Effect of Phosphorus Fertilization on Field Pea Nitrogen Production
A site at Froid, MT was selected for the study, with a background soil P level of 19 mg P/kg of soil. A split-plot design was used with tillage (ZT vs CT) as the main plot, and crop and P rate as the subplots. The crops were spring wheat and field pea, with both crops in rotation present each year. The P rates were 0, 20, 40 and 80 kg P205/ha, applied as MAP in year 1 and TSP in year 2. In year 1 the varying N rates in the MAP applied was balanced so that all treatments received 16 kg N/ha. Results from the project show a positive grain yield response to field pea from fertilizer P addition, with maximum yields achieved at 40 kg P205/ha. These responses were recorded even though soil test P levels would have indicated P sufficiency. The spring wheat did not respond to P application rates. Pea grain N uptake was positively influenced by fertilizer P rates, with N uptake increasing with P rate. This occurred while no difference was observed in N uptake in the pea crop residue. Soil test results show a very clear decline in soil test P levels in the absence, or with low rates of fertilizer P application. Only the 40 kg P205/ha fertilizer rate maintained soil test P at a level similar to the start of the study. We would like to evaluate seed P content as a means of determining the P balance (inputs vs removal) from the trial site.
IPNI-2006-USA-MT16
2006 Annual Interpretive Summary
Field pea fixes its own N, but is very dependent on using soil or fertilizer P, K, and S to both fix N and increase grain yields. A study was conducted at Culbertson, Montana, to evaluate the effect of fertilizer P use on field pea yields and P uptake in the grain. While the site had been cropped to fallow-wheat with no fertilizer addition, initial soil P levels in plots was greater than expected at 19 parts per million (ppm). State of Montana recommendations suggest limited P application is required to grow field peas at this level of P fertility. However, a significant yield response was still observed to increased application of P fertilizer. This suggests that fertilizer P application may be advantageous to increase field pea yields even if soil test P levels are adequate. Increasing fertilizer P rate up to 35 lb P2O5/A had no effect on seed P concentration, which was maintained at 0.364 to 0.373% over the 3 years of study. Only when 70 lb P2O5/A was applied did seed P concentration increase to a significantly higher level of 0.394%. Results suggest a grain P removal of 0.5 lb P2O5/bu for field pea and further indicate that the current estimate of 0.6 lb P2O5/bu may be high. MT-16F