By Mark Licht, Extension Cropping Systems Agronomist; Sotirios Archontoulis, Assistant Professor

As the saying goes, hindsight is 20/20; perfect vision. We often say “if we knew the weather, then we can provide the best recommendations.” 

Usually, we do not know the weather or we do not have the appropriate tools in place, so the questions remain unanswered. Now that we know the weather, the next important question is to determine what could have been done differently in 2015. This is an important part of understanding and evaluating production and environmental performance of our crop management decisions. 

In this article, we leverage our knowledge of the 2015 weather and use the Agricultural Production Systems sIMulator (APSIM) cropping system model as a framework to explore alternative management options to the cropping systems used in the Yield Forecast project in an effort to understand what could have helped improve corn and soybean yields more in 2015.

For the scenario analysis we used the eight cropping systems from the Yield Forecast Project (see table descriptions below for the default management practices) and the APSIM model to evaluate the impact of changing the nitrogen (N) rate, timing of N application, seeding rate, row spacing, crop maturity and water supply through irrigation. By running the cropping system model with adjustments to crop management, it can be determined if and how much grain yield, N loss and net return could have been improved in 2015. This scenario analysis also shows the trade-offs that exist between profitability and environmental performance and provides an opportunity to identify those practices that could provide a win-win situation by reducing N losses to the environment and increasing net profits.

In the Ames corn cropping systems (Table 1), N losses were reduced by either applying N later in season (4-8 weeks after planting) or reducing N applications (scenarios 3, 6, and 7). However, reduced N application rates also resulted in a detrimental impact to both yield and net profits for both early and late planting dates. Changes to seeding rate and row spacing had little effect on yield, N loss or net return. Increasing maturity increased both yield and net profits while having minimal reductions of N loss when no additional N was applied. 

The response to alternative management was different between early and late planting. This reveals the complexity that exists in the soil-crop-atmosphere system and that every field by management practice should be treated as a unique system. Among the scenarios evaluated, scenarios 2, 11, and 14 resulted in win-win situations (more profits with less environmental damage) for both early and late planting corn. These scenarios shifted the N application later, from 30-inch to 20-inch row spacing, or used a longer maturity corn hybrid.

In the Sutherland corn cropping systems (Table 2), the trends were the same for scenario impacts on both the early planted and late planted systems. Applying two third less N had minimal impacts on yield, but reduced N losses and increased net profits. This is because at Sutherland, the initial soil nitrate at planting time was exceptionally high (20 ppm NO₃-N at 1 feet). In contrast, at the Ames site, the soil nitrate at planting time was around 5 ppm NO₃-N. Reducing row spacing to 20 inches increased yields and net profits will reducing N losses. 

Irrigation had positive effects on yields and net profits but also increased N losses. And planting a longer maturity without additional N balanced yield and net return while not changing N losses.

In the Ames soybean cropping systems (Table 3), the largest benefits came from reducing the row spacing from 30-inch rows to 15-inch rows (scenarios 5 and 6) and planting a later maturity in combination of a higher seeding rate and narrower row spacing (scenario 9). 

However, planting a shorter maturity soybean resulted not only in reduction in yield and net return but also increased N loss, especially for the late planting date. It is worth mentioning that the combination of late planting soybean and longer maturity substantially increased the risk of fall frost and delayed harvest. In 2015, this was not a problem, but in other years this could be a problem.

In the Sutherland soybean cropping systems (Table 4), results were very similar to that of the Ames soybean cropping systems. Soybean yield, net returns and N loss benefits were realized by reducing row spacing to both 15-inch and 20-inch row spacing (scenarios 4, 5 and 6) and by increasing soybean maturity in combination with increasing seeding rate and decreasing row spacing (scenario 9). Coincidentally, at Sutherland where rainfall was limited during a portion of the growing season (July), irrigation had only slight yield benefits but increased N loss (scenarios 10, 11, and 12).

In summary, combined net benefits for yield, N loss and net return in the corn cropping systems were realized from adjusting either the timing or rate of N application and by planting a slightly longer corn maturity. In the soybean cropping systems, the largest combined benefits resulted from narrower row spacing and fuller season soybean varieties.

This type of analysis offers unique opportunities to understand how the system responds to “what-if” management questions and provides the means to evaluate concurrently production and environmental performance of cropping systems. However, it should be noted that this analysis is specific for weather and management practices used in 2015. Future management decisions should be made using pre-season decision support tools that include weather components that can factor in additional variability to ensure robust decision can be made.