Effect of anhydrous ammonia and broadcast-applied phosphorous and potassium on soil chemical properties in conservation tillage systems

Abstract

<p>Subsurface soil acidity resulting from repeated anhydrous ammonia (NH(,3)) applications in long-term conservation tillage systems that do not disturb the NH(,3) injection zone was studied by: (1) observation of the size, shape, and distribution of acidic zones in the field using a pH color indicator method and (2) intensive quantitative sampling of the upper 25- to 30-cm soil layer with subsequent laboratory analysis for soil pH. Soil pH of the acidic zones was generally 0.9 to 1.8 pH units lower than that of the surrounding bulk soil. In the ridge till-plant and ridge slot-plant systems studied, a distinct highly localized persistent acidic soil zone was detected in each interrow. Based on the extent and degree of acidity observed, it is concluded that yield-limiting problems due to acidification by continuous NH(,3) applications is not likely in ridge management systems. In the flat no-till systems studied, numerous persistent acidic soil zones were observed scattered throughout each interrow. It is concluded that soil acidity problems due to long-term NH(,3) usage potentially could develop in no-till systems where NH(,3) is not injected in the same vicinity each year. Efforts toward localized placement of N by the farm operator could effectively minimize potential problems due to the acidifying effects of NH(,3) in conservation tillage systems;Phosphorus (P) and potassium (K) distribution patterns in long-term conservation tillage systems were determined by sampling of the upper 25-cm soil layer. Results show that pronounced vertical stratification of P and K occurred in the ridge till-plant, ridge slot-plant, and flat no-till systems. Available P and K values for the upper 5-cm soil layer were, on the average, 3.5 times greater than those for the 5- to 15-cm soil layer. In the ridge till-plant and ridge slot-plant systems, localized high concentrations of P and K were frequently observed in the interrow zones. No marked row-interrow differences in soil P and K were detected in the flat no-till system. Based on the nutrient distribution patterns observed in this study, it is concluded that yield-limiting problems potentially could develop in ridge till-plant, ridge slot-plant, and flat no-till systems due to positional unavailability of nutrients. (Abstract shortened with permission of author.)</p>