Fertility Management Planning

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Just as measuring and planning can improve sustainability and economics in irrigation, the same goes for your fertility plan. When formulating a nutrient plan, base your fertilizer inputs on realistic yield goals, taking into account recent soil test data (this is critical), soil type, and the field’s fertility history.

Setting realistic yield goals - A realistic yield goal should not exceed 10-20% of the average yield from the last 3-5 years. Many factors can affect the availability of soil nutrients and crop uptake, even when initial soil fertility was optimal. Therefore, applying fertilizer above the realistic assessment of what the crop can use likely will not improve yield above 10-20% and may result in poor resource management and economic losses.

Soil tests are a critical component of nutrient planning. In general, a soil test will indicate if the soil is:

  • Low; a fertilizer addition will likely increase growth and yield
  • High; a fertilizer addition is not likely to increase growth or yield
  • Intermediate; a fertilizer addition may increase growth or yield

As the test result for a nutrient (most notably N, P, or K) increases from very low to very high, the probability of achieving an economic yield response from an addition of that nutrient decreases from very high to very low.

Base fertilizer inputs on soil test results and realistic yield goals - In addition to applying fertilizer to bring the soil nutrient level to the desired values for the region, ideally, fertilizer inputs should also replace what will be removed by the crop based on your yield goal, calculated as crop removal rate (lbs of nutrient/bu) x yield goal (bu/acre). Nutrient removal rates will vary by crop, geography, cropping practice (for example, harvesting grain versus silage), and other factors. Use local sources for nutrient removal rate estimations. Additionally, your fertilizer input should take into account credits from other sources such as nutrients in irrigation water, manure applications, and mineralization from organic matter.

Like other inputs, it is difficult to know where to cut back on fertility when you need to cut costs. To help farmers with these difficult decisions, several of the 2017 demonstration trials at Monsanto’s Gothenburg Learning Center in Gothenburg, NE evaluated how Monsanto corn products respond to various nitrogen (N) management strategies. One demonstration trial evaluated corn product response to either all N applied at planting vs. N applied via fertigation throughout the season.1 They found significantly increased yields in some products when N was applied via fertigation, and decreased yields in other products, suggesting that the response to N can vary by product. In another trial, there was no yield response to a split application of N vs. the same amount of N applied all at planting, nor to an additional application of sulfur and zinc.2 In this trial, initial soil fertility levels were relatively high, suggesting that corn products may not respond much to additional fertility when soil fertility levels are already adequate. A third trial found a significant increase in yields in over 60% of the corn products tested when 120 lbs/acre of N was applied at planting followed by an additional 100 lbs/acre at the V7 growth stage compared to corn products that received only 120 lbs/acre of N at planting.3

These trials suggest that a fertility plan could be tailored to individual products, which may provide further economic and environmental benefits. Monsanto will continue to test products for their responses to a variety of management practices in order to provide farmers with product-specific management solutions.

1 Corn Product Response to Nitrogen Strategy, Learning Center Summary, Technology Development and Agronomy, 171114093428; 2 High Input Corn Management, Learning Center Summary, Technology Development and Agronomy, 171122135613; 3 Corn Product Response to Nitrogen and High Densities, Learning Center Summary, Technology Development and Agronomy, 171201155056

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