Predicting Corn N response using Alkaline Mineralizable N and Haney Soil Health Tool-N
Research was funded by Southern SARE
Nutifafa Adotey, Assistant Professor & Soil and Nutr. Magt Specialist Xinhua (Frank) Yin, Professor & Cropping System Scientist, University of Tennessee, and Ryan Blair, Extension Area Specialist III and County Standardized Trials Specialist
Introduction
Nitrogen management in corn production in the US is essential considering more than half the total N fertilizer used in the US is applied in corn production. Given the substantial investment in N fertilizer and its potential environmental risks, implementing best N management practices has potential to improve efficiency and profitability of applications. Nitrogen fertilizer recommendations for corn in TN as well as most southern US are determined from N response trials and modified based on soil type, previous crop and crop production history. Current N fertilizer recommendation does not account for potentially mineralizable N; hence, there is a possibility for either over or under application of N fertilizer. Limited information is available on the adequacy of alkaline mineralizable N or the mineralizable component of Haney test to predict corn response to N on replicated small plots in producer field in southern US. A crop response to mineralizable N may help develop a site-specific N fertilizer recommendation tool for corn, thus avoiding over or under application of N fertilizer. Replicated small plot on-farm trials are on-going at two locations in west TN to address the adequacy of alkaline mineralizable-N and HSHT -N to predict corn N needs”. The objectives of the on-farm trials include: (1) evaluating the relationship alkaline mineralizable N and HSHT to corn response, (2) developing N fertilizer rate calibration using alkaline-hydrolyzable N, and (3) comparing current UT fertilizer recommendation, HSHT N fertilizer recommendation, and alkaline-hydrolyzable fertilizer recommendation.
Materials and Method
Two replicated on-farm trials were conducted at Jackson, TN and Milan, TN from 2021 to 2023 to address the adequacy of alkaline mineralizable-N and HSHT-N to predict corn N needs. Prior to fertilizer application, six core samples were collected from each plot at 0-6 and 6-12-inch depths and analyzed for routine chemical properties. In addition, core samples were collected from the 0 lb N ac-1 plots at four depths 0-6, 6-12, 12-18, 0-18, and 0-24 inches at sidedress for soil health characterization and alkaline-hydrolyzable N. The soil health was characterized using the Haney Soil Health Tool at three depths: 0-6, 6-12, and 12-18 inches. Soil health parameters measured 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 were analyzed by Brookside Laboratories Inc. The alkaline-hydrolyzable N was evaluated at 5 soil depths 0-6, 6-12, 12-18, 0-18, and 0-24 inches using the method by Roberts et al., (2011). All samples were analyzed by the N-Star Soil Testing Laboratory. Data from soil analysis to (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, and (c) Evaluate the relationship between HSHT’s plant available N, HSHT’s mineralizable N (estimated biological N), and alkaline-hydrolyzable N using linear regression analysis. Corn was planted to achieve a final stand of approximately 32,000 – 33,000 plants per acre. Plots were four rows wide x 30 feet long and each treatment combinations were replicated four times in a randomized complete block design. At planting, 60 lb N/acre was hand applied as ANVOL®-treated urea. Side-dress N was hand broadcast at the V6 stage corn at respective application rates on. Nitrogen was applied as a two-way split (at planting + sidedress). The nitrogen fertilizer treatments included: 0, (60 + 0), (60 + 60), (60 + 120), (60 + 150), and (60 + 180) lb N ac-1. At tassel, a composite leaf sample consisting of 15 youngest fully matured leaves were collected for tissue N. At maturity, the two center rows of corn in each plot were harvested by hand and then threshed using a small plot combine harvester with an automatic weighing scale and a moisture meter. Standard agronomic and pest management practices were based on University of Tennessee recommendations.
