Effects of soil temperature and phosphorus supply on growth and composition of Lupinus angustifolius L. and L. cosentinii Guss

Abstract

Two Lupinus species, L. angustifolius L. and L. cosentinii Guss., were grown in pots in the glasshouse on a virgin lateritic soil, with two soil temperatures attained by immersion in water-baths at 10 and 20°C, and four rates of superphosphate ranging from 0 to 1792 kg ha-l. Air temperatures were not controlled. Dry matter, and phosphorus and nitrogen concentrations, were measured separately for tops and roots after harvest at 7 weeks. In a second experiment, the rate of early radicle elongation was measured for the two species in complete nutrient solutions at 10 and 20°.Water-bath temperature markedly influenced the growth of both roots and tops, growth with 20° being approximately double that with 10° in both species. At both bath temperatures, responses to superphosphate closely paralleled those observed previously on the same soil in the field. There was a slight positive interaction between bath temperature and superphosphate rate, but in the main the effects of the two factors were independent and additive. The results did not support the suggestion that reduced growth with low root temperature may be due primarily to reduced phosphorus uptake. Nor did they indicate reductions in nodulation, nitrogen fixation, or translocation of either nitrogen or phosphorus from roots to tops as likely causes. It is suggested that temperature may have directly affected the growth and/or metabolism of the roots, influencing their production of growth substances, which in turn influenced processes controlling top growth.