Interactions

Abstract

Vegetable yields vary markedly from site to site even with crops grown on fertile soils and which receive plenty of fertilizer. Yield differences between two similar neighbouring soils were shown to be caused by differences in potassium uptake in the very early stages of growth. In another experiment on a range of 13 soils at one site, there were up to three‐fold differences in early lettuce growth attributable to differences in phosphate availability between the soils. In both sets of experiments, the recommended levels of broadcast fertilizer were used, but the seedlings were unable to exploit the fertilizer quickly enough to prevent nutrient stress. Indeed, a survey of the nutrient concentrations in lettuce seedlings sampled from commercial crops two weeks after sowing showed that phosphorus stress was common, even though the soils had relatively high levels of residual phosphorus and received generous amounts of broadcast fertilizer. Experiments show that the problems can be overcome by the use of starter fertilizers applied near the seeds at the time of sowing.

Key words:

• Nutrient stress
• potassium
• phosphorus
• seedling
• soil
• starter fertilizer
• variation
• yield