Predicting Corn N Response Using Alkaline Mineralizable-Nitrogen and Haney Soil Health Tool-Nitrogen in TN

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Commodities

• Agronomic: corn

Practices

• Crop Production: nutrient management

“A replicated small plot on-farm trial will be conducted at two locations in west TN to address the adequacy of alkaline mineralizable-N and HSHT -N to predict corn N needs”.

The specific objectives of the on-farm trials include: (1) evaluate the relationship alkaline mineralizable N and HSHT to corn response, (2) develop N fertilizer rate calibration using alkaline-hydrolyzable N, and (3) compare current UT fertilizer recommendation, HSHT N fertilizer recommendation, and alkaline-hydrolyzable fertilizer recommendation.

Two-year field trials will be established at two on-farm locations in west TN. Proposed tasks for the on-farm trials include: 1) Soil property characterization and field trial, 2) Soil health assessment (Haney test) and alkaline-hydrolyzable N (University of Arkansas’ N-ST*R) determination, 3) collection of yield data, 4) Extension efforts to engage producers in project.

Task 1. Soil property characterization and field trial:

The experiment will be laid in a randomized complete block design using 6 nitrogen fertilizer treatments with four replications (n = 24). Experimental plots will be 10 x 30 ft² comprising of four rows. Nitrogen will be applied as a two way split (at planting + sidedress). The nitrogen fertilizer treatments include: 0, (60 + 0), (60 + 60), (60 + 120), (60 + 150), and (60 + 180) lb N ac^-1. At planting, 60 lb N ac^-1 of ammonium nitrate will be surface broadcast by hand on all the plots with the exception of the 0 lb N ac^-1 plots. Side-dress N treatments, using ANVOL-treated urea, will be surface broadcast by hand between the fourth to sixth (V4 - V6) leaf stages culminating in a plot total of 60 - 240 lb N ac^-1.  Preplant and post-harvest composite soil samples will be collected from all plots at 2 depths; 0-6 and 6-12 inches using soil auger. The soil samples will be air-dried, sieved through a 2-mmh sieve, and analyzed for soil pH, soil organic matter, texture, Mehlich I extractable soil test nutrients, inorganic nitrate-N and ammonium-N. Phosphorus, potassium, sulfur and zinc fertilizer recommendations at each trial location will be based on soil test results. DeKalb corn will be planted at both trial locations to a stand of 32,000 – 34,000 plants per acre. Standard agronomic and pest management practices during the growing season will be based on University of Tennessee recommendations for unirrigated corn.

Task 2. Alkaline-hydrolyzable N (University of Arkansas’ N-ST*R) and Soil health assessment (Haney Soil Health Tool):

Preplant and sidedress soil samples will be collected from the 0 lb N ac^-1 plots at four depths 0-6, 6-12, 12-18, and 18-24 inches. The soil collected at all the depths will be analyzed for alkaline-hydrolyzable N (Roberts et al., 2011). However, the soil health using the Haney Soil Health Tool will be evaluated at three depths: 0-6, 6-12, and 12-18 inches. Soil health parameters will include soil pH (1:1), buffer pH, soluble salts (1:1); organic matter (LOI); H3A-4 extractable Ca, Mg, K, Na, S, P, Mn, Zn, B, Fe, and Al;  H3A-4 extractable phosphate; H3A-4 extractable available nitrogen (NH₄⁺-N and NO₃^--N); water extractable organic carbon, water extractable total nitrogen; soil respiration (IR Gas Analyzer), and overall soil health score. All samples will be analyzed at a commercial soil testing laboratory. The specific objectives within this task include

(a) Estimate plant available N from HSHT test (H3A-4 extractable available nitrogen + N release). The N release is a function of the mineralizable N and will be computed using water extractable organic carbon, water extractable total nitrogen, and soil respiration.

(b) Compare H3A-4 extractable Ca, Mg, K, Na, S, P, Mn, Zn, B, Fe, and Al; H3A-4 extractable phosphate; H3A-4 extractable available nitrogen (NH₄⁺-N and NO₃^--N) to routine soil test/ recommendations.

(c) Evaluate the relationship between HSHT’s plant available N, HSHT’s mineralizable N, and alkaline-hydrolyzable N using linear regression analysis. 

Task 3. Collection of agronomic and yield data:

Tissue N concentration will be estimated from a composite leaf sample consisting of 15 youngest fully matured leaves at tasseling (VT). The central two rows of each plot will be harvested using a customized small plot combine harvester (Wintersteiger, Inc., Salt Lake City, UT). The specific objectives within this task include

• Estimate the N rate required to attain the relative maximum grain yield at each location using the quadratic-plateau regression.
• Correlate HSHT’s mineralizable N and alkaline-hydrolyzable N to check plot grain yield.
• Develop N fertilizer rate calibration using alkaline-hydrolyzable N.
• Compare current UT fertilizer recommendation, HSHT N fertilizer recommendation, and alkaline-hydrolyzable fertilizer recommendation.

Task 4. Extension efforts to engage producers in project:

The project extension activities are geared toward bringing real solution on optimizing N fertilizer to the front door of agricultural producers, small business owners, fertilizer companies, crop consultants, and consumers to increase the success of farmers, ranchers and small/rural businesses. New information gathered from trials will be communicated through traditional and new avenues, including county meetings with University of Tennessee county extension agents, chemical and fertilizer companies, and producers, in-service training, field tours, popular press, blog/newsletter, and web-based extension publications