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.


15 Jan 2007

2006 Annual Interpretive Summary

Effect of Phosphorus Fertilization on Field Pea Nitrogen Production, 2006

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