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.


24 Aug 2006


Field pea acreage in Montana is increasing rapidly, largely in response to the crop being included under the loan program of the 2002 Farm Bill. The crop has been shown to do well in the state, and is particularly well adapted to NE Montana. As a grain legume, field pea fix their own nitrogen (N) from the atmosphere. However, the crop must obtain phosphorus (P) from the soil or fertilizer additions to help in growth, N fixation and yield formation. There is plenty of evidence to show that P fertilization can increase the yield of crops, and field pea is no exception.