Preliminary studies revealed that exchangeable K levels in Iowa soils fluctuated in response to vapor pressure changes and air drying. This phenomenon was investigated in relation to (1) K nutrition of plants in the greenhouse and (2) the problem of predicting the relative K‐fertility status in a wide range of Iowa soils. The thirteen soils employed in the greenhouse study showed variable increases in exchangeable K content upon air drying. Accompanying increases occurred in K uptake by the corn plants. Effects on K absorption by plants associated with drying of the soils often were equivalent to applying 60 to 120 lbs. K per 2 million lbs. of soil. Relative ability of the soils to supply K to plants under green‐house conditions was better correlated with exchangeable K content of undried than of air dried soils. This was true whether or not soils were air dried for cropping. Under field conditions, fluctuations in soil moisture levels in the surface one‐inch layer were accompanied by marked changes in content of exchangeable K over an 11‐week period. Below this layer, exchangeable K remained nearly constant since moisture content did not drop so low as in the surface. Results obtained in both field and laboratory showed that not much increase in exchangeable K occurred until soil moisture level had dropped to near 5 per cent or below. On the basis of overall results obtained it is concluded that for Iowa soils exchangeable K values determined after air drying may not be as reliable as those determined on moist soils, in predicting K supplying abilities of soils. Additional field studies are needed, however, to evaluate effects of alternate drying and wetting of soil on K nutrition of the crop.
A dairy cow population of 143,000 in an area of 150 km2 enriched the atmosphere with distillable N (mostly NH3) over an area in excess of 560 km2. Over an area of 35 km2, where cow population density was approximately 1,600 cows/km2, the concentration of distillable N in the atmosphere was between 20 to 30 times greater than at a control site outside the dairy area. Highest concentrations of N were associated with wet corral surfaces and favorable evaporative conditions. Approximately 20% of the total N absorbed by acid‐surface traps in the dairy area was nondistillable N while filtered air samples contained 5% or less. Rainfall delivered three times as much N to the land surface inside than outside the dairy area.
Simultaneous 24‐hour air sampling, 0.8 km upwind from the nearest cows in a large dairy area (145,000 cows) and 11.2 km upwind from the dairy area, showed distillable N (mostly NH3) concentrations of 190 and 6 µg/m3, respectively. An average distillable‐N concentration of 540 µg/m3 was measured during a 24‐hour sampling at the downwind corral fence of an isolated 600‐cow dairy. These data indicate significant N loss from dairy waste by NH3 volatilization. The significance of the effects of these higher atmospheric concentrations on NH3 absorption by soils, surface waters, and crops remains to be fully evaluated. Meteorological factors, particularly temperature inversions in the atmosphere and wind, along with proximity to the waste, greatly affected atmospheric concentrations of distillable N. A marked diurnal fluctuation with low concentrations in the afternoon and high concentrations at night were frequently recorded in the large dairy area. Higher nighttime values were related to temperature inversions in the atmosphere. A reversed diurnal pattern with the high afternoon and low nighttime concentrations were recorded at the isolated‐dairy site. Close proximity to the source and a high horizontal flux of distillable N with afternoon winds were important factors in this diurnal pattern. Winds averaging 9.3 km/hour transported distillable N 500 m from the isolated dairy at a height of 1.2 m.
Resin coatings are very effective in controlling the availability of N from applied urea in moist soil. In leaching studies, 94% of the noncoated urea was recovered in 1 day, compared to a 49% recovery of the N from coated urea (13.2% resin) in 4 weeks of intermittent leaching.Release rates are controlled by the thickness of the coating and the temperature of the medium. Coatings averaging 13.2% resin markedly decreased release of urea, compared to coatings of 9.0% resin. In the range beween 5 to 35C, increased release of urea accompanied increases in temperature. After 4 weeks of incubation and intermittent leaching totaling 20 inches of water, 25 and 67% of the added N were leached from soil at 5 and 35C, respectively. Increasing the temperature 10C was approximately equivalent to doubling the release time within a 16-week period. Increasing the temperature increases expansion of the capsule and the surface area through which diffusion must take place. This effect is probably supplemental to the effect of temperature on the diffusion phenomena per se. Approximately 99% of the capsules were recovered intact after incubation for 16 weeks at four temperatures between 5 and 35C.
Synopsis Yields of irrigated safflower decreased between 150 and 300 pounds per acre for each 4‐ to 6‐week delay in planting from January 16 to April 23. Seed weight, hull content, linoleic acid content, and iodine values of the oil decreased in the later plantings, while oil content of seed increased. Total irrigation requirements for January, February, and March plantings were similar. Average consumptive moisture use was 34.4 inches, and the peak average daily moisture use was 0.39 inch.
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