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Effect of Alfalfa on the Nitrogen and Phosphorus Requirements of Crops¹

ABSTRACT

The effect of N and P fertilization on crop yields under irrigation was evaluated in a nonlegume rotation (barley, corn, potatoes), and in a legume rotation (barley, alfalfa, alfalfa, alfalfa, corn, potatoes), on Gardena loam at Upharn, N. Dak. In the nonlegume rotation all crops responded to N. Phosphorus alone decreased yields of corn forage. However, with adequate N, P increased yields of barley, corn and potatoes.

In the legume rotation, the major effect of alfalfa was to supply available N. Added N fertilizer increased the yields of all nonlegume crops, but P additions increased yields of all crops. Phosphorus was available to potatoes 5 years after it had been added on the barley crop.

Yields of barley and corn tended to be higher in the legume rotation than in the nonlegume rotation, regardless of the fertilizer treatment. At the highest N fertilizer rate, yields of potatoes were similar in the two rotations. Higher yields in the legume rotation resulted mainly from the available N contributed by the alfalfa, but other factors also appear to be involved. Alfalfa, grown only in the establishing year, contributed available N to the succeeding corn crop in an amount comparable to alfalfa grown for a longer time.

¹ Contribution from Soil and Water Conservation Research Division, ARS, USDA. Presented before Div. IV, Soil Science Society of America, at Chicago, Ill., Dec. 6, 1960.

² Soil Scientists, Northern Great Plains Field Station, Mandan, North Dakota. C. W. Carlson is presently at the Plant Industry Station, Beltsville, Md. H. R. Haise is presently at Fort Collins, Colo.

Received for publication June 7, 1962. Accepted for publication September 13, 1962.