High-input management practices are often heavily marketed to producers to increase soybean [Glycine max (L) Merr.] yield in already high-yielding environments. Field research was conducted in three locations within 6 states (Arkansas, Iowa, Kentucky, Louisiana, Michigan, and Minnesota) in 2009 to determine the effect of seed treatment, inoculant, foliar fungicide, additional soil fertility beyond state recommendations, foliar fertilizer, increased population over state recommendations, and narrow row spacing on yield. The high-input system (combination of the management practices) yielded higher than standard-input system (University recommended management practices) in only 8 of the 18 locations. Narrow rows, in both the high and standard-input systems, only increased yield in 4 locations. Inoculant did not increase yield at any location. Foliar fertilizer application and seed treatment increased yield in one location each. The additional soil fertility and fungicide application increased yield in two locations each. The increased population increased yields in 3 of the 18 locations; while an additional fungicide application at R5 only increased yield in 1 location. Foliar fertilizers at rates above commercial use did not increase soybean yield in Kentucky in 2008 or 2009. High-input production practices were largely unsuccessful at increasing soybean yield in these studies.

Maximizing productivity and profitability are the primary reasons for double-cropping soybean with small grain in the Mid-Atlantic, USA. Reduced double-crop yield can be attributed to: delayed planting that results in a shortened growing season and less vegetative growth; later-maturing cultivars that terminate main stem growth after flowering and have less growth and nodes; less soil moisture and plant-available nutrients due to small grain uptake; greater air and soil temperatures during vegetative stages that reduce early-season growth; and more favorable conditions for disease development during pod and seed formation. Field experiments were conducted in 2012 and 2013 in eastern Virginia to 1) evaluate cultivar stem growth habit, seeding rate, seed-applied inoculant, starter nitrogen (N) applied at planting, and foliar fungicide on soybean vegetative growth, total N uptake (TNU), seed yield and quality, and yield components; 2) determine the effect of starter N rate, applied with and without inoculant, on soybean vegetative growth, TNU, seed yield and quality, and yield components; and 3) evaluate the response of maturity group (MG) IV and V soybean cultivars to foliar fungicide. Greater seeding rates, inoculant, N, and fungicide typically were not required together to increase yield. Although cultivar interacted with other factors, early-maturing indeterminate 95Y01 yielded more than late-maturing determinate 95Y20 at 4 of 6 locations. Seeding rate interacted with other factors, but the greater seeding rate increased MG IV yield at 1 of 6 locations and decreased MG V yield at 2 of 6 locations. Starter N increased seed yield by 6 kg ha-1 per kg N applied until yield plateaued at 16 kg N ha-1, which continued to 31 kg N ha-1. When N rate was increased greater than 31 kg N ha-1, yield decreased. Fungicide increased yield for MG IV and V cultivars at 4 of 6 and 3 of 6 locations, respectively and prevented yield loss via mid- to late-season disease control, delayed leaf drop, and greater seed size. Optimum fungicide timing depended on environment and disease development. These data assisted in understanding agronomic inputs' combined or individual effects on double-crop soybean growth, canopy, N uptake, seed yield, and yield components. / Ph. D.

Differences in pea (Pisum sativum L.) and chickpea (Cicer arietinum L.) microbial compatibility and/ or their associated farming practices may influence root fungi of the following crop and affect the yield. The main objective of this research was to explain the difference in durum wheat (Triticum turgidum L.) yield the year after pea and chickpea crops through changes in the functional diversity of wheat root fungi. The effect of fungicides used on chickpea on the root fungi of a following durum wheat crop was studied using plate culture and pyrosequencing. Pyrosequencing detected more Fusarium spp. in the roots of durum wheat after fungicide-treated chickpea than in non-fungicide treated chickpea. Plate culture revealed that the functional groups of fungi responded differently to fungicide use in the field but the effect on total community was non-significant. Highly virulent pathogens were not affected, but antagonists were suppressed. More fungal antagonists were detected after the chickpea CDC Luna than CDC Vanguard. Fungal species responded differently to the use of fungicides in vitro, but the aggregate inhibition effect on antagonists and highly virulent pathogens was similar. The effect of chickpea vs. pea previous crop and different chickpea termination times on root fungi of a following durum wheat crop was studied. The abundance of Fusarium spp. increased after cultivation of both cultivars of chickpea as compared to pea according to pyrosequencing and was negatively correlated with durum yield. Plate culture analysis revealed that fungal antagonists were more prevalent after pea than both cultivars of chickpea and chickpea CDC Vanguard increased the abundance of highly virulent pathogens. The abundance of highly virulent pathogens in durum wheat roots was negatively correlated to durum yield. Early termination of chickpea did not change the community of culturable fungi in the roots of a following durum crop. It is noteworthy that Fusarium redolens was identified for the first time in Saskatchewan and its pathogenicity was confirmed on durum wheat, pea and chickpea. The classical method of root disease diagnostics in cereals is based on the examination of the subcrown internode. I evaluated the method by comparing the fungal communities associated with different subterranean organs of durum wheat. The fungal community of the subcrown internode was different from that of roots and crown, suggesting cautious use of this method.