Herman J. Kandel

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

Producer participatory spring wheat variety evaluation for organic systems in Minnesota and North Dakota

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.

Spring wheat cultivar harrowing evaluation in Minnesota.

Summary Organic producers in Minnesota and North Dakota, USA, indicated that they wanted to participate in hard red spring wheat (Triticum aestivum L. emend. Thell) variety evaluations. The objectives were to determine if a farmer–researcher developed scoring system could be used to rank wheat varieties for yield potential when grown in certified organic fields, identify views of organic producers about on-farm research, and identify the educational impact of the participatory variety evaluation process. Hard red spring wheat varieties were compared for grain yield at six locations on certified organic farms in Minnesota and North Dakota over a three-year period. A scoring system was developed and then used to identify the relative rank of adapted varieties for yield. Producers were asked to rank all varieties on a scale from 1 to 9, where 1 is lowest yield potential and 9 is highest yield potential. Producers were able to distinguish higher producing varieties as a group in 2003 and 2004. ‘Oklee’ a high yielding variety was ranked lowest in 2005. There was a significant linear relationship between producer ranking and yield (P < 0.05) even though producers could not pick the highest yielding varieties consistently in the field. The producer survey showed that grain yield, protein content, wheat scab resistance, leaf disease resistance, early seedling vigor, test weight and canopy closure were traits producers valued most in a variety. Heading date, impact on succeeding crops, straw and stubble production were ranked lower. Multi-year variety evaluation on certified organic land was highly valued by the producers surveyed. From an educational perspective, the exercise was successful in that producers had to observe individual varieties carefully in order to come to a consensus producer ranking. The model of participatory research can be used for a variety of field research projects and field days.

Wheat Cultivar Performance on Certified Organic Fields in Minnesota and North Dakota

Weed control is a major management issue in the production of spring wheat (Triticum aestivum L.). Harrowing can be used in an integrated weed management program. The objectives of this research were to determine initial plant density, plant density reduction, spike density, yield, and the relationship between plant and spike density with yield of spring wheat cultivars after harrowing on a certified organic farm with farm size equipment near Fertile, MN, in 2003 to 2005. Averaged across cultivars, there was a 16, 8, and 12% reduction in emerged seedlings relative to planted live seeds in 2003, 2004, and 2005, respectively. Post-emergence harrowing reduced plant density by 46% in 2003 (harrowed 2×), 16% in 2004 (harrowed 2×), and 25% in 2005 (harrowed 1×). Post-harrowing plant density and yield were positively correlated in 2003, uncorrelated in 2004, and negatively correlated in 2005. There were differences in yield among the tested cultivars. No cultivar could be identified with consistent lower plant density reduction percentage after harrowing. Our suggestion is to adjust the live seeding rate to locally recommended established wheat plant density, by considering anticipated plant loss before plant establishment (average is 12%), and plant density reduction from post-emergence harrowing (average is 29%).