Despite the large differences between winter wheat (Triticum aestivum L.) current and potential yields (i.e., yield gap, YG) in Kansas, limited research is available on individual agronomic practices, or their combination, economically increasing yield. Our objective was to quantify the contribution of individual and combined management practices to reduce the wheat YG. An incomplete factorial treatment structure established in a randomized complete block design was conducted to evaluate the effects of 14 treatments on yield, YG, protein concentration, and net returns. The variety 'Everest' was evaluated at three locations in 2016 and 2017. We individually added six treatments to a farmer practice control (FP) or removed from a water-limited yield control (Y w ), which received all treatments. Treatments were: additional N, S, Cl, increased plant population, foliar fungicide, and plant growth regulator. Under no-till which had low disease pressure, the Y w increased grain yield by 0.4 Mg ha -1 as compared with FP, mostly led by additional N, S, increased population, and fungicide (0.2-0.4 Mg ha -1 ). In conventional till which had high-disease pressure, the Y w increased grain yield by 1.2 Mg ha -1 as compared with the FP, and foliar fungicide increased grain yield by 1.4 Mg ha -1 . Foliar fungicide and increased plant population economically reduced the YG for conventional till and notill, respectively. Net return analysis indicated that intensifying wheat management might be justifiable when using low-cost fungicides and if protein premiums are expected. Our results suggest that an integrated pest management should be preferred over an Y w approach with prophylactic pesticide application.

There is limited information on agronomic practices affecting wheat (Triticum aestivum L.) yield in intensively managed dryland systems despite the opportunity to narrow the existing yield gap (YG). We used a unique database of 100 intensively managed field‐years entered in the Kansas Wheat Yield Contest during the 2010 to 2017 harvest seasons to (i) quantify the YG, (ii) describe wheat management, and (iii) identify management opportunities and weather patterns associated with yield. We simulated wheat water‐limited yield (Yw) using Simple Simulation Modeling–Wheat (SSM‐Wheat) model for each field‐year to estimate YG as the difference between Yw and actual yield (Ya) and used 11 statistical approaches to test the association of management practices and weather variables with Ya. Wheat Ya averaged 5.5 Mg ha−1, and simulated Yw averaged 6.4 Mg ha−1, resulting in a YG of 0.9 Mg ha−1 (15% of Yw). High‐yielding fields had lower maximum and minimum temperatures and greater cumulative solar radiation and precipitation during grain fill. Varieties susceptible to fungal diseases responded to foliar fungicide (0.8–1.4 Mg ha−1), whereas resistant varieties did not. Seeding rate was negatively associated with Ya, as yield quantile 0.99 was 7.5 Mg ha−1 and decreased by 2.7 Mg ha−1 for every 100‐seed m−2 increase in seeding rate above 305 seeds m−2. In‐furrow P fertilizer, previous crop, tillage practice, and N timing were also associated with Ya. We conclude that fields entered in yield contests have closed the exploitable YG, and there are opportunities to improve Ya through improved management in regions with stagnant wheat yield.

Tillage system and P fertilizer placement can aff ect plant root growth and therefore water and nutrient uptake. Th e objective of this study was to evaluate the eff ect of P fertilizer placement and tillage system on soybean [Glycine max (L.)] root growth and grain yield under induced drought stress. A fi eld study was performed at two locations in southern Brazil, during the 2014/2015 season. Phosphorus fertilizer placement and tillage combinations were evaluated using triple superphosphate at 31 kg P ha-1. Treatments included: (i) strip-tillage with deep band (ST-DB); (ii) strip-tillage with band-applied 5 by 5 cm (ST-B); (iii) no-till with broadcast (NT-BR); (iv) no-till with band-applied 5 by 5 cm (NT-B); and (v) no-till with surfaceband (NT-SB). Root length density (RLD) and root diameter were evaluated at 0-to 25-cm depth in 5-cm intervals. Yield was evaluated under rainfed as well as under induced drought conditions. Th e ST-DB treatment showed increased total RLD among treatments, with about 58% greater RLD than the NT-BR treatment, and 46% greater RLD than the NT-B treatment at the 15-to 25-cm soil depth. Furthermore, the soybean yield penalty with the ST-DB treatment was lower than any other treatment with a yield reduction of about 9 and 0.3% at respective locations under induced drought stress. Results from our study showed that the ST-DB treatment contributed to enhance soybean root growth at deeper soil layers and improved overall resilience to induced drought.

Intercropping 568A gronomy J our n al • Volu me 102 , I s sue 2 • 2 010 ABSTRACT Nitrogen fertilizer is an important input for corn (Zea mays L.) production and leaching losses contribute to NO 3 -N in water systems. Th is study was conducted to determine whether a kura clover (Trifolium ambiguum M. Bieb.) intercropped corn system could reduce corn N fertilization need and NO 3 -N in the soil profi le, while maintaining corn productivity. Two systems were studied at six sites in Iowa, soybean [Glycine max (L.) Merr.]-corn intercropped with established kura clover and soybean-corn without kura clover. Six N fertilizer rates were applied to corn in each system. Excessive kura clover competition caused reduced corn population, delayed development, and reduced grain yield in 2006. More vigorous kura clover growth suppression in 2007 resulted in similar yield between the kura clover and no-kura clover systems, with greater yield in the intercropped kura clover at a site with coarse-textured soil. Th e kura clover system did not reduce corn N fertilization requirement, as measured by response in plant N stress and grain yield. Th e kura clover also did not infl uence NO 3 -N in the soil profi le before, during, or aft er the growing season. Th ese results diff er from other studies where kura clover intercropping has reduced corn N fertilization need and not reduced corn yield. Intercropping corn with kura clover posed the challenge of suffi ciently suppressing the clover to allow successful corn establishment and production, and in addition did not provide potential benefi ts such as reduced N fertilization requirement or less NO 3 -N in the soil profi le.

