Field study with rock phosphate and superphosphate 1952 to 1990 and dissolution of rock phosphate in silage leachate

In a long term fertility trial conducted in northern Illinois, agronomic and economic effectiveness of rock phosphate (RP) was compared with super phosphate (SP) on crops consisting of oats-alfalfa (hay)-corn-corn (rotation "A") and corn-soybean (rotation "B"). Phosphorus applications ranged from 0 to 80 pounds P$\sb2$O$\sb5$/a. Agronomically, rotation "B" responded better than rotation "A". Eighty pounds of SP P$\sb2$O$\sb5$/a gave the highest yield in both rotations. In rotation "A" alfalfa (hay) and oats produced the highest and lowest yields, respectively. Corn yields were more than twice as high as those for soybeans in rotation "B". Corn yields were increased by 800 pounds/a at different P treatments when corn was planted following alfalfa (hay) as compared to continuous corn. In rotation "B", corn yields were increased by 2500 pounds/a compared to corn yields in rotation "A". Treatments had significant effects on crop yields; a square-root-quadratic model gave the best fit for both rotations. Gross profit was found to be higher for rotation "B" than rotation "A". By comparing the net present value for 16 years 80 pounds RP P$\sb2$O$\sb5$/a gave the highest value ($1958/a) in rotation ``A'', whereas a combination of 20 pounds RP P$ sb2$O$ sb5$ and 40 pounds SP P$ sb2$O$ sb5$/a brought the highest value (\$2638/a) in rotation "B". The optimum economic doses at typical market price ratio ($P$ sb2$O$ sb5$/\$ crop) were found to be 60 and 35 pounds P$\sb2$O$\sb5$/a/year through SP and RP, respectively for corn and 30-35 pounds P$\sb2$O$\sb5$/a/year either through RP or SP for soybean. Soil available P and adsorbed P were found to be higher with SP than RP treatments and were related to amount of P applied. Increase in total P due to RP and SP treatments was accounted for by increase in different inorganic P fractions. Al-P was highly correlated with available P. There was a good agreement between total P obtained by soil test and P calculated as the difference between total P (initial soil total P plus Fertilizer P) and crop removal. Low moisture corn silage leachate effectively dissolved RP because of its high butyric content, but this results in poor quality.U of I OnlyRestricted to the U of I community indefinitely during batch ingest of legacy ETD