Crop and Fertilizer Management to Overcome Yield Barriers in Continuous Corn

Potential corn yield is that of a hybrid when grown in a suitable environment with optimal management in the absence of stresses from nutrients, water, and pests. Past high-yield research has focused on grain yield as the primary indicator of performance; however, fertilizer use efficiency is also important for economic and environmental viability.

Advanced fertilizer management ensures that supplies of all nutrients are adequate to meet the demands of the crop throughout the entire growing season, and achieves high fertilizer use efficiency through optimization of fertilizer source, rate, time, and placement. Nitrogen is often the most limiting nutrient for corn production and is frequently applied in excess and far in advance of rapid corn uptake. This leads to low corn recovery of applied N and risk of N loss, which carries environmental and economic consequences. Enhanced synchrony of N application timing and rate with corn requirements is key to enhancing corn uptake of applied N, thereby improving yield and reducing N loss.

A two-year field study was conducted by Dr. Jeff Coulter and Jeff Vetsch of the University of Minnesota as part of the Pioneer Crop Management Research Award program. The goal of this study was to identify and better understand agronomic practices that increase corn yield and reduce risk of N loss, thereby enhancing profitability. This was evaluated in continuous corn, which requires more intensive management for high yield and has greater risk of N loss compared to a corn-soybean rotation.

Objectives

1. Determine the corn yield levels attainable with intensive management.
2. Compare the performance of advanced fertilizer management and intensive agronomic management systems to those with standard practices in line with university guidelines.
3. Assess whether university fertilizer guidelines can attain yields at levels close to yield potential.

This project compared two agronomic systems:

For both systems, standard fertilizer management in line with university guidelines was compared to advanced fertilizer management. Within these four main-plot treatments, split plots were with and without N fertilizer for evaluation of N use efficiency parameters.

Field experiments were conducted at Waseca, MN in 2019 and 2020 on rainfed tile-drained Nicollet clay loam soil. Treatments were applied to the same plots each year.

Compared to normal agronomics, the intensive agronomics treatment included partial removal of corn stover after harvest, planting a longer-season corn hybrid at a higher planting rate, and applying foliar fungicide at tasseling. The advanced fertilization treatment included P and K application based on grain removal and soil-test levels, surface-banded starter fertilizers, a greater total N rate, and two in-season N applications. Complete treatment details are listed in Table 1.

Treatments were replicated four times in plots that were eight rows wide by 50 feet long. Corn was planted in 30-inch rows in early May in both years. Final corn populations were 34,000 and 39,000 plants/acre for the normal and intensive agronomic treatments, respectively. Weeds were controlled using pre- and post-emergence herbicides. All fertility treatments included a broadcast sulfur application of 25 lbs/acre S and an in-furrow starter fertilizer (10-34-0) of 5 lbs N and 16 lbs P₂O₅/acre.

Residue management and tillage practices for all treatments included shredding of stalks at harvest, fall tillage with a disk ripper, and a spring tillage pass with a field cultivator. Plots were harvested at physiological maturity to determine grain yield and moisture content. Agronomic N use efficiency was calculated as:

In both years, there was adequate rainfall for corn growth throughout the growing season. Monthly average air temperature in May, June, and August was relatively cool in 2019. This contributed to lower grain yields in 2019. In comparison to 2019, rainfall during 2020 was relatively low during April and September, but it was adequate for corn growth and was evenly distributed during May through August.

Compared to 2019, average monthly air temperature was similar in 2020, except for June and July which were warmer, and September which was cooler. Collectively, these weather conditions in 2020 resulted in excellent kernel set and a prolonged grain-filling period, which led to very high grain yield (average = 261 bu/acre for the treatment with advanced fertilizer management plus intensive agronomic management).

Averaged across the treatments, corn grain yield was 189 and 230 bu/acre in 2019 and 2020, respectively (Figure 1). Lower grain yield in 2019 is attributed to green snap (about 5% of plants in the normal agronomics treatment and about 6–10% of plants in the intensive agronomics treatment), a cool and wet May that slowed early vegetative growth, and wet conditions due to above-normal rainfall throughout the growing season following a wet fall in the previous year.

In 2019, grain yield was greatest with advanced fertilizer management and either normal or intensive agronomics (average = 196 bu/acre). The yield of these treatments averaged 8% greater than that with standard fertilizer management. However, in 2020, advanced fertilizer management plus intensive agronomics produced the highest grain yield (261 bu/acre), which was 10% higher than that with advanced fertilizer management plus normal agronomics. In 2020, compared to standard fertilizer management, grain yield with advanced fertilizer management was 20% greater under normal agronomics and 16% greater under intensive agronomics.

In 2019, kernel weight was not significantly different among treatments, while the greatest kernel number occurred with advanced fertilizer management and either level of agronomic management, or with standard fertilizer management plus intensive agronomics (Table 2). In 2020, there was a similar pattern in grain yield and kernel number among the treatments, as the highest values occurred with advanced fertilizer management plus intensive agronomics and the lowest values occurred with standard fertilizer management plus normal agronomics (Table 3).

Kernel weight in 2020 was greater with advanced compared to standard fertilizer management for both levels of agronomics. Across both study years, increased kernel number consistently boosted grain yield, while heavier kernels were associated with greater grain yield in only the highest-yielding year of 2020, where the maximum yield was 261 bu/acre (compared to 2019 where the maximum yield was 199 bu/acre).

Grain yield was greater with advanced compared to standard fertilizer management. When advanced fertilizer management was used, grain yield was not greater with intensive agronomics (i.e., partial stover harvest, longer-season hybrid, higher planting rate, and foliar fungicide) in 2019, but it was in 2020.

Fertilizer and field operation costs at Waseca were $71.58 greater with advanced fertilizer management compared to standard fertilizer management. When intensive agronomic management was used, the increase in grain yield with advanced fertilizer management compared to standard fertilizer management in 2019 (average = 14 bu/acre) was not enough to offset the increased treatment cost. Therefore, greatest net economic return in 2019 at Waseca occurred with standard fertilizer management plus intensive agronomics. However, net return with advanced fertilizer management plus intensive agronomics was only $9.97/acre less than that with standard fertilizer management applied to intensive agronomics in 2019.

The exceptionally favorable growing conditions in 2020 resulted in high grain yield and relatively low grain moisture at harvest. Under these conditions, grain yield and net economic return were greatest with advanced fertilizer management plus intensive agronomics.

Advanced fertilizer management plus normal agronomics produced the second-highest grain yield but third highest net economic return in 2020, while standard fertilizer management plus intensive agronomics produced the third-highest grain yield but second-highest net economic return in 2020; this was due to greater treatment cost for advanced compared to standard fertilizer management ($71.58) than for intensive agronomics compared to normal agronomics ($32.50).

Averaged across both years, partial net economic return was greatest with advanced fertilization plus intensive agronomics ($749.00/acre).

This value was $42.68/acre greater than that with standard fertilization plus intensive agronomics, $100.30/acre greater than that with advanced fertilization plus normal agronomics, and $146.67/acre greater than that with standard fertilization plus normal agronomics.