DIFFERENCES IN RESPONSE TO AVAILABLE PHOSPHORUS AMONG WHITE CLOVER CULTIVARS

The selection of agriculturally important plant germplasms more tolerant of low P may increase productivity on P deficient soils and reduce P fertilizer requirements. Differences in response to P availability among six cultivars of white clover (Trifolium repens L.) were investigated in a series of pot experiments using a sand-alumina culture technique and two low P soils, an acid Hapludult with 2.6 mg Bray-P kg-1 and a calcareous Calciaquoll with 6.9 mg NaHCO3-extractable P kg-1. Plants were grown in the greenhouse or growth chamber for up to 63 d in solution [P] of 0 to 82 muM. Plant characteristics measured included dry mass and P concentration of shoots, coarse roots, and fine roots; P distribution within the plant; and root traits of total length, root hair length and number per unit root surface area, and root tip number. There were significant differences in shoot dry mass and P accumulation response curves among cultivars; cultivar rankings were consistent in sand-alumina and in soils, but differed from other reports in the literature. We found significant cultivar-by-solution [ P] interactions when only low vs. high P availabilities were compared, but not when response curves were generated and compared. Differences in herbage yield and P accumulation were associated with larger root systems, but there was no evidence of greater efficiency of P uptake or utilization in these cultivars.