THE EFFECTS OF SOIL COMPACTION ON NODULATION AND GROWTH OF COMMON BEAN (PHASEOLUS-VULGARIS L)

As part of an investigation of factors limiting nodulation in the field, cultivars of common bean were grown in a sandy loam soil that had been either deep tilled (DT) to reduce compaction or repeatedly rolled by a golf cart or by a tractor followed by a golf cart. In 1991 and 1992, the tractor-rolling treatment was replaced by a conventional tillage system. Nineteen cultivars were grown in 1990; 10, in 1991; and 4, in 1992. In general, soil compaction decreased plant growth and yield but had no adverse effect on numbers or weights of nodules per plant. In 1990, nodule numbers and weights were increased by compaction in the first sample, 35 d after planting. In a combined analysis of the four cultivars common to all 3 yr, nodule weight as a fraction of total plant weight was increased by compaction. Thus, compaction had a more severe effect on overall plant growth than on nodulation per se. Numbers and weights of nodules differed among the cultivars, but they all responded similarly to compaction. Cultivars yielded differently, depending on the degree of compaction (i.e., cultivar X compaction interaction), but, even so, the cultivar that had the highest yield in the DT plots also had the highest yield in the compacted plots. For most characteristics, the severity of the effects of compaction varied with the year, presumably in response to different weather conditions.