Synopsis Potassium applications increased yield of seed cotton, size of bolls, and fiber micronaire values, but decreased lint percentage. K content of plants increased in proportion to rate of K applied. Old leaves plus perioles gave the best indication of the K status of the plant. Fiber quality was best at lower rates of K.
Synopsis Effective rooting depth decreased as soil moisture level increased. A high percentage of the roots was found in the surface 12 inches of soil for all species regardless of soil moisture level. Soil moisture extraction was used with reasonable accuracy to estimate effective rooting depth.
A linear form of the Freundlich isotherm was used to describe arsenite [As(III)] sorption by the A and B horizons of five West Virginia soils. Arsenite sorption conformed to the Freundlich isotherm over the entire concentration range for all the soils. Simple correlation coefficients and multiple regression equations were used to relate soil properties to parameters of the Freundlich equation. Iron oxide percentage and pH were the soil properties most closely related to parameters of As(III) sorption. The rate of As(III) sorption by the A and B horizons of an Upshur soil was rapid initially and decreased with time. A modified form of the Freundlich equation was used to explain the As(III) sorption rate data. Arsenite sorption was not reversible; only a small amount of the sorbed As(III) was released after five desorption steps. The modified Freundlich equation was also used to describe As(III) desorption rate. Simple and multiple regression calculations indicated that iron oxides and pH were correlated with the rate of As(III) desorption by the investigated soils.
The influence of tillage methods on the utilization of N from soil and fertilizer sources by crops has not been investigated previously by tracer methods to any great extent. The objectives of this study were to compare yields and N utilization of silage corn (Zea mays L.) in conventional and no‐till culture, using a double‐cropping system of corn and smooth bromegrass (Bromus inermis Leyss.). The experiment was initiated in 1974 on a Wharton‐Cookport (Aquic Hapludults‐Aquic Fragiudults) silt loam soil with an established stand of smooth bromegrass in West Virginia. Labeled (15N‐depleted) ammonium sulfate was surface‐applied annually at rates of 85, 170, and 340 kg N/ha over a 4‐year period. Herbicides (2.2 kg/ha atrazine; 1.1 kg/ha paraquat) were applied annually to the grassed and plowed plots to suppress the grass sod but allow bromegrass to resume growth after corn silage was harvested. The grass was not harvested for hay, but left as a cover crop for erosion control. Yields of corn plants were determined at midseason (11 to 12 leaf stage) and at the silage stage. The proportions of total N uptake contributed by the soil and fertilizer were determined by mass spectrometry. In 1974 and 1977 when soil water regimes were most favorable, total dry matter (TDM) yields were similar under the two systems of tillage, but in the intervening years of subnormal rainfall, yields were substantially higher from no‐till than from plowed plots. Amounts of available water in the surface 30 cm of soil were consistently higher in no‐till than in tilled plots during the growing season, but differences were not discernible in the underlying 30 an layer. The 4‐year average yields of silage TDM for all N rates were 13,400 and 11,570 kg/ha, respectively, for no tillage and conventional tillage. Because of the lower attainable yields on plowed plots in 1975 and 1976, the corresponding average amount of applied N required for near‐maximum yield under conventional tillage was about one‐half that required for no‐tillage. Soil N uptake tended to decrease with increasing rate of N applied, generally was unaffected by method of tillage, and differences among years were relatively small. For both samplings and all N rates in 1975 and 1976, uptake and recovery of fertilizer N were substantially higher under no‐tillage than under conventional tillage. In 1974 and 1977, enhanced recovery under no‐tillage was evident only at the highest N rate. Four‐year midseason recoveries from 85, 170, and 340 kg N/ha, respectively, were 42, 32, and 26% for no‐till and 35, 27 and 16% for conventional tillage. Corresponding average annual recoveries at silage harvest were 46, 53, and 46% for no‐till, and 53, 55, and 347, for conventional tillage.
An experiment was conducted under field conditions to study the movement and recovery of N15‐enriched nitrogen fertilizer added to soil in the forms of NaNO3 and (NH4)2SO4. The plots consisted of the soil mass inside cylinders 30 or 60 cm in diameter, which were pressed into the soil to a depth of 45–60 cm. These plots were either seeded to sudangrass (sorghum sudanense) or left uncropped. The plant tops, roots, and the soil, by 15‐cm layers, were analyzed for total N and excess N15 content. Recovery of added N15 from the 32 plots ranged between 96.3 and 101.8%, and averaged 99.0%. There was no significant difference in recovery of the fertilizer N due to the percent of excess N15 in the fertilizer, size of plot, exposure to natural rainfall, cropping, N source, or the time of application of the fertilizer. Wide variation in recovery of excess N15 occurred with core sampling and it was found necessary to remove, weigh, mix and subsample the entire soil mass from within the rims. The small amounts of unrecovered N were probably due to procedural errors in the field and laboratory, and leaching and root growth beyond the sampling zone. There was no indication of any N loss in the gaseous form. The fate of applied fertilizer N was followed under field conditions using N15‐enriched nitrogen fertilizer applied to the soil in situ enclosed by large steel cylinders. Total recovery of the fertilizer N from these experiments after 8 weeks ranged from 88 to 96%, but dropped as low as 77% after 10 months. Recovery of the fertilizer N was greater from an ammonium source than from nitrate. Retter recovery of fertilizer was obtained when the plots were cropped to sudangrass rather than left fallow. Doubling the rate of application of the fertilizer N from 336 to 672 kg/ha did not affect percent of total recovery. The 4 to 12% of fertilizer N unrecovered after 8 weeks appears to be due to a loss in the gaseous form, since special precautions were taken to restrict leaching and to eliminate errors in sampling and analysis.
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