R. B. Reneau

Soil solution Al as a measure of al toxicity to alfalfa in acid soils

Abstract The root system of alfalfa (Medicago sativa L.), known for extreme sensitivity to Al toxicity, has been observed to penetrate acid subsoil horizons high in exchangeable Al. In our previous studies we noted that root penetration into acid subsurface horizons occurred where lime had been surface applied under both no‐till and conventional tillage management systems. In order to more fully understand this seeming contradiction, the present study was undertaken. It was hypothesized that exchangeable Al may not be an adequate indicator of the activity of Al in solution and consequently the potential toxicity to the plant may be over estimated. To test this hypothesis, concentrations and activities of Al, Ca, and other major macro and micro elements and pH were determined in an Ernest silt loam (fine‐loamy, mixed, mesic Aquic Fragiudult) soil solution and compared with soil exchangeable levels. Soil samples were taken from the surface (0–5 cm) and 1 m depth in soils that had received 13 Mg/ha surface d...

Alfalfa seedling growth in nutrient solutions as influenced by Aluminum, Calcium, and pH

Abstract Soil acidity is a major factor responsible for reduced alfalfa (Medicago sativa L.) yields in humid regions of the United States. The purpose of this study was to investigate the effect of Ca, Al, and pH interactions on alfalfa growth. Two experiments were conducted in modified plastic growth pouches. Experiment 1 studied the influence of pH (4.5 and 6.5) at varying levels of Al (0.00, 0.08, 0.15 mM) with 1 mM Ca, while experiment 2 studied the interaction between Ca (0.00, 0.30, 1.00, 3.00, 6.00 mM) and Al (0.00, 0.08, 0.15, 0.30 mM) at pH 4.5 on alfalfa shoot and root development. In the absence of Al, root and shoot growth were not affected by a pH of 4.5 as compared to a pH of 6.5. Increasing Al from 0.00 to 0.30 mM caused a reduction in both shoot and root growth at pH 4.5 when Ca was less than 3.00 mM. In the presence of 0.08 mM Al, additional Ca at 3.00 and 6.00 mM increased shoot growth equal to that of the 0.00 Al treatment. The optimum level of Ca for root development was at least 1.00 ...

Corn yield and nitrogen uptake as influenced by tillage and applied nitrogen

Abstract No‐till management systems have been reported to reduce nonpoint source (NPS) pollution from agricultural fields. However, questions have been raised concerning the fate of nitrogen (N) in these systems. Increased moisture conservation and reduced runoff from no‐till systems have the potential to accelerate leaching of nitrate (NO3 ‐) out of the root zone, thus altering the problem from one of surface water degradation to one of ground water pollution. However, it is also probable that the additional moisture conserved in no‐till systems result in increased crop yield and N uptake. Time of N application and source of N could influence yield and N recovery and thus limit N losses during critical periods. A 3‐year study was conducted to determine if the fate of N applied to nonirrigated corn (Zea mays L.) would be influenced by tillage system, N rate, and time and source of N application. This paper addresses the impact of these practices on yield and N uptake. The experimental site was located on ...

Yield and elemental composition of wheat grain as influenced by source and rate of nitrogen

Abstract Application of sewage sludges to winter wheat (Triticum aestivum L.) is a possible mechanism to supply nutrients to the crop while simultaneously reducing the need for more expensive and less desirable disposal strategies. Research was conducted during 1986 and 1987 to determine the effect of fall applied sewage sludges on yield, N recovery, and elemental composition of wheat grain. The study was conducted in a corn (Zea mays L.)‐wheat‐soybean [Glycine max (L.) Merr.] rotation located on a Suffolk sandy loam soil (coarse, loamy, siliceous, thermic Typic Hapludult). The N treatments applied consisted of 0 (control), 30, 60, and 90 kg N ha‐1 from UAN solution applied in the spring and two anaerobically digested sewage sludges (one lime conditioned and the other lime stabilized) designed to supply 80 kg of plant available N ha‐1 applied in the fall. Twenty kg of N as UAN solution were applied in the fall when the wheat was seeded to all treatments except the control and the sewage sludge treatments....

Effect of sulfur on winter wheat grown in the coastal plain of Virginia

Abstract Limited information is available for the S requirements of higher yielding winter wheat (Triticum aestivum L.) crops grown in the eastern United States. Three experiments were conducted in the Coastal Plain region of Virginia on Kenansville loamy sand (loamy, siliceous, thermic Arenic Hapludult), Dothan loamy sand (fine‐loamy, siliceous, thermic Plinthic Paleudult), and Pactolus loamy sand (thermic, coated Aquic Quartzipsamment) soils. These three soils have low monocalcium phosphate‐acetic acid extractable SO4‐S (<3.1 kg/ha) and would be expected to be S deficient With respect to corn (Zea mays L). Winter wheat response to S application was investigated on the Kenansville and Dothan soils, while the N x S interaction was studied on the Pactolus soil. In the two studies where S was the dependent variable there was no significant change in concentration of the flag leaf at Feekes growth stage 10 for N, S, P, K, Ca, Mg, and N/S ratio. Also yields were not significantly influenced by S application a...