Plant breeding has increased the yield of winter wheat (Triticum aestivum L.) over decades, and the rate of genetic gain has been faster under high fertility in some countries. However, this response is not universal, and limited information exists on the physiological traits underlying the interaction between varieties and fertilization. Thus, our objectives were to identify the key shifts in crop phenotype in response to selection for yield and quality, and to determine whether historical and modern winter wheat varieties respond differently to in-furrow fertilizer. Factorial field experiments combined eight winter wheat varieties released between 1920 and 2016, and two fertilizer practices [control versus 112 kg ha -1 in-furrow 12 -40-0-10-1 (N-P-K-S-Zn)] in four Kansas environments. Grain yield and grain N-removal increased nonlinearly with year of release, with greater increases between 1966 and 2000. In-furrow fertilizer increased yield by~300 kg ha -1 with no variety × fertility interaction. Grain protein concentration related negatively to yield, and the residuals of this relationship were unrelated to year of release. Yield increase was associated with changes in thermal time to critical growth stages, as modern varieties had shorter vegetative period and longer grain filling period. Yield gains also derived from more kernels m -2 resultant from more kernels head -1 . Historical varieties were taller, had thinner stems, and allocated more biomass to the stem than semidwarf varieties. Yield gains resulted from increases in harvest index and not in biomass accumulation at grain filling and maturity, as shoot biomass was similar among varieties. The allometric exponent (i.e., the slope between log of organ biomass and log of shoot biomass) for grain increased with, and for leaves was unrelated to, year of release. The ability of modern varieties to allocate more biomass to the kernels coupled to an early maturity increased grain yield and grain N-removal over time. However, increases in grain yield were greater than increases in grain N-removal, reducing grain protein concentration in modern varieties.

Five research teams identifi ed parallel obstacles when concurrently attempting to conduct meta-analyses on the air and water quality impacts of on-farm 4R nutrient management practices. Across projects, system complexity and the lack of relevant data from cultivated and grassland agriculture fi eld trials impeded the application of standard meta-analytical procedures. Because challenges were comparable across projects, the 4R Research Fund technical leadership tasked the researchers with recommending improvements in fi eld research design, data collection, and reporting to enhance future agri-environmental data syntheses and meta-analyses. Here we outline statistical and analytical issues unique to meta-analysis and data synthesis in agriculture, discuss critical data and reporting gaps in the existing literature, and provide specifi c recommendations for researchers, funders, and journals. Key obstacles developed when fi eld studies did not include complete descriptive or response data (per treatment and experiment year), measurement uncertainty, estimation error in treatment eff ects, or simultaneously measured nutrient losses and crop yield. Others did not report crop nutrient uptake or their apparent recovery effi ciencies. To alleviate such challenges for subsequent research, we make the following recommendations: (i) use common meta-data protocols for consistent units and terminology; (ii) clearly defi ne treatments and controls; (iii) provide complete, tabular, full-factorial response data for each year and location; (iv) collect and report a minimum set of auxiliary data; and (v) establish requirements for data curation and repositories in funding and publication cycles. Implementing these in future nutrient management research will facilitate more robust meta-analyses and other data synthesis eff orts.A.J. Eagle, Environmental Defense Fund,

Appropriate poultry manure management is essential to ensure maximum crop N utilization and reduce risk of negative environmental impact. Th is study was conducted to evaluate the eff ect of three application times (late fall, winter, and spring preplant) on N availability from two sources of poultry manure [chicken (Gallus domesticus) and turkey (Melleagris gallopavo)] for corn (Zea mays L.) production. Manure was applied based on total N, intending to supply 84 and 168 kg total N ha -1 . Urea fertilizer was applied at the same time as the manure at six rates (0, 34, 67, 100, 134, 168 kg N ha -1 ). Soil classifi cation used for the study was primarily Clarion (fi ne-loamy, mixed, superactive, mesic Typic Hapludolls) and Nicollet (fi ne-loamy, mixed, superactive, mesic Aquic Hapludolls). Eff ect of application timing was determined by response in grain yield, grain N uptake (GNU), leaf chlorophyll meter (CM) reading, and soil NO3 --N measured in early June. Soil NO3 --N concentrations were greater for manure and fertilizer N applied in spring compared with fall and winter application, but the same for both poultry manure sources. Grain yield, GNU, and CM reading response to manure N were not diff erent among either poultry manure sources or application timings. Furthermore, estimated manure plant N availability was not diff erent among poultry manure sources or time of application. Overall fi rst year crop-available N from poultry manure, based on fertilizer N equivalence, using grain yield, GNU, and CM readings was estimated at 43 to 53% of total N. Th e supply of available N to corn was not aff ected by poultry manure application timing despite diff erent lengths of time to crop uptake or delayed incorporation with winter application.

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