Soil fertility levels as influenced by long-time differential fertilization practices

Yields and resultant soil fertility levels from a 30-year experiment on soils of the Crosby-Brookston Catena under livestock or manure and cash crop, or residue, systems of farming are reported. In the livestock system manure and fertilizers were applied in various rates and ratios. In the cash crop system the crop residues and sufficient fertilizers were returned to the soil to make the returns of plant nutrients comparable to those in the livestock, or manure, system. Corn yields were increased 11 bushels per acre for the 30-year average over untreated plots by returning crop residues alone. During the last 4 years of the experiment, the differences were much greater. For instance, the increase in corn on plots receiving only residues over the untreated plots where neither residues nor fertilizer were applied was 18 bushels. Under the residue system, potash was the limiting factor in corn and soybean production. Wheat yields showed good responses to phosphorus fertilization in both the manure and the residue systems. Yields of the hay and corn crops were much higher on the manure plots than on the residue plots. Net removals, or deficits, of nitrogen and potash (K2O) for the 30-year period exceeded 1,500 and 350 pounds, respectively, per acre on all plots. The net removals of nitrogen and potash were greater from the crop residue plots than from manure plots. The manure plots had the greater removals of phosphorus. Where only manure was applied, the phosphorus deficit was over 400 pounds per acre, and was exceeded only by plots that received no residues (untreated) or crop residues only. To a great extent, the more nearly complete the fertilizer treatment, the greater was the amount of nitrogen remaining in the soil. Total nitrogen was significantly higher on plots receiving manure, or manure and fertilizer, than on plots receiving residues instead of the manure. Six tons of lime per acre applied during the 30-year period were insufficient to bring up and maintain the soil pH at 6.5 under any of the treatments. Only the residue plot receiving phosphorus alone showed a positive balance or gain of added nutrient over nutrients removed. It showed a slight gain of phosphorus. This plot was the only one approaching a medium level of available phosphorus. None of the treatments maintained a meduim level of potassium. On the manured plots, the availability of potash and phosphorus seemed to be increased by the manure as indicated by a consistently greater availability than would be expected from the computed balances of nutrients applied and nutrients removed in the crops. In addition to the superior yields, the manured plots when compared similar treatments in the crop residue system showed a higher of available potash and total nitrogen than on similarly treated residue plots.