Evaluation of soil parameters and diagnostic tools to assess nitrogen and sulfur response in corn and wheat

Abstract

Sulfur fertilization is receiving more interest, with sulfur deficiencies showing up in crops including corn and wheat. Decreased atmospheric deposition and higher yields have driven the need for sulfur fertilization. Two studies were conducted to evaluate nitrogen (N) and sulfur (S) responses. The objectives of the first study were to assess the effects of nitrogen sources and sulfur rates on yield, nutrient uptake, and nutrient use efficiency terms on corn (Zea mays L.) production. Nitrogen and S concentrations in corn biomass and grain were evaluated, and N and S use efficiency indicators were calculated at five locations in 2019 and 2020. The experiment was set up in a randomized complete block design with seven treatments and four replications. Treatments included a control with no fertilization, three fertilizer treatments evaluating sulfur rates, and three evaluating N sources. Fertilizer treatments were balanced to 202 kg N ha⁻¹. Fertilizer treatments were sidedress applied on the soil surface before V6 growth stage. Organic matter greatly impacted nutrient use efficiency indicators, including agronomic efficiency (A.E.), apparent recovery efficiency (R.E.), and internal efficiency (I.E.). The impact of S rate and N source on yield was not statistically significant across locations, but yields at locations 1 and 2 trended higher with added sulfur fertilizer at increments of 17, 31, and 52 kg S ha⁻¹. Nitrogen fertilizer resulted in a significant increase in post-harvest soil nitrate compared to the control, but there was no significant difference between N source and S rate. The second study focused on wheat (Triticum aestivum L.) response to S affected by soil characteristics. The objectives of this study were to evaluate plant uptake of S and N with added S fertilizer and the effect of soil parameters on wheat response to S. A greenhouse study was conducted utilizing 15 soils from Kansas and Nebraska. Fertilizer treatments included Urea Ammonium Nitrate (UAN) (28-0-0; N-P₂O₅-K₂O) at 0.99 mL UAN pot⁻¹ (300 kg N ha⁻¹) to all pots, and half of those pots had micronized elemental sulfur (0-0-0-50S; N-P₂O₅-K₂O-S) at 0.19 mL (100 kg S ha⁻¹). All fertilizers were topdress applied using a metered pipet. A randomized complete block design was utilized using three replications for each N and N plus S fertilizer treatment. Pre-fertilization soil samples were analyzed for properties including Soil Organic Matter (S.O.M.), Cation Exchange Capacity (C.E.C.), pH, soil texture, phosphorous, potassium, zinc, total carbon, total nitrogen, and soil test sulfur. The average whole plant wheat sulfur uptake (WPU-S) was increased with the application of sulfur fertilizer for many soils in this study. The main soil variables determining plant response to S fertilizer were soil test phosphorus, soil organic matter, cation exchange capacity, and sand content. Higher soil test phosphorus (STP) and sand content contributed to greater plant response and uptake of sulfur from applied S fertilizer. In contrast, higher soil organic matter and cation exchange capacity resulted in smaller plant response to applied S fertilizer. Thus, the traditional soil test S showed a low correlation with plant response in our study. These results suggest that a more accurate prediction of wheat response to S fertilizer may be accomplished considering multiple soil parameters.