Nitrogen balance in a four-year grain rotation, 1881 to 1921
1931
White, J.W. | Holben, F.J.
In a 4-year grain rotation, on a fertile soil, the accumulations of nitrogen during the period of sod, brought about by non-symbiotic fixation, together with that supplied by the clover roots, is sufficient to meet the normal demands of the grain crops. This is true only when lime, phosphorus, and potassium are liberally supplied. Thus in 40 years the application of 1,440 pounds of nitrogen on plat 28 has resulted in a total increased yield of only 62 bushels of corn, 16 bushels of oats, 68 bushels of wheat, and 1,400 pounds of hay in excess of the PK treatment. This is true in spite of the fact that no lime was used during the 40-year period. The fact that nitrogen is not a serious limiting factor in such a rotation is further emphasized when it is realized that a total of 1,440 pounds of nitric nitrogen applied during the 10 rotations has caused total increased yields of only 12 bushels of corn, 3 bushels of oats, 27 bushels of wheat, and 70 pounds of hay in excess of an application of 480 pounds of nitrogen applied to plat 26. The results of a supplementary phosphate experiment suggest that heavier applications of superphosphate on the PK and PKN treatments would have brought about a somewhat higher level of crop yields which, in turn, would have resulted in a more economic utilization of the applied nitrogen. It is true, however, that the major limiting factor for crop production is that of moisture distribution during the growing season rather than the lack of plant food. Thus, in 1928, when ample rain fell during the summer months, plat 28 produced 82.7 bushels of corn compared to an average annual yield of 58.3 bushels.
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