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, CSCOA, CCCOA, CCCOA, CCCOA, CCOAA, CCOAA, and COAAA, 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).

The mycorrhizal relationship has interested biologists since its discovery by F r a n k 5. Since that time much study has been devoted to its occurrence and effect upon the associated higher plant. Our understanding of the mycorrhizal relationship is relatively advanced in the case of the ectotrophic mycorrhizas. The status of knowledge about the effect of the endotrophic vesicular-arbuscular mycorrhizae which occur on most crop plants, as well as many trees is, on the other hand, much more restricted. This lack of information is largely accounted for by the difficulty of isolating the vesicular-arbuscular fungi in pure culture. Only B a r r e t t 2 has reported the successful isolation of vesicular-arbuscular fungi (probably Endogone spp.) and the synthesis of mycorrhizae with them. We have successfully repeated B a r r e t t ' s isolation, however, we have consistently failed to obtain infection with the isolates. Evidence by investigators using various types of non-pure inoculum indicates that plants benefit from infection by the associated vesicular-arbuscular endophyte. This beneficial effect is shown by increased growth and uptake of certain nutrients. The uptake of phosphorus seems to be especially increased.

A 2‐year field study was conducted to examine the effects of different sorghum (Sorghum bicolor L. Moench) plant heights on yield and yield components of both sorghum and soybeans (Glycine max L. Merr.) and to compare production of intercrop and monoculture cropping systems. In 1977, ‘Amsoy 71’ soybeans were planted with a short (1.2 m) and a tall (1.6 m) sorghum cultivar in alternate 0.38 m rows on a Drummer silty clay loam (Mollisol, fine‐silty, mixed, mesic Typic Haplaquoll). In 1978, two short (1.3 m) and two tall (1.6 m) sorghum cultivars were intercropped with four soybean cultivars in 0.4 and 0.8 m rows on a Coto clay (Oxisol, clayey, kaolinitic, isohyperthermic Tropeptic Haplorthox). Soybean yields with tall sorghum were 71 and 18% less than those with short sorghum for 1977 and 1978, respectively. These reductions were due to fewer pods/plant in both years, fewer seeds/pod in 1978, and decreased seed weight in 1977. Narrow rows increased soybean yields 50% with short sorghum and by 35% with tall sorghum in 1978. Intercrop tall sorghum yields were greater than short sorghum yields by 86% in 1977 and 74% in 1978. All yield components except plants/ha contributed to the increase in 1978. Intercrop soybean yields were 37 and 69% of monoculture yields in 1977 and 1978, respectively. Intercrop sorghum yields were 40 and 45% of monoculture yields in 1977 and 1978, respectively. Land equivalent ratios were not different in 1977, but in 1978 they were greater with tall sorghum than with short sorghum, 1.17 vs 1.10, and were greater in intercrop than in monoculture, 1.14 vs 1.00.

Synopsis Alfalfa was established successfully in corn by planting the alfalfa the same day as corn. High corn yields were obtained when a 20‐inch area over the corn row was kept weed free and the alfalfa between the rows was clipped. Sixty‐inch rows produced 92% and 80‐inch rows produced 80% as much corn grain as that produced in 40‐inch rows. Lespedeza and alfalfa were the easiest legumes to establish under summer seeding conditions.

No abstract