Soil-immobile plant nutrients, such as P, accumulate near the soil surface in conservation cropping systems where tillage leaves crop residues on or near the soil surface and limits soil mixing. The objective was to determine, in field and laboratory experiments, the vertical distribution in soil of P applied in sprinkler irrigation water. Following P applications, distribution was determined from depth increment (1 or 2 cm) sampling on a Warden silt loam (coarse-silty, mixed, mesic, Xerollic Camborthids) and a Quincy sand (mixed, mesic, Xeric Torripsamments). The fertilizer materials applied in 10-mm irrigations were: monoammonium phosphate (227 g P kg−1), urea phosphate (192 g P kg−1), commercial white phosphoric acid (238 g P kg−1), and ammonium polyphosphate (149 g P kg−1) containing 61 g P kg−1 as polyphosphate. Application rates ranged from 50 to 400 kg P ha−1. Movement of P was about the same for all P fertilizer materials except ammonium polyphosphate, from which P moved only 60 to 70% of the depth of the other materials. Postapplication irrigation totals up to 160 mm at 10 mm d 1, which was applied without drying cycles, distributed P more uniformly with depth. The overall mean depths of P penetration across all treatments were 10.4 cm (SD = 4.04 cm) on the Quincy sand and 7.3 cm (SD = 4.93 cm) on the Warden silt loam. These depths of penetration and vertical distribution of sprinkler-applied P are probably sufficient to supply the P needs of crop plants under sprinkler irrigation.
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