Hubert J. Savoy

Assessment of plant biomass and nitrogen nutrition with plant height in early-to mid-season corn

BACKGROUND The physiological basis for using non-destructive high-resolution measurements of plant height through plant height sensing to guide variable-rate nitrogen (N) applications on corn (Zea mays L.) during early (six-leaf growth stage, V6) to mid (V12) season is largely unknown. This study was conducted to assess the relationships of plant biomass and leaf N with plant height in early- to mid-season corn under six different N rate treatments. RESULTS Corn plant biomass was significantly and positively related to plant height under an exponential model when both were measured at V6. This relationship explained 62-78% of the variations in corn biomass production. Leaf N concentration was, in general, significantly and positively related to plant height when both were measured at V6, V8, V10 and V12. This relationship became stronger as the growing season progressed from V6 to V12. The relationship of leaf N with plant height in early- to mid-season corn was affected by initial soil N fertility and abnormal weather conditions. CONCLUSION The relationship of leaf N concentration with plant height may provide a physiological basis for using plant height sensing to guide variable-rate N applications on corn.

Irrigation, Fertigation, and Plasticulture Increase Yield and Quality while Reducing Carcinogen Formation in Burley Tobacco

U.S. tobacco growers are competing in a recently deregulated market with greater supply coming from abroad and shrinking U.S. demand for their product. Tobacco production based on preplant fertilization and reliance on natural precipitation has become less profitable under current conditions. This study tests the benefit of irrigation, fertigation, and plasticulture to produce higher tobacco yield and quality while reducing carcinogens, tobacco specific nitrosamines (TSNA). Burley tobacco (TN 90) was grown at Greeneville, Tennessee (Lindside silt loam) and Springfield, Tennessee (Dickson silt loam) during the years 2005-2007. In one set of treatments, drip irrigation supplemented rainfall to supply at least 2.54 cm/wk in order to maintain soil tension at more optimal levels. Fertigation also used supplemental irrigation but applied nitrogen fertilizer in four split applications intended to better match the plants demand for nitrogen. Plasticulture used the same fertigation protocol but added a plastic mulch covering to isolate the benefits that could be obtained from increasing soil temperature. Finally, all these production practices were tested at recommended and reduced nitrogen rates, 224 to 112 kg N/ha.

Effects of optical sensing based variable rate nitrogen management on yields, nitrogen use and profitability for cotton

This research evaluated the profitability and nitrogen (N) efficiency of real time on-the-go optical sensing measurements (OPM) for variable-rate (VRT) N management for cotton. Two forms of OPM-based VRT N management and the existing farmer practice (FP) were used to determine N rates applied to cotton on 21 farm fields in the lower Mississippi River Basin states of Louisiana, Mississippi, Missouri and Tennessee, USA. A modified version of the Schabenberger and Pierce on-farm experimentation model was used to evaluate VRT N management and landscape, soil and weather factors on lint yields, N rates, N efficiency (lint yield divided by N rate) and net returns. Field level mean lint yields were not different between VRT and FP. VRT decreased N rates applied on four fields and increased N rates applied on four other fields. However, landscape, soil and weather attributes specific to fields influenced VRT N rates. VRT N rates were similar to FP N rates on the other fields in the study. N efficiency was not improved with VRT N management. N rates were not low enough to increase N efficiency. Changes in lint yields and N rates due to VRT coupled with USDA NRCS Environmental Quality Incentive Program cost-share payments were not sufficient to produce higher net returns relative to FP N management at the field level. In this multi-site, multi-year study, yields and net returns from VRT were not different from FPs which did not utilize variable rate N management.

Changes of Soil Microbial Population and Structure Under Short-term Application of an Organically Enhanced Nitrogen Fertilizer

Abstract Interest in the use of alternate fertilizers has increased during recent years to improve soil productivity. An organically enhanced N fertilizer, containing 14.9% N, 4.3% P2O5, 18.1% S, 0.6% Fe, and 8% organic C, and is produced from a sterilized organic additive extracted from municipal wastewater biosolids and chemical fertilizers was evaluated for its effects on soil microbial populations and abundances in 0- to 15-cm depth of of two silt loam soils located at Jackson and Grand Junction, Tennessee. This treatment was compared to conventional N fertilizers and zero N control under nonirrigated corn (Zea mays L.) from 2011 to 2013. Three N-applied treatments (organically enhanced N fertilizer, ammonium sulfate, urea/NPKZn briquette) at 128/170 kg ha−1 and the zero N control were imposed at each location. The organically enhanced N fertilizer decreased the relative abundance of arbuscular mycorrhizal fungi but increased that of general microbes relative to the zero N control and increased that of general microbes compared with NPKZn briquette 4 to 7 months after their applications at an N rate of 128 kg ha−1 for corn within 2 years of experimentation on a relatively infertile soil with low organic matter. Soil general microbes and arbuscular mycorrhizal fungi were the two sensitive indicators of soil microbial structure response to fertilization. However, effects of the organically enhanced N fertilizer on soil microbial populations were not noticeable after corn harvest. In conclusion, application of the organically enhanced N fertilizer has noticeable influence on soil microbial structure/abundance but not on populations on relatively infertile soils with low organic matter from a short-term perspective.

