GROWTH OF SHOOTS AND ROOTS, AND INTERCEPTION OF RADIATION BY WHEAT AND LUPIN CROPS ON A SHALLOW, DUPLEX SOIL IN RESPONSE TO TIME OF SOWING

Crops of lupin (Lupinus angustifolius us L. cv. Gungurru) and wheat (T riticum aestivum cv. Kulin or Spear) sown close to the break of the se ason and 3-6 weeks later were grown on a duplex soil at East Beverley, WA, over 3 seasons. The overall aim of the work was to examine the in fluence of time of sowing on growth and water use of the crops, and th is paper reports their growth and yield.Early sowing resulted in great er shoot weight of all crops (up to 2.8 t/ha for lupin and 1.7 t/ha fo r wheat at maturity) and grain yield of lupin, but grain yield of whea t was increased in only 1 of the 3 seasons. The principal effect of th e delayed sowing was to reduce the duration of linear growth; the rate of the initial exponential phase was slightly reduced by later servin g as was the rate of growth during the linear phase in lupin (by about 1.5 g/m(2) . day) but not in wheat. Late sowing generally reduced bot h the number of pods/ears per unit area and the number of grains per p od/ear. Doubling the density of sowing in one of the seasons had no ef fects on the shoot weight and grain yield of lupin with early or late sowing but decreased those of wheat. Downward root growth of early-sow n crops averaged 5.2 mm/day for lupin and 8.7 mm/day for wheat in the 3 seasons and ceased at about 0.8 m; time of sowing had no effect on t hese measures. Root weight at flowering was greater in lupin than in w heat crops, and root weight of lupin was about 0.5 of total plant weig ht during vegetative growth compared with 0.25-0.3 in wheat. Typically , only 5-6% of the root length of both crop species was present in the clay layer at flowering irrespective of sowing time. The proportion o f radiation intercepted reached a higher maximum value for early-sown crops (about 0.75 in 1991 and 0.90 in 1992) than late-sown crops (abou t 0.60 in 1991 and 0.8 in 1999). The conversion coefficients of radiat ion to dry matter were very similar (about 1.8 g/MJ) for both species, but the greater partitioning of dry matter to roots in lupin than whe at meant that conversion coefficients for shoot dry matter were greate r in wheat (1.43-1.68 g/MJ) than in lupin (0.93-1.16 g/MJ). The result s demonstrate that early sowing produced larger crops of both lupin an d wheat; this resulted in larger lupin yields, but yield of wheat was affected by disease and drought during grain filling.