Tillage, Rotation Sequence, and Cultivar Influences on Brown Stem Rot and Soybean Yield

Yield of soybean [Glycine max (L.) Merr.) is often reduced when grown in fields using no-till (NT) and shorter crop rotations with corn (Zea mays L.) than with conventional tillage (CT) and longer crop rotations. The objective of this study was to determine the effect of tillage system, rotation sequence, and cultivar on severity of brown stem rot (BSR) [caused by Phialophora gregata (Allington and D.W. Chamberlain) W. Gams] and yield of soybean. Field studies were conducted near Arlington, WI, for 4 yr (1989–1992) on a Piano silt loam (fine-silty, mixed, mesic Typic Argiudoll) under both NT and CT. Seven crop sequences with soybean were evaluated: (1) first-year soybean after a minimum of 5 yr corn; (ii) soybean annually alternated with corn; (iii) 2, 3, 4, 5 yr of continuous soybean after 5 yr of corn; and (iv) continuous soybean. When averaged over all rotations, severity of BSR was 38% greater and yield of soybean 10% less in NT than in CT. Severity of BSR was 30% greater and yield 15% lower in annually alternated soybean grown in NT than in CT. First-year soybean following 5 yr of corn had 44% less severity of BSR, 11% greater yield, and 4.8% greater seed weight than soybean annually alternated with corn. Severity of BSR tended to increase, and yield and seed weight of soybean tended to decrease with an increase in frequency of soybean in the rotation. Severity of BSR was almost 10 times greater, yield 19% less, and seed weight 10% lower in BSR-susceptible cv. Corsoy 79 than in the BSR-resistant cv. BSR 101 across all tillages and rotations. The reduction of soybean yield observed with NT and shorter crop rotations was attributed primarily to greater severity of BSR. Research QuestionThe importance of reduced tillage systems has increased due to concerns of soil erosion and field-work time requirements. No research has determined the effect of reduced tillage systems or the interaction of tillage systems with crop rotation on the severity of brown stem rot (BSR) of soybean. Our study was conducted to determine the influence of tillage and crop rotation sequence on the severity of BSR and yield of soybean. The effects of BSR on soybean production were measured by comparing disease severity ratings and yield of a BSR-susceptible cultivar to a BSR-resistant cultivar. Literature SummaryPhialophora gregata, causal fungus. of BSR, is believed to survive only in colonized soybean residue between soybean crops. Increasing importance of BSR as a disease of soybean in Iowa has been attributed to increases in soybean acreage and fewer years of nonhost crops between soybean crops. Disease severity of BSR was lower, and yield was 13% higher in soybean grown in rotation culture than in continuously cropped soybean. Yield of soybean was lower with a BSR-susceptible cultivar of soybean than with a BSR-resistant cultivar as less tillage was used and as years between soybean crops were reduced. Study DescriptionThis study was conducted for 4 yr on Plano silt loam at Arlington, WI. Treatments: Tillage systems (2) CT (moldboard plow) and NT Crop rotation sequence (7) First-year soybean after a minimum of five consecutive years of corn Soybean annually alternated with corn 2, 3, 4, 5 yr of continuous soybean following 5 yr of corn Continuous soybean N rate (2) 0 and 30 lb UAN/acre Soybean cultivars (2) ‘Corsoy 79’ (BSR-susceptible) and ‘BSR 101’ (BSR-resistant) Applied QuestionsWhat is the effect of NT on severity of BSR and yield of soybean? Severity of BSR in BSR-susceptible Corsoy 79 was 40% greater (Fig. 1) and yield was 16% less (Fig. 2) in NT than in CT when averaged across all rotation sequences. The severity of BSR in BSR 101 was reduced 90% compared with Corsoy 79 and did not differ between NT and CT (Fig. 1). The yield of BSR 101 was 5% less in NT than in CT, and was 24% higher than Corsoy 79 across both tillages (Fig. 2). Seed weight of soybean in NT was less than in CT and lodging of soybean was greater in NT than in CT. Is there an explanation for the greater severity of BSR in NT than in CT? Other research found P. gregaia to survive only in colonized soybean residue between soybean crops. Thus, the inoculum of P. gregata could be greater in NT than in CT. Decomposition of crop residue is slower in NT than in CT. How does NT interact with crop rotations on severity of BSR? The severity of BSR in Corsoy 79 was more than 100% greater in NT and 70% greater in CT in annually alternated soybean than the severity of BSR in first-year soybean following 5 yr of corn (Fig. 1). Severity of BSR in Corsoy 79 was 30 to 60% greater in NT than in CT with annually alternated soybean and rotation sequences with more consecutive years of soybean. With annually alternated soybean, yield of Corsoy 79 was 20% lower in NT and 6% lower in CT than the yield of Corsoy 79 as grown as first-year soybean. Yields of Corsoy 79 in NT were 15 to 25% lower than in CT for rotation sequences after the first-year soybean. The reduced effectiveness of longer crop rotation in lowering the severity of BSR and increasing soybean yield with NT compared with CT demonstrates how cultural practices can interact negatively. Cultivars resistant to BSR can reduce the effect of this negative interaction. This research also emphasizes the importance of soybean cultivar selection when reduced tillage systems or shorter crop rotations are implemented in soybean production. Fig. 1Seventy of brown stem rot as influenced by rotation, tillage, and cultivar, averaged over two N rates and 4 yr. Years in rotation of soybean are: 1 = first-year soybean after 5 yr of corn; C/S = soybean alternated annually with corn; 2, 3, 4, 5 = second-, third-, fourth-, and fifth-year soybean, respectively; Cont. = seventh-, eighth-, ninth-, and 10th-year soybean in 1989,1990,1991, and 1992, respectively. An area under disease progress curve (AUDPC) was calculated to present the seventy and progress of foliar symptoms of BSR for each year. Vertical bar represents FLSD (0.10). Fig. 2Yield of soybean as influenced by rotation, tillage, and cultivar, averaged over two N rates and 4 yr. Years in rotation of soybean are: 1 = first-year soybean after 5 yr of corn; C/S = soybean alternated annually with corn; 2, 3, 4, 5 = second-, third-, fourth-, and fifth-year soybean, respectively; Cont. = seventh-, eighth-, ninth-, and 10th-year soybean in 1989, 1990, 1991, and 1992, respectively. Vertical bar represents FLSD (0.10).