Delaware Agronomy Blog

University of Delaware Cooperative Extension

Category: Fertility (page 1 of 4)

Grid Sampling Soils for Variable Rate Lime Applications

Jarrod Miller, Extension Agronomist & James Adkins, Irrigation Engineer

One method to uncover soil variability and crop response is to use precision soil sampling, including either grid or zone methods. These maps can then be used to make variable rate applications, where application rates will change as you cross the field, and GPS helps guide the rates. For this study, soil samples were taken from the upper eight inches of soil on our irrigation research farm in Harbeson, DE. Samples were taken on a 90 by 90-foot grid in April 2022 (Figure 1).

Figure 1: Grid sampling points overlain onto a September 2024 image of the Warrington Irrigation Research Farm, including both center pivot and linear irrigation.

From these grids, maps of nutrients and soil properties were created, including soil pH and buffer pH (Figure 2). Soil pH is measured using water and is the pH your crop will react to. So you use the soil pH measurement to decide if you want to raise or lower your pH. The buffer pH helps figure out any acidity within the soil that will react with lime, causing the need for a higher lime rate (Figure 2b). These two pH measurements were combined using UD recommendations to create a variable rate lime map (target pH = 6.2), which was applied in 2023.

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Using NDVI to Determine Early Vegetative Growth and Nitrogen Needs

Jarrod Miller, Extension Agronomist, University of Delaware

Precision nitrogen (N) management through the use sensors has been used to improve nitrogen use efficiency (NUE) for field crops by estimating corn needs during early growth stages (Aula et al., 2020; Cao et al., 2017) Indices have been developed using specific wavelengths of light, such as the normalized difference vegetation index (NDVI) to estimate plant biomass and correlate it to N needs (Holland et al., 2012; Raun et al., 2005a; Dellinger et al., 2008). The use of NDVI has allowed for reductions in N application have been performed without reducing crop yield (Barker and Sawyer, 2012; Aula et al., 2020).

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Corn Yield Responses to In-furrow Biological Products

James Adkins, Extension Engineer, adkins@udel.edu,  Jarrod Miller, Extension Agronomist

In 2023, the University of Delaware evaluated the corn yield response to 14 biological products at 3 nitrogen fertility levels (optimum, 80%, and 50% rate).  While some of the products claimed to provide nitrogen fixation others were designed to improve plant health and root structure.  Products tested include:        

Invigorate (AMVAC)   

Ion Strike (Planet Earth Agronomy)

Zypro (Helena)   

BioGrowth (Willard Ag)

UtrishaP (Corteva)     

Source (Sound Ag)

ProveN40 (Pivot Bio)   

Blaine (Farmer 2 Farmer)

Accomplish Max (Loveland)     

Blaine with humic (Farmer 2 Farmer)

RioZyme Supreme (Schaeffer’s)   

Nexia (Innvictis)

RioZyme Plus (Schaeffer’s)     

Launch (Ag Concepts)

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Potassium Applications in Delaware Soils

Jarrod Miller, Extension Agronomist

University of Delaware recommends potassium (K) applications for low (0-70 ppm) and medium (71-140 ppm) soil test categories. However, soils in Delaware may have K that is not accounted for in a normal soil test, with minerals slowly release K over the growing season. Some of this was established by UD soil chemists in the 1980s, who observed high total K (not all plant available) in our soils, particularly in the sand fraction (https://www1.udel.edu/soilchem/Parker89SSSAJa.pdf). This means that some soils may need less K than is recommended by a regular soil test.

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Biological Nitrogen Contributions Across Multiple Nitrogen Rates

Quick summary: There was no boost in yield or tissue N from Pivot-Bio additions, however we did observe higher levels of Mn in corn ear leaves with the biofertilizer. Yield may have been limited by something other than N.

To examine Nitrogen (N) contributions from biological fertilizer amendments, Pivot-Bio was added across a range of N-rates (0-330 lbs/acre) in the spring of 2023. The irrigated plots were harvested in October where yields ranged from 50 to 200 bushels per acre (Figure 1). The only statistical difference in yield was 0 N with pivot bio, which was lower than all other treatments. A dry cool May potentially reduced N availability in 2023, and heavy rainfalls and field saturation may have also limited yields. Drone imagery taken during the season will be analyzed at a later date to determine when yield may have become limited.

Figure 1: Yields based on Nitrogen rates and Pivot-Bio additions.
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