Integrating water-saving technologies with optimized nutrient management strategies provides opportunities for sustainable agriculture in the Mississippi Delta. Three studies were conducted to determine the effects of irrigation systems, row patterns, and nutrient management strategies on corn and soybeans. The first study determined the effects of irrigation, row pattern, and nitrogen (N) placement methods on corn (Zea mays L.) productivity and N use efficiency. The effects of N placement methods were only evident in 2021 when the rainfall events were more pronounced than in 2020. Regardless of the row pattern, placing N with one knife increased corn grain yield and the agronomic N use efficiency by 14.1% and 16.8%, respectively, when compared to the surface dribble method. The second study investigated the effects of irrigation systems and row patterns on grain yield, grain quality parameters, and irrigation water use efficiency (IWUE) on soybeans (Glycine max L.) grown on Sharkey clay. When irrigation was triggered at -80 kPa, furrow-irrigated soybeans produced 3.9% more grain yield compared to sprinkler-irrigated soybeans. The total amount of water applied by the sprinkler irrigation system represented 19-52% of the total amount applied by the furrow system. Narrow-row patterns achieved greater IWUE than single-row patterns. In the third study, we evaluated the effects of N and irrigation levels on grain quantity, quality, and plant growth on corn grown across different soil electrical conductivity (EC) levels and its implications for variable rate technology. Corn grain yields increased with the increase of N and irrigation levels but decreased as soil EC decreased. Overall, maintaining a sprinkler irrigation threshold between -40 and -70 kPa optimized corn yield. In addition, these results did not provide enough evidence to use variable rate irrigation or variable rate N application in the Mississippi Delta.

Selection of optimum nitrogen (N) fertilizer timing, rate, and placement strategies by corn (Zea mays L.) producers are among their most important annual management decisions. Much research has been conducted on pre-plant, at-plant, and one or more sidedress timings for N application to corn, but few public-sector studies employ modern technological approaches for N placement in their experimental designs. Research gaps on optimum placements for at-plant N systems are especially acute when N banding quantity exceeds 20% of the intended season-long N rate. Previous sidedress research has rarely utilized modern N placement tools with high clearance delivery devices for early and late in-season sidedress timings when >50% of the season-long N rate was already applied at planting. Therefore, this 2017 and 2018 Indiana-based field research addressed three questions i) are corn planters that deliver 50% to 100% of a full-season N rate at traditional or alternate band placements capable of matching or exceeding grain yields achieved by lower starter fertilizer N rates, ii) what is the impact of split N management on grain yield and/or N fertilizer recovery efficiency (NRE) when ≥50% of the total N rate is supplied at-plant, and iii) do alternate sidedress N placements (i.e. soil-surface streaming versus injection versus broadcast at multiple timings) in split-N sidedress applications influence grain yield and aboveground plant recovery of N fertilizer?<p></p> <p>To evaluate the consequences of moderate to high N rates banded at planting, urea-ammonium nitrate (UAN) was coulter-banded with a prototype Deere DB20 row-crop planter as close as 5cm x 5cm (5x5) (distance from soil surface x distance from seed row) to as far as 10x20 at planter applied N rates of 34, 101, and/or 202 kg ha-1. These at-plant applications were followed by a V5 to V6 stage mid-row sidedress application (if required) to achieve a uniform total N rate of 202 kg N ha-1. Analyses were primarily focused on 5x5 and 10x5 starter band positions as these were the only placements represented at the 34 kg N ha-1 rate. In these placement comparisons, 5x5 banding yielded similarly to 10x5 banding in 2017, but increased yield 6.6% (averaged across 34, 101, and 202 kg N ha-1 rates) in 2018. Corn grown in 2018 with at-plant rates of 101 and 202 kg N ha-1 produced grain yields statistically similar to or greater than that obtained with the 34 kg N ha-1 rate (averaged across 5x5 and 10x5 placements). In 2018, the 101 kg N ha-1 rate increased yields by 14.8% and NRE by 18.5 g g-1 compared to banding of 34 kg N ha-1. A secondary analysis included 6 placements (5x5, 5x13, 5x20, 10x5, 10x13, and 10x20) at just the 101 and 202 kg N ha-1 rates. Among these additional placement treatment combinations (averaged across 101 and 202 kg N ha-1 rates), both 5x13 and 10x20 banding reduced grain yield in 2018 by 12.5% and 10.1%, respectively, when compared to 5x5 banding. No yield differences among these 6 at-plant placements were found in 2017. Therefore, moderate to high N rates can be banded safely at-planting with the typically close starter fertilizer placements, but higher NRE and optimum yields can be achieved when a 50:50 split N fertilizer management approach is used.