Foliar diagnostic norms for sorghum

Abstract The Diagnosis and Recommendation Integrated System, previously applied successfully to many other crops, is shown to be an appropriate foliar diagnostic tool for sorghum (Sorghum bicolor L.) with respect to N, P, K, Ca and Mg. The norms were developed from a data bank comprising 907 observations of tissue composition and yield gathered from the literature and investigators’ files. The total population of observations is divided into a high and low subpopulation on the basis of yield. Those forms of expressing tissue composition which discriminate best between the two subpopulations are used to compute DRIS indices which measure the extent of the deviation from the established norm. An independent set of data from two field experiments is used to show that the norms can validly diagnose nutrient insufficiences which when, corrected result, in yield increases.

On‐Site Waste Treatment and Disposal by Sequencing Batch Reactor‐Drip Irrigation: Effluent Distribution and Solute Transport

Abstract On‐site wastewater systems (OWS) are used in areas not served by municipal treatment systems for biological and chemical renovation of wastewater prior to its entrance into surface or groundwaters. A traditional OWS (septic‐tank effluent with gravity dispersal) may not function properly in soils with low hydraulic conductivity horizons or other restrictive features. Uniform dispersal of highly treated effluent (HTE) in conjunction with controlled dosing offered by subsurface drip irrigation systems (SDIS) can play an important role in overcoming these limitations. An OWS consisting of a sequential batch reactor (SBR) for production of HTE and a SDIS to control dosing and dispersal of the SBR effluent (SBRE) was used in this study. The OWS is designed to treat 18,925 L of SBRE d−1. Efficiency of wastewater treatment by the OWS was evaluated by analyzing the SBRE and soil solution collected beneath the SDIS for several water‐quality parameters. Measuring soil‐water potentials monitored the effectiveness of the SDIS to disperse effluent. The SBR produced HTE with fecal coliform counts averaging less than 4,000 CFU 100 mL−1, and more than 95% of the N was present as nitrate. Soil‐water potentials ranged between −5.1 and −56.5 KPa beneath the SDIS. None of the soil solution samples was positive for fecal coliforms. Nitrate concentration in soil solution was lower beneath the SDIS than in the SBRE. This decrease was attributed to plant uptake and denitrification. Phosphorus (P) concentration was reduced by 99% beneath the SDIS when compared with P concentration present in the SBRE.

Effect of subsurface acidity on alfalfa in a Tatum clay loam

Abstract Soil acidity is a major cause of low yields and reduced longevity of alfalfa (Medicago sativa L.) in the Eastern United States. This research was conducted to investigate the effectiveness of subsurface placement (30 cm) of P and K fertilizer and dolomitic lime on alfalfa yield and quality. The study was carried out in 1981 and 1982 on a Tatum clay loam (Typic Hapludult, clayey, mixed, thermic) soil where plowsole amendments were applied in 1980. The experimental design was a completely randomized block and was seeded with ‘WL 311’ alfalfa. Yields and root length were not altered by the absence of plowsole application of lime, P or K. Soil exchangeable Al was higher, while pH was lower for soils in the control, as compared to treatments where lime was placed in the plowsole. These data indicate that the ‘WL 311’ variety will grow through the Tatum soil subsurface horizons in spite of its acidic nature and high exchangeable Al content. This may be related to the greater tolerance of this variety t...

Alfalfa yields and quality as influenced by subsurface application of phosphorus, potassium and limestone

Soil acidity is a major growth limiting factor for alfalfa (Medicago sativa L.) production in the United States. Subsurface soil acidity has been shown to limit alfalfa root systems resulting in reduced moisture and nutrient uptake. This research was conducted to investigate the effectiveness of subsurface placement (30 cm) of P, K, and dolomitic limestone on alfalfa yield and quality. Subsurface amendments were applied to a Davidson clay loam (clayey, kaolinitic, thermic, Rhodic Paluedult) soil in Dec. 1979. In addition the study received a surface application of dolomite in 1980. The experimental design was a randomized complete block design with 4 replications and was seeded to ‘WL 311’ alfalfa in 1982. Limestone, P and K treatments had no effect on yields of alfalfa between 1983 and 1985, however subsurface limestone and P increased yields in 1986 and 1988. Alfalfa quality was increased in 1988 with plowsole lime and P. In 1988 tissue N and total N uptake was higher on subsurface lime-amended plots, however other elements were unaffected by plowsole lime, suggesting N fixation to be a limiting factor for alfalfa growth on acid soils. Soil pH in the 0–15 cm depth averaged 6.9 from 1982–1985 and decreased to 6.5 in 1988. Addition of plowsole lime increased soil pH in the plowlayer from 6.1 to 7.0, however lime had no effect on Al and Mn levels. Calcium and Mg were also increased in the plowlayer from subsurface lime application. This study indicated plowsole lime and P increased yields and quality of alfalfa when the surface soil becomes acidic, however when the surface soil is limed there appears to be no advantage from subsoil amendment of lime, P and K.

Corn forage yield and chemical composition as influenced by sulfur fertilization

Abstract Soil sulfur (S) deficiency for plant growth has become an increasing problem in the United States. A field experiment was conducted to investigate effects of fertilization with 0 and 67 kg S/ha as a single or split application, in a Latin square design, on corn (Zea mays L.) forage yield and chemical composition. Sulfur fertilization by either method increased yield of whole plant and grain 7% and increased number of plants with two ears. Total S and sulfate‐S concentration in whole corn plants, leaf, stem, and grain were increased with S fertilization. The nitrogen (N):SO4‐S ratio was a useful indicator of S deficiency.