Land disposal of beef-feedlot manure was studied. Annually, beginning in the fall of 1969, feedlot waste was applied to a silty clay loam soil at rates that after 4 years ranged from 114 to 2,750 metric tons/ha of dry manure. Included were three single applications made in the fall of 1969 (residual) that ranged from 123 to 590 dry metric tons/ha. For 3 years, in the spring and fall, surface soil samples and soil cores were taken. Yields of furrow-irrigated corn (Zea mays L.) forage and plant contents of N, P, K, Ca, Wig, and Na were measured.Chemical composition of manure from a single feedlot varied greatly. Average composition (dry weight basis) of samples collected for 3 years was 20.5% H 2 O, 0.92% N, 0.52% P, 1.14% K, 0.92% Ca, 0.41% Mg, and 0.26% Na. At all sampling dates electrical conductivities (EC) of extracts from saturated pastes of the surface soil samples from plots receiving yearly manure treatments were linearly related to cumulative tons of applied manure; EC values of more than 10 mmho/cm were recorded for the spring samplings. Both yearly and residual manure treatments caused Na and NO 3 -N to move downward accumulating to depths of at least 1 m after 3 years; movement of K and P was restricted to 50 and 30 cm, respectively. Corn-forage yields were increased by improved soil fertility at the low and intermediate yearly rates, but depressed at the high rates, probably because of salt injury. After 4 years forage yields were still increased on plots that received residual treatments. Uptake of N and P was also depressed at high yearly rates and followed trends similar to those of yield 1 Yearly rates ranging from 29 to 68 dry metric tons ha~* year" 1 produced near maximum forage yields without causing excessive salt accumulation in the soil.Additional Index Words: nutrient uptake. animal waste, nitrate, soil salinity.
Simulation models are useful in observing and understanding the interrelationships among soil water supply, drainage, evapotranspiration (ET), and crop yield. The objective of this study was to develop a water balance model and then a microcomputer software package for illustration of drainage, ET, and crop yield as influenced by water conditions. A model was developed that estimates drainage by using a Wilcox-type drainage equation, crop ET by using the Jensen-Haise reference ET equation, and crop yield from yield-ET functions. Weather records and field research results from Tribune, KS, were used for adaptation of the model to western Kansas. Based on this model, a Windows compatible microcomputer software package (KS Water Budget v. TI) was developed for corn (Zea mays L.), grain sorghum [Sorghum bicolor (L.) Moench], sunflower (Helianthus annuus L.), and winter wheat (Triticum aestivum L.). The software allows users to study the effects of irrigation system efficiency, water application timing and amount, and water conservation under dryland conditions. Daily crop ET, drainage, and available soil water are illustrated in graph form. Estimated drainage, ET, and seed yield are presented in a summary table. The software is to be used as an educational tool for illustration of water's influence on crop production in the region of western Kansas-eastern Colorado with a deep silt loam soil developed from loess.
A two-year study was initiated in the spring of 1990 on a Keith silt loam soil (Aridic Argiustoll) in northwest Kansas to determine if irrigation scheduling with planned soil water depletion could be used successfully for irrigated corn fZea mays L.) as a method of conserving and protecting groundwater resources without reducing yields. The study was conducted using surface irrigation in small dead-level basins. Planned soil water depletion was attempted by allowing a small additional daily deficit (0, 1, or 2 mm/day) to accumulate in irrigation amounts as scheduled by an evapotranspiration (ET)-based water budget. The daily deficit amounts were imposed on three irrigation levels, heavy (1.25 X ET), normal (1.00 x ET), and deficit (0.75 x ET) which represented a range of management by irrigators. The plant-available soil water at physiological maturity was related linearly to irrigation amounts. However, the plantavailable soil water at physiological maturity was reduced by only 25 mm for each 100 mm reduction in irrigation. Imposition of a small daily deficit of 1 mm/day after tasseling resulted in yield reductions of 7,1, and 3% for the heavy, normal, and deficit irrigation management levels, respectively. The 1 mm/day deficit resulted in irrigation savings of approximately 12, 9, and 0% for the three respective irrigation management levels and generally resulted in slight reductions in available soil water at physiological maturity. In some cases, the imposition of the 1 mm/day deficit had little eftect on the total seasonal irrigation amount, but simply shifted the irrigation event to a later date. The larger 2 mm/day daily deficit after tasseling reduced yields by 7, 9, and 15% for the three respective irrigation levels and reduced irrigation amounts by 19, 26, and 25%. Yields were related linearly to irrigation and water use with a reduction in irrigation or water use reflected by yield reductions. Water use efficiencies were similar whether planned soil water depletion was used or not. Therefore, from a water conservation standpoint, irrigation scheduling with planned soil water depletion was not justified. Keywords, Irrigation, Soil water depletion. Corn, Water use efticiency. D eclining groundwater supplies, increased competition for available water resources, and irrigation-induced, water-quality problems have resulted in an increased need for waterconserving irrigation practices. Irrigation practices for com production in western Kansas usually extend watering until late in the season, resulting in high levels of soil water remaining in the profile in the fall after harvest. Rogers and Lamm (1994) found in a survey of 82 producer fields in northwest Kansas that plant-available soil water contents after com harvest averaged 70% of field capacity for a 1.5-m-depth soil profile. One method of conserving water would be to mine the plant-available soil water gradually during the irrigation season, in anticipation of recharge from precipitation during the off season. This concept of irrigation scheduling
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