| The effects of drought stress (R1 to R7) and insect defoliation (R2 to R4) on soybean physiology, growth, and yield were examined in a two-year study. Plots were protected from natural rainfall by a rainout shelter that remained away from the plots during dry conditions. Artificial defoliation was used to closely model injury caused by discrete populations of lepidopterous larvae. Both vegetative growth and seed yield were reduced by drought stress, while the effects of defoliation primarily were limited to reductions in yield components. Compensatory regrowth (leaf emergence) was observed in defoliated plants. This regrowth, however, did not significantly affect leaf area. Loss of latent leaf area potential in young, expanding leaves may result in an underestimation of the impact of defoliation on canopy size. Senescence of lower leaves was delayed and photosynthetic rates of remaining, intact leaves were greater in defoliated plants, as has been found in previous studies. The response of leaf photosynthesis to defoliation was similar in drought-stressed and well-irrigated plots.;Leaf area removed did not predict yield as well as did remaining leaf area, especially when data were pooled over irrigation rate. However, data expressed as remaining leaf area has limited pest management applications unless these data can be coupled with additional information, such as initial canopy size, pest population density, or predictions of future injury. No statistical interactions were found between irrigation and defoliation rates.;Recovery from drought stress beginning at R5 resulted in significantly greater weight per seed, while recovery starting at R6 did not affect yield components relative to plots stressed until R7. This is the first study to experimentally examine the recovery potential of stressed and unstressed, defoliated plants. |
