Interference between rows and between plants within rows of a wheat crop, and its effects on growth and yield of differently-spaced rows.
A seed drill with 2 adjacent spouts blocked was used to sow winter wheat so that there were rows (a) 18 cm apart, (b) 18 cm from the next row on one side and 53 cm on the other, (c) 53 cm apart. Throughout the growth period (b) continued to take up more N than (a), produced more shoots and ears per plant and per m of row and had more leaf area. The greater leaf-area duration in (b) was the main cause of the larger dry weight per m of row at ear emergence and of the higher straw yield, and accounted almost entirely for the larger grain yield. NAR before ear emergence was slightly greater in (b) than (a), but differences in grain: leaf ratio were not significant. Widely spaced rows (c) absorbed more N per m of row than (b) but had no more shoots or ears per m of row. Leaf area was slightly less in (c) than in (b) before ear emergence but was greater afterwards. The higher straw yield in (c) was entirely due to higher NAR, but the higher grain yield was due to greater leaf-area duration and slightly higher grain: leaf ratio. Results indicated that closely-spaced rows competed mainly for nutrients and that competition for light was important only at wide spacing. Stems were thicker and stronger at wide spacing. Irregularities in spacing of the drill and in the flow of seed had effects on growth that persisted until harvest, but yield per unit area of crop was not appreciably affected. RB.