How Corn and Soybean Yields Fared by County in 2012 - UNL CropWatch, June 28, 2013
June 28, 2013
2012 Irrigated Corn and Soybean Yields 2nd Highest in History
Corn/Soybean Ratio Indicates Dryland Soybean Performed Slightly Better than Dryland Corn under Drought Conditions
Early this year USDA-NASS released statistics on irrigated and dryland corn and soybean yields in Nebraska for the 2012 crop season. According to the data, Nebraska state average yields of corn and soybean were 190 bu/ac and 59 bu/ac under irrigation, and 61 bu/ac and 25 bu/ac under dryland conditions (Figures 1 and 2). Although yields of irrigated corn and soybean were the second highest in history (only slightly below the record yields in 2009 for corn and 2011 for soybean), the 2012 season was the worst year for dryland corn and soybean since 1983 (corn) and 1984 (soybean) (Figure 3). The low dryland yields were not surprising given that the rainfall during the crop growing season did not exceed 10 inches at most locations, which is about half of the rain amount in a typical year.
The Nebraska average yield for irrigated corn in 2012 was 190 bu/ac, 10 bushels above the 2011 yield and 5 bushels above the average for the past seven years (2005-2011). Highest county-level average irrigated corn yields were reported in south central Nebraska and ranged from 205 to 220 bu/ac (Figure 1). In contrast, 2012 was a very bad year for dryland corn, with a statewide average of 59 bu/ac, 74 bushels below the 2011 state average for dryland corn, and 68 bushels below the past seven-year average (2005-2011). The highest county-level average dryland corn yields, in the range of 80 to 100 bu/ac, were reported in counties on the east central and east south edges of the state and in two counties in south central Nebraska (Figure 1).
Nebraska statewide irrigated soybean yield in 2012 of 60.7 bu/ac was only 0.4 bushel below the 2011 irrigated soybean average and 2 bushels above the past seven-year average (2005-2011). The highest county-level average irrigated soybean yields, in the range of 66 to 70 bu/ac, were reported for counties in south central Nebraska (Figure 2). Similar to dryland corn, it was also a bad year for dryland soybean, averaging a statewide 25 bu/ac, which was 23 bushels below 2011 average, and 20 bushels below the past seven-year average (2005-2011). The highest county-level average dryland soybean yields, in the range of 32 to 38 bu/ac, were reported for counties in the east central and east south edges of the state and for two counties in south central Nebraska (Figure 2).
The corn/soybean yield ratio in Nebraska irrigation systems is typically about 3.2, but it is only 2.8 for dryland cropping systems (Figure 4). There are two main reasons why the productivity of corn is higher than for soybean. First, corn has a C4 photosynthetic mechanism, which makes it more efficient than C3 crops such as soybean. Second, there is a marked difference in grain composition: corn grain is mostly composed of carbohydrates while soybean seed is rich in oil and protein. The 3.2 and 2.8 corn/soybean yield ratios can be used to benchmark yields in a given region or year. If the corn/soybean ratio under a given water regime departs significantly from the value indicated above for the same water regime, this indicates sub-optimal management and/or unfavorable soil/weather conditions for one of the crops.
In 2012, the corn/soybean ratio was 3.1 and 2.3 for irrigated and dryland crops. While the 2012 ratio of 3.1 for irrigated crops was consistent with the long-term average irrigated ratio (3.2), the 2012 ratio for dryland crops of 2.3 was well below the long-term dryland average (2.8) (Figure 4). This means that dryland soybean was relatively less affected by the 2012 drought compared with dryland corn. A possible explanation for the better performance of dryland soybean, compared with dryland corn, is that the soybean pod and seed-filling period occurred in August under relatively cooler and wetter conditions, compared with the hotter and dry conditions of July when pollination and kernel set of corn occurred. Also, soybean has a wider flowering and grain setting window than corn, which gives soybean plants more plasticity to compensate for the impact of transitory periods of water stress.
Patricio Grassini, Research Associate Professor, UNL Agronomy and Horticulture
James Specht and Haishun Yang, Professors, UNL Agronomy and Horticulture
Keith Glewen and Jenny Rees, UNL Extension Educators