Many new varieties of winter annual legumes are now available for pastures in Mediterranean type climates. Since little work has been reported comparing the relative responses of these legumes to fertilization, 10 varieties of subclover, 6 of rose clover, 3 annual Medicagos, and 2 other annual clovers were grown in the greenhouse on a soil known to be deficient in P and S. There were four levels of P with S applied. The nil and highest P levels were repeated without S. Yield differences between varieties and species were small where no P or S was applied. Responses to S alone were generally not significant, but responses to P only and P plus S varied significantly. Differences in response to P and S fertilization were as great among varieties of a given species as between species. Highest yielding clover varieties tended to have lowest percentages of P and S. Differences in P and S uptake by the clover varieties were significant; however, uptake responses to fertilization tended to be relatively smaller than yield response differences, indicating that some varieties utilized absorbed nutrients more efficiently than others. Response to fertilization apparently must be considered on a varietal basis rather than generalizing about species.

Phosphorus deficiencies are widespread in California annual grasslands and in other areas of the world where subclover (Trifolium subterraneum L.) is an important legume. Therefore, the effects of clipping frequency and stage of growth on critical levels of P in subclover were studied. Critical P level was defined as percent P in the clover part when lack of P limited clover yields to 95% of those obtained with adequate P. In pot experiments subclover was grown in P‐deficient soils fertilized with increasing amounts of P until no additional increase in yield was obtained. When leaves were sampled from plants 48 to 151 days of age, the critical level decreased from 0.61 to 0.11% P, but changes after 120 days were not statistically significant. At day 120, leaves from plants previously defoliated 0, 1, 2, or 3 times had critical values of 0.11, 0.18, 0.23, and 0.28% P, respectively. The last three determinations were for leaves of the same physiological age harvested 13 days after the previous clipping. At 120 days critical P values in stem tissue also increased with increasing frequency of defoliation.

No abstract

Sulfur deficiencies are widespread in areas of California annual grassland where bur clover (Medicago hispida) is an important legume. The growth of this species is greatly increased by applications of S where S is deficient. The purpose of this study was to obtain information useful in assessing the sulfur status of annual grasslands in which bur clover occurred. The clover was grown in nutrient solution with varying levels of available S. Total S and SO4‐S concentrations in immature and mature leaves and in middle and lower stems were studied in relation to dry matter production. The concentration of total S where yields were 95% of maximum (“critical concentrations”) was 0.225% for both immature and mature leaf blades and was 0.080% for middle and lower stems. The “critical concentrations” for SO4−S were 160, 140, 100, and 160 ppm for immature and mature leaves and middle and lower stems, respectively. Organic S (total S minus SO4−S) reached a maximum at about 0.250% in leaves and about 0.100% in the stems. Where S was applied in luxury amounts unmetabolized sulfur accumulated as SO4−S. Highest concentrations were found in the lower stems, lesser amounts in the upper stems, and least SO4−S was found in the leaves.