Arthur B. Onken

Use of the nitrate electrode for determination of nitrates in soils.

Abstract A procedure for the rapid and accurate determination of water‐extractable soil nitrates is described. Use of this procedure resulted in quantitative recovery of nitrates added to soil. Reproducibility of results was high, with nitrate‐nitrogen in 40 soil samples determined on successive days differing by a maximum of 4 ppm with 33 determinations differing by 2 ppm or less. Comparison with a phenoldisulfonic acid method on 513 soil samples had a maximum difference of 7 ppm with a majority of determinations having a difference of 4 ppm or less.

Irrigated cotton lint yields as affected by phosphorus fertilizer and landscape position

Phosphorus (P) is the second most limiting nutrient in cotton (Gossypium hirsutum L.) production after nitrogen. Response to P fertilizer, however, is often hard to predict in the Southern High Plains, even with soil test-based applications. Landscape position has a strong influence on yields and perhaps on fertilizer response as well. The objective of this 5-year study (1994–1998) was to determine P fertilizer response in irrigated cotton in different landscape positions. We used an 825-m transect of end to end 15-m plots across a broad swale in an Amarillo fine sandy loam in Lamesa, TX that included three landscape positions, sideslope, bottomslope and drainageway. A randomized complete block design was used with 11 replicates and 5 P rates (0, 22.4, 33.6, 44.8, and 56 kg P ha−1). Analysis of variance showed a linear or quadratic response to P fertilizer in 3 of 5 years, and an effect of landscape position in 4 of 5 years. Four-year lint yield averages, excluding 1997, were 1355 kg ha−1 in the bottomslope position in the landscape, and 1210 and 1226 kg ha−1 on the sideslopes and in the narrow drainageway, respectively. Cross-correlation using the 55 plots as a transect revealed few effects of soil properties on lint yield, but negative correlation between yield and elevation. In 1997, the one year without a landscape effect on yield, more rain fell during the growing season than in the other 4 years. This suggests that yield potential is higher in lower landscape positions because of more favorable soil water relations. Cotton lint response to P fertilizer was evident only in the bottomslopes and in the drainageway, and was absent in the sideslopes, meaning that variable rate fertilizer applications could be linked to management zones based on landscape position.

A preliminary comparison of the ammonium acetate‐edta soil phosphorus extraction method to the bray‐1 and olsen soil phosphorus extraction methods

Abstract The ammonium acetate (NH4OAc)‐EDTA soil phosphorus (P) extraction method was compared to either the Bray‐1 soil P extraction method for non‐calcareous soils or the Olsen soil P extraction method for calcareous soils to predict com and wheat plant tissue P concentration and grain yield responses. The NH4OAc‐EDTA method predicted yield and tissue P concentration responses to P fertilizer applications more accurately than the Olsen method at three of five sites. Both the Bray‐1 and NH4OAc‐EDTA methods were successful in predicting corn and wheat yield responses to P fertilizer applications in non‐ calcareous soils in many locations. However, a direct comparison of extracted soil P levels showed that the NH4OAc‐EDTA method extracted soil P at levels which were more closely related to the Bray‐1 method than the Olsen method.