Browsing by Author "Menelik, G."

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    Effects of tillage and nitrogen fertilization on nitrogen losses from soils used for corn production
    Menelik, G.; Reneau, Raymond B.; Martens, David C.; Simpson, Thomas W.; Hawkins, George W. (Virginia Water Resources Research Center, Virginia Polytechnic Institute and State University, 1990-12)
    Research was conducted in soils of the Chesapeake Bay area to determine the effects of tillage practice and nitrogen (N) fertilizer application rates on N leaching from corn fields. Three well known computer models (NTRM, CERES-Maize, and VT-MAIZE) were tested to determine their ability to predict the distribution of N in (a) soil and crop, (b) the components of the N cycle, and (c) corn yields. To accomplish the above objectives, two field sites were selected on agronomically important soils for either a corn (Zea mays L.)-wheat (Triticum aestivum L.)-soybean (Glycine max [L.] Merr.) or a continuouscorn rotation. The corn-wheat-soybean rotation was located on a Suffolk sandy loam soil (coarse loamy, siliceous, thermic Typic Hapludult) in the immediate Chesapeake Bay drainage basin. The continuous-corn rotation was located on a Groseclose silt loam soil (clayey, mixed, mesic Typic Hapludult) typical of finer-textured soils located in the upper reaches of tributaries that drain into the Chesapeake Bay. Management practices evaluated included tillage system and rate, source, and time of N application. Specifically, we looked at conventional vs. no-till; inorganic N vs. sewage sludge; preplant vs. split application of N; and a variety of N application rates. The N treatments for corn were 0, 75, 150, and 225 kg N ha-1 applied preplant; 150 kg N ha-1 applied 4 weeks after emergence; and 150 kg of mineralizable N ha-1 from anaerobically digested and either lime- or polymer-conditioned sewage sludge. The N treatments for wheat were 20 kg N ha-1 applied in the fall and 30, 60, or 90 kg N ha-1 applied in the spring; 60 kg N ha-1 split application; and 80 kg of mineralizable N ha-1 applied in the fall from either lime- or polymer-conditioned sewage sludge. In the Groseclose soil, there was an increase in total yield and N uptake when sewage sludge was applied compared to the split and preplant application of inorganic N. There was no difference between polymer-or lime-conditioned sewage sludge application. Also, there were no differences between preplant and split application of N. Where no-till was used, there was an increase in both yield and N uptake compared with conventional till. In the Suffolk soil, tillage management did not influence yield or N uptake where time and source of N application were studied. This lack of response on the Suffolk soil is attributed to severe moisture deficits that were present during the growing season on this coarse-textured soil. Nitrogen losses from the soil profile were directly related to the quantity of N remaining in the upper 1 m of the soil profile after the crop was harvested. Larger quantities of N were lost from the Groseclose soil where conventional till was employed during the first year of the study. This was attributed to enhanced mineralization where no-till was converted to conventional till and to lower yields and lower N recovery with conventional till. Losses of N tended to be higher from the conventional till plots because of the larger quantities remaining at the end of the growing season. It should be noted that the years during which these xvii studies were conducted were extremely dry, and the in the Groseclose soil where no-till management was employed resulted in increased yield and increased N recovery. This study also emphasizes the need for better methods for making N recommendations for crop production. The model performances varied from year to year and from one tillage practice to another. Because they were written for average soil and climatic conditions, they did not make satisfactory predictions in many instances. Such models require adjustment to reflect the moisture stress conditions that often prevail in this region for corn production.
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    Leaching and denitrification losses of nitrogen from corn fields as influenced by conventional- and no-till practices in soils of the Chesapeake Bay area
    Menelik, G. (Virginia Tech, 1990)
    Research was conducted in soils of the Chesapeake Bay area primarily to determine the combined effects of tillage practice and N fertilizer application rates on N leaching and denitrification losses from corn fields. Three well known models - the NTRM, CERES- Maize, and VT-MAIZE - were also tested to determine their predictive ability of N distribution in soil and crop, the various components of the N cycle, and corn yields. To accomplish the above objectives, two field sites were located (in 1986) for a 3 year study on agronomically important and representative soils that are used for corn production in the Chesapeake Bay drainage basin. The main plot treatment was tillage and consisted of no-till and conventional-till. The subplot treatments were N application rates which consisted of 6 levels with 4 inorganic and 2 organic (sewage sludge) N fertilizers. Denitrification experiments were also conducted on the Groseclose silt loam soil to estimate and compare N loss through denitrification from both till and no-till practices. C₂H₂ was used to inhibit N₂ production and N₂O was collected in closed chambers located on the soil surface. Tensiometers and neutron moisture meter access tubes were also installed to monitor soil moisture and energy levels. Nitrogen leaching losses were determined by applying the principle of N mass balance. Denitrification N loss during the corn growing season was less than 2% of the applied N fertilizer. The N losses from the two tillage systems were not significant at p > 0.10. If Fick’s law is to be applied for predicting N loss from the soil subsequent to C₂H₂ application, sampling must occur after a minimum preset critical time. In the Groseclose soil, there was an increase in both total yield and total N uptake when sewage sludge was applied compared to the split and preplant inorganic fertilizers applied at the same rate. There was no difference in yield or N uptake due to applying N as either preplant or a split application. Where no-till management was used, there was an increase in both yield and N uptake as compared with conventional tillage. In the Suffolk soil, tillage management did not influence yield or N uptake where time and source of N application were studied. The relationship between yield and N application rates for both soil types could be described with quadratic equations. The total N recovery could also be described with quadratic equations. However, these relationships do not hold every year for every season or tillage management practice. The no-till plots retained higher moisture content than conventional tillage plots in the upper 0-100 cm depth. Below 100 cm depth, however, no-till retained less than conventional till. The gain and loss of N in soil was dependent on the tillage type and seasons of the year. During the growing season, generally the conventional tillage gained more N than the no-till. During winter, however, the N losses due to leaching were proportional to the amount of N retained at the end of the growing season. Thus, conventional tillage lost more N by leaching during the winter months. Mineralization of N was higher in conventional till, while denitrification was higher in no-till. Split application has shown less N loss due to leaching than the preplant. Mineralization, denitrification, and leaching took place from both the upper and lower zones of the soil profile. The model performances varied from year to year and from one tillage practice to another. Since they were generally written for average (normal) soil and climatic conditions, they did not make satisfactory predictions under the severe moisture conditions experienced during this study. Thus, they require a great deal of readjustment. Considering all aspects, however, the NTRM is the best model. The unmodified VT-MAIZE is the next best.