</p> <p>The optimal sidedress experiment targeted placement and/or timing impacts on corn yields and NRE when at-plant N was ≥50% and sidedress N was ≤50% of the total N rate. Single at-plant (AP) applications at total N rates of 26 (Zero), 112 (AP_112) and 224 (AP_224) kg N ha-1 were compared to split applications of 202 kg N ha-1 (with ~55% of total N applied at-plant plus the balance at sidedress). Sidedress N was applied at V5 or V12 timings with surface streamed versus subsurface injection of UAN, or via high-clearance broadcasting of urea at the V8-stage. In nearly every split sidedress approach, apart from the V12 injection treatment in 2017, grain yields and NRE with split-N sidedress responded similarly to AP_224 each year despite the reduced total N rate at 202 kg N ha-1. Both V12 streaming and AP_224 yielded 6.7% more than the V12 injection approach in 2017. The reduced yield in 2017 from late-season injection contributed to the 4.6% grain yield gain for surface-streaming applications (averaged across timings) with no apparent NRE advantage.</p> <p>These responses confirmed that in-season sidedress N placement influenced yield and, in our case, the surface-streaming advantage over injection was most evident at V12 where late vegetative to flowering rainfall was plentiful. Similarly, planter N placement was not influenced by N band depth as much as by N band distance from the seed row where 13 and 20cm distances occasionally decreased yield in 2018. This research provided evidence of modern placement technology impacts at planting and sidedress times where UAN placed near corn seeds in the seed-furrow and/or plants in the row never reduced, and occasionally increased, grain yield and/or N recovery in corn cropping systems.</p> <p> </p>

Master of Science / Department of Agronomy / David B. Mengel / Nitrogen fertilizers play an essential role in agricultural production in Kansas, particularly in row crops such as corn (Zea mays L.) and grain sorghum (Sorghum bicolor (L.) Moench). A good portion of the corn and grain sorghum grown in Kansas is typically grown using no-till production systems. These systems leave a large amount of surface residue on the soil surface, which can lead to ammonia volatilization losses from surface applied urea-containing fertilizers and immobilization of N fertilizers placed in contact with the residue. Leaching and denitrification can also be a problem on some soils. Current nitrogen prices, as well as concerns over environmental stewardship, are forcing producers to make smarter choices in the fertilizer products used as well as when and how the materials are applied, to optimize their nitrogen use efficiency. A common practice throughout Kansas is to apply N fertilizers prior to planting, sometimes up to 6 month prior to planting. What affect does this practice have on nitrogen availability to the growing crop? Current Kansas State University (KSU) soil test fertilizer recommendations assume 50% nitrogen use efficiency. This means of every pound of nitrogen applied only half will be utilized by the plant and turned into valuable grain. Possible solutions to help increase nitrogen use efficiency are the use of nitrogen additives which are currently on the market and claim to reduce nitrogen loss through denitrification and volatilization as well as the use of timing and application of fertilizers to further increase nitrogen use efficiency. The objective of this study is to evaluate different N fertilizer products, as well as additives and application practices and determine whether specific combinations can improve yield and N use efficiency of no-till corn and grain sorghum. The long-term goal of this study is to quantify some of these relationships to assist farmers in selecting specific combinations that could enhance yield and profitability. In this study five tools for preventing N loss were examined: fertilizer placement, or placing N below the soil surface or in bands on the residue-covered soil surface to reduce immobilization and/or volatilization; use of a urease inhibitor Agrotain (NBPT) that blocks the urease hydrolysis reaction that converts urea to ammonia and potentially could reduce ammonia volatilization; the use of a commercially available additive, Agrotain Plus, that contains both a nitrification inhibitor (DCD) and a urease inhibitor to slow both urea hydrolysis and the rate of ammonium conversion to nitrate and subsequent denitrification or leaching loss; use of a commercial product NutriSphere-N, which claims urease and nitrification inhibition; and the use of a polyurethane plastic-coated urea to delay release of urea fertilizer until the crop can use it. The ultimate goal of using these practices or products is to increase N uptake by the plant and enhance yield. An important measurement that was developed for this research was the use of a greenleaf firing index which used the number of green leaves below the ear at pollination as a key measurement in determining the effectiveness of fertilizer placement, application method, application timing and the use of nitrogen additives. If significant differences in lower leaf nitrogen stress are found, the potential exists to further develop this index and correlate differences observed with key parameters of nitrogen uptake such as ear-leaf nitrogen concentration, total nitrogen uptake and grain yield. Results observed from this research show that the potential to increase nitrogen use efficiency and reduce nitrogen loss do exist with the use of certain nitrogen additives, application methods and application timing. When conditions are conducive for nitrogen loss the use of currently available tools to protect nitrogen from volatilization, immobilization and/or denitrification loss significantly increased yields in the corn experiments. Results from the grain sorghum research indicate that when N losses limit yield, the use of products and practices enhance yield. In locations where nitrogen loss is minimal or low yields limit nitrogen response, the use of these practices was not found to be helpful.