Forage seed yield response to N and P fertilizers and soil nutrients in northeastern Saskatchewan

Abstract

There is no information on the effect, in northeastern Saskatchewan, of N and P fertilizers on forage seed production as influenced by these nutrients in the soil. Therefore, experiments were conducted at eight sites from 1988 to 1991 to determine the effect of N and P fertilizers and soil nutrients on seed yields of alfalfa (Medicago media Pers.), smooth bromegrass (Bromus inermis Leyss.), crested wheatgrass (Agropyron cristatum L.), intermediate wheatgrass (Agropyron intermedium [Host.] Beauv.) and timothy (Phleum pratense L.). Nitrogen fertilizer (urea) was applied on grasses annually at 0, 50, 100 and 150 kg N ha−1 in factorial combination with 0, 9 and 18 kg P ha−1 (monoammonium phosphate and triple superphosphate) and on alfalfa at 0 and 50 kg N ha−1 in combination with 0, 9, 18, 26 and 53 kg P ha−1. Nitrogen significantly increased forage seed yields of all species except alfalfa. Phosphorus increased yields of forage seed for all crops except intermediate wheatgrass. The site, N, P and year and their interactions influenced seed yields. Seed yields ranged from a low of 0.29 t ha−1 for smooth bromegrass in 1990, a dry year, to a high of 1.24 t ha−1 in 1989 a cool, moist year. The yield response to N and P fertilizers was affected by available soil N and P. Relative to control, the percentage increase in grass seed yield from applied N and P fertilizers was highly related to the available soil N and P (R2 = 0.93). The estimated smooth bromegrass seed yield response to 50N–9P kg ha−1 was 0.54 t ha−1 when the soil had intermediate amounts of available N and P (2 mg N ha−1 and 8 mg P ha−1, 0- to 60-cm and 0- to 15-cm depths, respectively). On a soil that tested high in available N and P, there was no response to fertilizer. Regression equations were developed that can be used to estimate forage seed yield response of different species in relation to available soil nutrients. These results are useful for estimating the most economical return on fertilizer investment for forage seed production in Saskatchewan. Key words: Forage, seed, N, P, fertilizer, soil tests, correlation