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 L. cv. Gungurru) and wheat (Triticum aestivum cv. Kulin or Spear) sown close to the break of the season 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 influence of time of sowing on growth and water use of the crops, and this paper reports their growth and yield. Early sowing resulted in greater shoot weight of all crops (up to 2.8 t/ha for lupin and 1.7 t/ha for wheat at maturity) and grain yield of lupin, but grain yield of wheat was increased in only 1 of the 3 seasons. The principal effect of the delayed sowing was to reduce the duration of linear growth; the rate of the initial exponential phase was slightly reduced by later sowing as was the rate of growth during the linear phase in lupin (by about 1.5 g/m2day) but not in wheat. Late sowing generally reduced both the number of pod/ears per unit area and the number of grains per pod/ear. Doubling the density of sowing in one of the seasons had no effects on the shoot weight and grain yield of lupin with early or late sowing but decreased those of wheat. Downward root growth of early-sown 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 these measures. Root weight at flowering was greater in lupin than in wheat crops, and root weight of lupin was about 0.5 of total plant weight 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 of 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 (about 0.60 in 1991 and 0.8 in 1992). The conversion coefficients of radiation 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 wheat meant that conversion coefficients for shoot dry matter were greater in wheat (1.43-1.68 g/MJ) than in lupin (0.93-1.16 g/MJ). The results demonstrate that early sowing produced larger crops of both lupin and wheat; this resulted in larger lupin yields, but yield of wheat was affected by disease and drought during grain filling.

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