title: Relationship between leaf area index and yield in double-crop and full-season soybean systems.
abstract: Previous research indicates a correlation between leaf area index (LAI) and yield of full-season soybean [Glycine max (L.) Merrill], which is a single crop planted early in the season. Leaf area index values of at least 3.5-4.0 in the reproductive stages are required for maximum potential yield. It is unknown how yields of double-crop soybean, which is planted late into harvested small grain fields, respond to changes in leaf area index. We hypothesized that double-crop soybean would be more sensitive to defoliation than full-season soybean. This study used linear and linear plateau models to describe the yield response of full-season and double-crop soybean to reductions in leaf area index through manual defoliation, and evaluated the yield response of double-crop soybean to reductions in leaf area index through natural insect defoliation. From 15 manual defoliation experiments over 3 yr, significant linear decreases in yield occurred in both full-season and double-crop soybean when leaf area index values were below 3.5-4.0 by developmental stages R4 to R5, whereas yields usually reached a plateau at higher leaf area index levels. Average yield loss was 769 +/- 319 kg ha(-1) for each unit decrease in leaf area index below the plateau; average maximum yield was 3,484 +/- 735 kg ha(-1). From eight field experiments over 2 yr, insect defoliators had no effect on double-crop soybean yield; leaf area index levels were above 4.0 by the developmental stage when leaf area index estimates were taken (R3 to R6). Therefore, double-crop soybean that maintains leaf area index values above the 3.5-4.0 critical level by mid-reproductive developmental stages can tolerate defoliating pests.
authors.affiliation: Department of Entomology, Virginia Tech Tidewater Agricultural Research and Extension Center, Suffolk 23437, USA.
authors.forename: Sean
authors.initials: S
authors.lastname: Malone
authors.forename: D Ames
authors.initials: DA
authors.lastname: Herbert
authors.forename: David L
authors.initials: DL
authors.lastname: Holshouser
mesh_terms: D000818:Animals; D018556:Crops, Agricultural; D007313:Insecta; D018515:Plant Leaves; D012621:Seasons; D013025:Glycine max