The effects of seed rate and row spacing on light interception, dry matter accumulation and seed yield, in non-dwarf and dwarf genotypes of autumn-sown determinate white lupins (Lupinus albus) in north-west Europe

Abstract

Two non-dwarf and two dwarf, autumn-sown determinate genotypes of white lupin (Lupinus albus L.) were sown at three sites in north-west Europe in the crop years, 1995–96, 1996–97 and 1997–98. Fully factorial experimental designs were used to analyse all combinations of genotype, seed rate and row spacing. Canopy expansion, expressed as the percentage of Photosynthetically Active Radiation (PAR) intercepted, and above ground dry matter (DM) accumulation were measured at frequent intervals during the main growing season at Rothamsted in the UK and Lusignan in France. The data from Rothamsted were used to derive models for the two processes, which were compared to the data from Lusignan, France.Crops with more than 23 plants/m2, 25 main stem leaves per plant or 1400 leaves/m2 were able to intercept more than 80% of the incident PAR. There were small differences in canopy expansion between genotypes. The non-dwarf genotypes began expansion slightly earlier (100–150 °Cd or thermal time in °Cdays, base temperature = 3 °C) than the dwarf genotypes. Crops sown on rows wider than 40 cm apart or with low plant densities (less than 23 plants/m2) were also slower to expand the canopy and intercept the PAR.The maximum quantity of dry matter accumulated by a genotype in the season (476–1044 g/m2) was related by a conversion efficiency (e) to the cumulative quantity of PAR intercepted. Values of e were generally in the range 0·92–1·65 g DM/MJ PAR during the early part of the growing season, which was comparable with other work on temperate-zone grain legumes. The non-dwarf genotype Ludet achieved an unusually large value of e (3·13 g DM/MJ PAR) and accumulated 1355 g DM/m2 at Lusignan in 1998. Late season drought in 1995–96 at Rothamsted produced some low values of e (0·75 and 0·88 g DM/MJ PAR).The seed yield was not related to the quantity of dry matter accumulated as harvest index varied from 22·3% to 49·7%. Maximum seed yield (4·54 t/ha) was produced from a low plant density (15·9 plants/m2). Mutual shading, caused by any combination of high plant densities, large numbers of leaves per plant or sowing on wide rows (>40 cm; at high plant densities within the rows) appeared to limit seed yield potential.