Development and structure of foliage in wheat stands of different density

Abstract

The effect of sowing density (21, 85, 340 and 3400 plants per 1 m on the leaf area index (LAI), vertical arrangement of developing foliage and dry matter production was investigated in stands of wheat (Triticum aestivum L. cv. Niva). 1. With increasing sowing density. a) The LAI increased and the highest LAI = 9.6 was obtained with 3400 plants. m-2. The largest development of foliage took place at ear emergence with 85, 340 and 3400 plants. rn-2, and in the flowering phase with 21 plants. m-2. b) The overal leaf area duration was reduced, with a difference of 11 days between the lowest and the highest density. c) The number of leaves formed per one stem increased from 5 to 8. 2. An increase in theLAI affected the vertical distribution of leaf area and resulted in increased differenoes in relative light intensity between the top and bottom layers of the leaf canopy. Differences inLAI were linked with differences in leaf area duration and in the relative proportions of leaves of different age in the total number of leaves per 12 3. a) Shoot dry matter production increased with increasing density; the maximum of 3811 g. m-2 was obtained with 3400 plants.M-2. b) The dependence of grain yield on sowing density had a parabolic character; the maximum yields of 47001 g. m-2 and 442.8 g m-2 were obtained with 340 and 85 plants. respectively. c) The optimum LAI for the formation of grain yield was 2.3 to 3.2. d) The crop growth rate (C) increased with increasing density; the highest mean recorded C = 594 g. m. week-1 corresponded to LAI = 9.6. 4. Thinning the stands of 3400, 340 and 85 plants. m-2 in the phases of the 3rd leaf (22 days after sowing) and of tillering (30 days after sowing) to the next lower density resulted in a reduced LA leaf and tiller number, crop growth rate, shoot dry matter production and grain yield as compared with both the initial and standard densities. The role of foliage with respect to both maximum dry mater production and maximum grain yield was defined by an optimum range of relations between the rate of foliage development, leaf area, vertical structure and distribution of light intensity within the stand operating as a self-controlling system.