Laura E. Lindsey

Climate-induced reduction in US-wide soybean yields underpinned by region- and in-season-specific responses

The United States is one of the largest soybean exporters in the world. Production is concentrated in the upper Midwest1. Much of this region is not irrigated, rendering soybean production systems in the area highly sensitive to in-season variations in weather. Although the influence of in-season weather trends on the yields of crops such as soybean, wheat and maize has been explored in several countries2–6, the potentially confounding influence of genetic improvements on yields has been overlooked. Here we assess the effect of in-season weather trends on soybean yields in the United States between 1994 and 2013, using field trial data, meteorological data and information on crop management practices, including the adoption of new cultivars. We show that in-season temperature trends had a greater impact on soybean yields than in-season precipitation trends over the measurement period. Averaging across the United States, we show that soybean yields fell by around 2.4% for every 1 °C rise in growing season temperature. However, the response varied significantly among individual states, ranging from −22% to +9%, and also with the month of the year in which the warming occurred. We estimate that year-to-year changes in precipitation and temperature combined suppressed the US average yield gain by around 30% over the measurement period, leading to a loss of US

Nitrogen Release from Weed Residue

11 billion. Our data highlight the importance of developing location-specific adaptation strategies for climate change based on early-, mid- and late-growing season climate trends.

Fertilizer and Population Affects Nitrogen Assimilation of Common Lambsquarters (Chenopodium album) and Redroot Pigweed (Amaranthus retroflexus)

Abstract Weed residues can impact nitrogen (N) cycling in agro-ecosystems that primarily utilize POST weed control. Quantifying this potential N source or sink may influence weed control and fertilization practices. A laboratory experiment measured the rate and quantity of N release from common lambsquarters, common ragweed, and giant foxtail. Weeds were grown in the field at four N rates (0, 67, 134, or 202 kg N ha−1) and collected at two weed heights (10 or 20 cm) to give a range of residue chemical composition. Residue chemical composition parameters of carbon ∶ N (C ∶ N) ratio and total N, nitrate-N, acid detergent fiber, and neutral detergent fiber concentration were measured and correlated with N release. Nitrogen release from weed residue mixed with soil was determined over a 12-wk period. Nitrogen was released from all weed residues at 12 wk. Prior to 12 wk, N was immobilized by giant foxtail grown with no N application. Prior to 4 wk, N was immobilized by 20-cm weeds grown with no N application. Nitrogen release from weed residue was negatively correlated with C ∶ N ratio. Weed residue with a C ∶ N ratio of < 19 (weeds grown with N application and 10-cm weeds) released 25 to 45% total N concentration within 2 wk and may contribute N within the growing season. Weed residue with a C ∶ N ratio > 19 (giant foxtail and 20-cm weeds grown with no N) initially immobilized N and may not contribute N within the growing season. Nomenclature: Common lambsquarters, Chenopodium album L. CHEAL; common ragweed Ambrosia artemisiifolia L. AMBEL; giant foxtail, Setaria faberi Herrm. SETFA; corn, Zea mays L.

Effects of Row Spacing and Nitrogen Rate on Wheat Grain Yield and Profitability as Influenced by Diseases

Abstract Weed growth and N assimilation usually increase with N application rate. With the increasing price of N fertilizer, a better understanding N assimilation by weeds is necessary to maximize economic return. Total plant yield is generally independent of population density, except when plants are very small or at very low population density. If plant yield is independent of population density, weed N assimilation may also be independent of population density. However, the effect of weed population density on N assimilation has not been thoroughly investigated. A 2011 controlled-environment study was established in East Lansing, MI, to evaluate the effect of weed population density and N application rate on growth and N assimilation by common lambsquarters and redroot pigweed. Study factors included four weed densities (1, 2, 4, and 8 plants pot−1), three N application rates (0, 67, and 134 kg N ha−1), and two weed species (redroot pigweed and common lambsquarters). Weeds were destructively harvested 3 wk after emergence, and shoot height, biomass, total N concentration, N use efficiency, and N assimilation were measured. Redroot pigweed was taller, had greater shoot biomass, and a greater shoot N assimilation than did common lambsquarters. With similar environmental conditions, redroot pigweed is expected to be more competitive than common lambsquarters. Shoot N assimilation increased with increasing weed population density, indicating that N assimilation was not independent of population density 3 wk after emergence because weeds were small or at low population density. Nomenclature: Common lambsquarters, Chenopodium album L. CHEAL; redroot pigweed, Amaranthus retroflexus L. AMARE

Assessing causes of yield gaps in agricultural areas with diversity in climate and soils

In Ohio, changes in nitrogen (N) fertilizer application rates and row spacing in combination with fungicide applications have been proposed as possible strategies for increasing wheat productivity and profitability. Field experiments were conducted in 2013, 2014, and 2015 to evaluate the benefits of increasing row spacing and N rates in soft red winter wheat as influenced by diseases. Combinations of narrow (19 cm) and wide (38 cm) row spacings, N rates ranging from 34 to 180 kg ha-1, and the fungicide prothioconazole + tebuconazole applied at flag leaf emergence, boot, or early anthesis represented different management programs. Linear mixed model analyses were performed to evaluate the effects of N, row spacing, and fungicide timing on leaf rust, Fusarium head blight (FHB), and deoxynivalenol (DON), and to quantify relationships among leaf rust, N, grain yield (YLD), and test weight (TW). YLD, TW, grain prices and price discounts, as well as input costs were used to estimate net cash income (NCI) for each management program. Wide row wheat had statistically higher mean FHB and DON, and lower mean yield and test weight than narrow row wheat in 2014 and 2015 but not in 2013. There were significant positive linear relationships between leaf rust and N as well as YLD and TW with N. Differences in FHB and DON among N rates were not statistically significant. Leaf rust severity was consistently lower in treated plots, with efficacy influenced by N rate and application timing. Programs with narrow row spacing and treated with the fungicide generally resulted in the highest mean YLD and TW across N rates. Price discounts due to high FDK and DON, and low TW were higher, and consequently, NCIs were lower in 2014 and 2015 than in 2013. The highest NCIs were obtained for programs with the highest YLD and lowest price discounts, consequently programs with wide row spacing, a fungicide treatment, and high N rates were only economically beneficial when FHB levels were low and grain prices were high.