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) Compare H3A-4 extractable Ca, Mg, K, Na, S, P, Mn, Zn, B, Fe, and Al; H3A-4 extractable phosphate to routine soil test/ recommendations; (b) Evaluate the relationship between HSHT’s plant available N, HSHT’s mineralizable N (estimated biological N), and alkaline-hydrolyzable N using linear regression analysis; and (c) Evaluate the relationship between HSHT’s Plant available N, HSHT’s estimated biological N, and alkaline-hydrolyzable N to check plot grain yield. 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 while the remaining N was side-dress at the V6 stage corn. The nitrogen fertilizer treatments included: 0, 60, 120, 180, 210, and 240 lb N ac-1. 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.
Results
(a) Relationship between HSHT’s H3A-4 to Mehlich 3 extractable nutrient elements
2021
Mehlich III and H3A-4 extractable nutrients were significantly correlated and showed a positive linear relationship with the combined data across soil depths and locations except Ca. On average, Mehlich-III extracted approximately 75% more P, 36% more K, 78% more Ca, 73% more Mg, 61% more S, 17% more Na, 43% more B, 86% more Fe, 44% more Zn, 93% more Mn, and 83% more Cu than H3A-4 extractable nutrients. The H3A-4 extracting solution consists of a dilute mixture of four weak acids with a weakly buffered pH of approximately 3.75, that may account for the lower concentration of H3A-4 extractable nutrients. Phosphorus, sulfur, boron, and manganese correlated well (R2 = 0.75 – 0.95) while potassium, zinc, copper, iron, and sodium correlated moderately (R2 = 0.39 – 0.61). Although the relationships between some nutrients appear highly correlated, existing calibration and correlation data relating conventional soil test to relative yield may not be appropriate for current mineral fertilizer recommendation.
2023
Mehlich III and H3A-4 extractable nutrients were significantly correlated (R2 = 0.22 – 0.99) and showed a positive linear relationship with the combined data across soil depths and locations except Ca (R2 = <0.01). Phosphorus, magnesium, sulfur, sodium, iron, and manganese correlated well (R2 = 0.75 – 0.99) while potassium correlated moderately (R2 = 0.44). Although the relationships between some nutrients appear highly correlated, existing calibration and correlation data relating conventional soil tests to relative yield may not be appropriate for current mineral fertilizer recommendations.
On average, Mehlich-III extracted approximately 49% more P, 66% more K, 61% more Ca, 71% more Mg, 44% more S, 100% more Na, 46% more Fe, 28% more Mn, and 79% more Cu than H3A-4 extractable nutrients. The H3A-4 extracting solution consists of a dilute mixture of four weak acids with a weakly buffered pH of approximately 3.75, which may account for the lower concentration of H3A-4 extractable nutrients. In contrast, Mehlich 3 extraction has a lower pH of 2.5.
(b) Relationships between HSHT’s Estimated biological N, alkaline mineralizable N, and HSHT’s plant available N
2021
HSHT’s EB-N and HSHT’s PA-N was assessed at preplant for both locations; however, at sidedress (V6 growth stage), HSHT’s EB-N and HSHT’s PA-N was evaluated at only the Jackson location. In this study, the preplant HSHT’s estimated biological N, HSHT’s plant available N, alkaline mineralizable N, in 2023 at both locations ranged from 4.2-26.2, 9.2-34.0, and 33-81, lb N a-1, respectively. Among these three N parameters evaluated in this study, the N content in the AH-N was higher followed by HSHT’s PA-N and then HSHT’s EB-N. At both locations, AH-N, HSHT’s EB-N, and HSHT’s PA-N decreased significantly with depth, where the N content at the 0-6-inch depth was significantly higher than the other depths, but there was no significant difference beyond the 0-6-inch depth. Estimated N contents for AH-N, HSHT’s EB-N, and HSHT’s PA-N at sidedress was lower when compared to the N contents at preplant. Similar to preplant, the AH-N and HSHT’s PA-N were greatest at the o-6-inch depth. However, there was no significant difference beyond this depth regardless of location.
In this study, the HSHT’s Estimated biological N, HSHT’s plant available N, alkaline mineralizable N, in 2023 at both locations ranged from 0.1-14.3, 13.0-36.2, and 55-148, lb N a-1, respectively. Among these three N parameters evaluated in this study, the N content in the AH-N was higher followed by HSHT’s PA-N and then HSHT’s EB-N. At both locations, HSHT’s EB-N and HSHT’s PA-N decreased significantly with depth, where the N content at the 0-6-inch depth was significantly higher than the other depths, but there was no significant difference beyond the 0-6-inch depth. Similarly, the highest N content for AH-N at both locations was observed at the 0–6-inch depth. In contrast to HSHT EB-N and HSHT PA-N, significant differences in N contents were observed among depths beyond the 0–6-inch depth.
(c) Relationship between HSHT’s Plant available N, HSHT’s estimated biological N, and alkaline-hydrolyzable N to check plot grain yield
2021
At preplant, the best predictive relationship between the check plots and AH-N was found at the 6-12-inch depth (R2 = 0.57). In contrast, the correlation between the check plots and EB-N was not significant at all depths.
2023
Correlation of grain yield of the check plots with AH-N resulted in a significant and positive linear regression model (R2 = 0.38 – 0.83) for all depths, with the best predictive relationship at the 0-18-inch depth (R2 = 0.83). With the exception of the 0-6 and 0-24-inch depths, a strong correlation was observed for the other depth. In contrast, a strong relationship was not observed between grain yield from the check plots and HSHT’s Plant available N or HSHT’s estimated biological N.
