Growth and yield sensitivity of four vegetable crops to soil compaction

A 3-year field study conducted on an Eel silt loam soil (Aquic Udifluvent) compared cabbage (Brassica oleracea L. capitata group), cucumber (Cucumis sativus L.), snap bean (Phaseolus vulgaris L.), and sweet corn (Zea mays L.) for their growth and yield response to an artificially compacted soil layer beginning at about the 10-cm depth. Slower growing cabbage seedlings in compacted plots were more subject to flea beetle damage than the uncompacted controls. Prolonged flooding after heavy rainfall events in compacted areas had a more adverse effect on cabbage and snap bean than on cucumber or sweet corn. Sweet corn showed almost no growth reduction in one of the three years (1993) when relatively high fertilizer rates were applied and leaf nitrogen deficiencies in compacted plots were prevented. Maturity of cabbage, snap bean, and cucumber was delayed, and the average reduction in total marketable yield in (direct-seeded) compacted plots was 73%, 49%, 41%, and 34% for cabbage, snap bean, cucumber and sweet corn, respectively. Yield reduction in transplanted cabbage (evaluated in 1993 only) was 29%. In a controlled environment greenhouse experiment using the same soil type and similar compaction treatment as the field study, compaction caused a reduction in total biomass production of 30% and 14% in snap bean and cabbage, respectively, while cucumber and sweet corn showed no significant response. The growth reductions of snap bean and cabbage in the greenhouse could not be attributed to compaction effects on soil water status, leaf turgor, nutrient deficiency, or net CO2 assimilation rate of individual leaves. Root growth of sweet corn was least restricted by the compacted soil layer. The contrast between our field and greenhouse results indicates that the magnitude of yield response to compaction in the field was often associated with species sensitivity to secondary effects of compaction, such as prolonged flooding after rainfall events, reduced nutrient availability or uptake, and prolonged or more severe pest pressure.