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Heterodera glycines continues to be the number one yield limiting factor in soybean [Glycine max (L.) Merr.] across the Midwest. Several genetic and agronomic practices are available to assist growers in maximizing yield in a H. glycines environment. The objectives of this research were to (i) measure yield response to rotation and tillage systems and evaluate whether presence of H. glycines and reaction of cultivars to H. glycines modified this response, and (ii) determine if H. glycines population dynamics were related to source of resistance to H. glycines, rotation, or tillage systems. Field research trials were conducted during 3 yr (2006–2008) near Arlington, WI and Ames, IA. Main plots were no-tillage and conventional tillage systems. Subplots consisted of 10 rotation sequences involving corn (Zea mays L.) and soybean. Sub-subplots were three sources of H. glycines resistance. Crop rotation and source of genetic resistance were the most important factors to consider in maximizing seed yield and managing H. glycines across locations, whereas tillage was the least valuable tool in H. glycines management. Extended rotations decreased H. glycines populations, however this benefit was overcome by first or second year soybean. Results also show that continued reliance on one source of genetic resistance can lead to reproduction of H. glycines, regardless of source. Our results suggest that an integrated approach to H. glycines management that considers rotation, tillage, knowledge of H. glycines (HG)-type, and source of genetic resistance is needed to maximize seed yield and decrease H. glycines populations.

Inoculants containing Bradyrhizobium japonicum are available for soybean [Glycine max (L.) Merr.] production but may not be necessary in fields where soybean previously has been produced. The objective of this study was to determine yield response and probability of an economic return from inoculants in fields with a recent history of soybean production. Fifty-one inoculant products were evaluated in experiments (n = 73) conducted in Indiana, Iowa, Minnesota, Nebraska, and Wisconsin between 2000 and 2008. Inoculant products were similar and did not produce a yield response relative to an untreated control different from zero (P > 0.05) at 63 environments. Probability for a break-even economic return at a soybean sale price of $0.33 kg–1 was 59% for Nebraska, 36% for Wisconsin, 25% for Minnesota, 25% for Indiana, and 4% for Iowa. Attaining a return on investment of 67 kg ha–1 (a 2:1 return) reduced success to 11, 2, 1, 7, and 0.2%, for the five states, respectively. Data from this range of environments and products indicate that application of an inoculant offers limited success for either a yield increase or improved economic return on soils where soybean has previously been grown in the upper Midwest.

No-tillage cropping systems may benefit from the addition of winter annual cover crops through decreased soil erosion, accumulation of biologically fixed N, or increased crop yield. The objectives of this research were to assess the amount of cover provided by winter annual legumes and oat (Avena sativa L.) to quantify the fertilizer N equivalent value of each cover crop system and the effect of cover crop and N rate on corn (Zea mays L.) and grain sorghum [Sorghum bicolor (L.) Moench] grain yield. Two experiments, one in corn and one in sorghum, were conducted in 1997, 1998, and 1999. In each experiment, the main-plot effect was cover crop treatment while the subplot effect was spring N rates of 0, 56, 112, and 168 kg ha(-1). The addition of oat to the legume cover crop treatments increased fall ground cover but decreased total spring dry matter yield. Maximum spring dry matter yield was greatest in the hairy vetch (Vicia villosa Roth)-alone treatment. Hairy vetch alone also produced the greatest mean fertilizer N equivalent value in the corn and sorghum experiments, 43.6 and 56.9 kg N ha(-1), respectfully. These values, however, were variable among years. Corn and sorghum grain yield were greatest in the Austrian winter pea (Pisum sativum L.) and hairy vetch full seeding rate treatments, 5.19 and 7.06 Mg ha(-1), respectfully. Our results indicate that winter annual cover crops provide several distinct benefits to no-tillage corn and sorghum production systems and that cover crops should be selected based on specific grower needs.

No-till production systems coupled with decreased use of soil residual herbicides has led to increased populations of winter annual weeds. Therefore, research was conducted to quantify the effect of henbit interference and crop stand loss on soft red winter wheat grain yield and grain volume weight. The main-plot effect consisted of weed-free versus weedy plots. The subplot effect was winter wheat stand loss treatments of 0, 20, 40, 60, 80, and 100%. Henbit interference did not affect test weight; however, test weight decreased as percentage of stand loss increased. Henbit did not reduce crop yield at 18 $\\text{plants}/{\\rm m}^{2}$; however, at 82 and 155 $\\text{plants}/{\\rm m}^{2}$, crop yield was reduced 13 and 38%, respectively, when averaged across all stand loss treatments. Yield estimates based on wheat tiller or spike density decreased linearly as crop stand loss increased. Our results indicated that henbit interference coupled with crop stand loss may significantly decrease crop yield and profitability of wheat production systems.

An experiment was conducted in growth chambers to determine the influence of cold temperature regimes, designed to simulate winter temperature conditions and spring recovery, on the interaction between purple deadnettle and soybean cyst nematode (SCN). The study was a factorial arrangement of treatments with five levels of temperature (20, 15, 10, 5, or 0 C), two levels of exposure time to the temperature (10 or 20 d), and two levels of recovery time at 20 C following exposure (0 or 20 d). In general, purple deadnettle shoot and root growth increased with temperature and time. The ability of purple deadnettle to recover from cold temperatures declined as the length of time that the plant was subjected to the cold temperature increased. SCN juveniles per gram of root at the conclusion of the temperature treatment declined as the temperature increased from 0 to 15 C, likely a result of continued purple deadnettle root growth and the inhibition of SCN hatch, growth, or development at those temperatures. SCN female, cyst, and egg production per gram of root generally increased with temperature and occurred under all temperature regimes. The results of this research indicate that, after hatching, SCN juveniles can survive a period of cold temperature inside the roots of a winter annual and continue development when transferred to warmer temperatures. Therefore, in a field environment, where fall or spring alone may not be sufficient for SCN to complete a reproductive cycle on a winter annual weed, the nematode may be able to reproduce by combining the fall and spring developmental periods.