Evaluation of Sulfur Fertilization Effects on Yield, Quality, and Nutrient Content of Bermudagrass Hay

Yield, quality, and nutrient content of Vaughn’s #1 Bermudagrass® as affected by sulfur (S) fertilization was evaluated in a 2-year field study. The study area was initially established in July 2004. Soil type was a Staser silt loam (fine-silty, mixed, thermic Cumulic Hapludoll) well drained, dark brown, and cherty with 0 to 2% slope. Sulfur rates of 22.4 and 44.8 kg S−1 ha did not significantly (P < 0.05) affect yield of Vaughn’s bermudagrass in the 2 years of observations. Copper levels showed a highly significant response to S applications (P < 0.01). As S increased, the concentration of copper in the plant decreased. Nitrogen (N) as nitrate (NO3) levels in the harvested forage were elevated among treatments in 2006; however, no significant difference was found in 2007. The greatest mean nitrate concentration in a single harvest was 1225 mg kg−1 N-NO3 on September 2006, which is safe to feed to cattle.

Growing Season Measurement of Petiole Sap Nitrate-N Concentrations in Burley Tobacco to Predict Yield and Tobacco Specific Nitrosamines in the Cured Leaf

Nitrogen is one of the most important inputs over which Burley growers have control. Nitrates accumulate in the leaf and form building blocks for bacteria that create tobacco-specific nitrosamines (TSNAs). Tobacco-specific nitrosamines are important to buyers because they constitute some of the most potent carcinogens in tobacco. During the course of a two-site, 3-year Burley tobacco-growing practices study, the Horiba Cardy meter readings of nitrate-nitrogen (N) in petiole sap were evaluated for predicting both yield and TSNAs from petiole sap nitrate-N analysis. Yield results did not correlate well with petiole sap nitrate-N at 6 weeks after harvest. Yield response to applied nitrogen was much less than expected and in some cases lacking at all and this probably accounts for the poor correlation observed. Correlation of petiole sap nitrate-N at week 8 from transplant and TSNA concentrations in the cured leaf were consistent and ranged from 0.39 to 0.86.

Should Tennessee Tobacco Growers Invest in Irrigation, Fertigation or Plastic Mulch? (An Extension Fact-Sheet based on recent research)

U.S. tobacco growers are competing in a recently deregulated market with greater supply coming from abroad and shrinking U.S. demand for their product. Tobacco production based on preplant fertilization and reliance on natural precipitation has become less profitable under current conditions. This fact sheet combines the results of two studies that tested the benefit of irrigation, fertigation, and plasticulture to produce higher tobacco yield and quality while reducing carcinogens, tobacco specific nitrosamines (TSNA). Eight years of study and two sites formed the basis for tobacco irrigation recommendations that were representative of Tennessee conditions.

A Study of Irrigation, Fertigation and Plasticulture in Burley Tobacco Production with a Focus on Yield, GRI and TSNA Concentration

. A three-year, two site study was used to evaluate the benefits in yield, quality and tobacco specific nitrosamines (TSNA) reduction obtained from drip irrigation of burley (TN 90) tobacco. The sites were located at Greeneville, TN (Lindside silt loam) and Springfield, TN (Dickson silt loam) during the years 2005 – 2007. Within this three year span, precipitation was near ideal in one crop season (2006 Greeneville), and very dry in another (Springfield 2007), with 2005 being about average for each site. While an ‘average’ precipitation season is considered sufficient in volume to meet plant water demand, irrigation displayed the potential to increase yields during dry years, as well as address the importance of precipitation timing during critical growth stages to attain high quality low TSNA leaf during average precipitation years. Drip irrigation was evaluated using three protocols. The first used irrigation to supplement precipitation to achieve a minimum of 1 inch of water applied per week. The second followed the same irrigation protocol, but used drip-tape to make split liquid urea fertigation applications. The third treatment used the same fertigation protocol, but included the use of a plastic mulch. Each protocol included a reduced nitrogen (N) rate to determine if optimized soil moisture increased plant nutrient uptake and utilization efficiency.