Availability of rock and other phosphate fertilizers as influenced by lime and form of nitrogen fertilizer
1944
Volk, G.W.
Greenhouse experiments were conducted to determine the relative effect of various sources of nitrogen on the availability of the phosphorus in rock phosphate, waste pond phosphate, calcium metaphosphate, and superphosphate. The soils used were Cecil and Eutaw clays and Hartsells and Norfolk sandy loams. Various nitrogenous fertilizers were applied to unlimed and limed soils, and in other cases lime was mixed with the fertilizer before application to the soil. The results may be summarized as follows: 1. On unlimed and limed Cecil clay the use of ammonium sulfate or urea with rock and waste pond phosphate greatly increased the yield of sorghum and oats over that resulting from the use of sodium nitrate. When the lime was mixed with the fertilizer before application to the soil, these increases were not obtained. 2. Even though the yields of sorghum and oats were greatly increased by using acid-forming nitrogenous fertilizers with the more insoluble phosphates, the yields were still much lower than those obtained with superphosphate. 3. he use of ammonium sulfate or urea with the more insoluble phosphates increased the uptake of phosphorus and calcium by sorghum and oats grown on both unlimed and limed soils. 4. The Ca:P ratio in oats fertilized with ammonium sulfate or urea was about twice as high as the ratio in oats fertilized with sodium nitrate. Sodium nitrate decidedly reduced the total uptake of calcium by oats, but did not affect the uptake of phosphorus appreciably. 5. Superphosphate and calcium metaphosphate were the best phosphate fertilizers for oats and sorghum, fused rock phosphate was almost as good as the former two, and ordinary rock and waste pond phosphate were decidedly inferior.
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