Abstract The total effect of legumes on subsequent crop yields may be divided into two categories: (i) the effect of the N that they supply, and (ii) the net effect of all other contributions. Knowing the size of these two effects, plus the N response of the subsequent crops, allows N fertilization to be optimized for decreased energy use and for reduced pollution potential. Because the size of the legume effects vary, a study was made to estimate them on a mesic, Typic Hapludalf soil at Lancaster, Wisconsin from 1967–1976. The crop species included alfalfa (A, Medicago sativa L.), corn (C, Zea mays L.), oats (O, Avena sativa L.), and soybeans [S, Glycine max (L.) Merr.] in five crop sequences: continuous C, CSCOA, CCCOA, CCOAA, and COAAA. Four N treatments: 0, 84, 168, and 336 kg/ha were applied only to C. Crop sequence phases were assigned to whole plots in a randomized, complete block design with the N treatments in subplots. There was a highly significant effect of years on all crops due to weather variation and crop variety changes. Soybeans and A did not respond to residual N. Alfalfa yields were the same in all rotations (7.6 ± 0.04 metric tons dry matter/ha/year). The mean 0 yield (Y, quintals/ha) response to residual N (kg/ha) was described by Y = Minimum C(18.4 + 0.0354N), 24.93. Both A and S increased yields of C following these legume crops. Most of the increase was due to their N contribution, which was estimated with a Mitscherlich‐Spillman N response model as 50, 66, 51, 25, 3, 84, 24, and 71 kg N/ha to CSCOA, CS C OA, C CCOA, C C COA, CC C OA, C COAA, C C OAA, and C OAAA, respectively. The increases in C yields above that due to the legume N were estimated as the difference between the predicted maximum rotational and continuous C yields, specifically: 11, 8, 9, 4, 4, 11, 6, and 11 quintals/ha (in the same order as above).
Abstract The growth rate and yield of plant parts of partridge pea were compared to those of Korean lespedeza on 5 soil types at 2 levels of phosphorus fertilization and at 4 levels of plant population. Partridge pea seemed to be able to tolerate lower soil phosphorus levels, adverse physical soil conditions, and extremely low and high plant populations with less adverse effect on yield. It was also able to respond more to added phosphorus on the soils with adverse physical conditions and low natural levels of available phosphorus. Korean lespedeza responded more to added phosphorus on the soil which naturally had good physical condition and was naturally fertile. Leaf area, per se, was not a factor.
