A field experiment was conducted to determine recovery efficiencies for applied N, P, and K under a system of total removal of forage (Cynodon dactylon L. Pers. ‘Coastal’) over a 3‐year period. Ammonium nitrate, (NH2)2CO, and (NH4)2SO4 were each applied in split applications of 0, 280, 560, and 840 kg N/ha each season. Soil levels of total N, chemically extractable P, and K were monitored each season. Results show that N recovery percentages ranged in the following order: (NH4)2SO4>NH4NO3 > (NH2)2CO. Characteristic decreases in recoveries occurred with increasing N rates. Source effects on recovery efficiencies for P were as follows: NH4NO3 ⩾ (NH4)2SO4 > (NH2)2CO. Average P recovery percentages for NH4NO3 were 34, 46, and 52% for rates of 280, 560, and 840 kg N/ha, respectively. Plant recovery of applied K was greatest for (NH4)2SO4 and lowest for (NH2)2CO. Average values for (NH4)2SO4 were 108, 165, and 222% for the low, medium, and high rates of N, respectively. Ammonium sulfate gave greater accumulation of soil N with time than NH4NO3 or (NH2)2CO while chemically extractable soil P and K were highest for NH4NO3.
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Matocha et al. (1973) studied this question.