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.


Jed Waddell, USDA-ARS
Phone: 406-433-9402
1500 N Central Ave
Sidney, MT