PHOSPHORUS RELATIONSHIPS IN NO-TILL SMALL GRAINS

Phosphorus (P) fertilizer recommendations for no-till small grain prod uction are poorly defined. These studies were conducted to determine s mall grain-P response relative to the Olsen-P soil test and compare P- fertilizer placements with the seed and banded below and to the side o f the seed under no-till field conditions. Phosphorus rates of 0 to 26 kg P/ha were evaluated on seven spring barley (Hordeum vulgare L.), 1 1 spring wheat, and six winter wheat (Triticum aestivum L.) locations in central and northcentral Montana between 1986 and 1990. Grain yield , grain protein, test weight, above-ground crop yield, plant P concent ration at maturity, and P uptake were measured. One winter wheat locat ion had a significant yield response to P; all other locations had non -significant yield responses. Grain protein, test weight, P concentrat ion, and P uptake were all unaffected by P rate or P placement. Both t he ANOVA and paired t-test were used to analyze the P-placement data a nd were all nonsignificant. Slopes of grain yield response (grain yiel d for each P rate minus the grain yield without P), P concentration, a nd P uptake versus P rate were analyzed with the t-test; none of the P -response slopes were greater than zero. The P responses by individual crop were regressed against P rate, Olsen-P soil test, available soil water at planting, and pH. Phosphorus rate was not a significant fact or in any of the equations. Significant and useful predictive equation s for grain yield response could not be generated; however, equations predicting P concentration and P uptake were developed. The Cate-Nelso n graphical analysis was unsuccessful in estimating an Olsen-P soil te st critical level. All attempts failed to relate gain yield or grain y ield response to the Olsen-P soil test and/or P rate. When P soil test s are higher than 12 mg/kg, no-till grain growers should consider appl ying a maintenance level of P fertilizer, about 5 to 10 kg P/ha either banded below or with the seed, to maintain soil P levels.