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.

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.

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.