Effect of P fertilization management on alfalfa forage production and on soil available P

Abstract

A field experiment designed to determine the effect of P fertilization on forage production of alfalfa seeded in pure stands or mixed with Russian Wildrye was started in 1997 on a Swinton Silt Loam at Swift Current. Phosphorus as triple superphosphate was applied either prior to seeding at rates of 20, 40 or 80 (P20, P40, and P80, respectively) or as annual mid-row band applications of 10, 20 or 40 kg P2O5/ha (A10, A20, and A40, respectively). The A40 treatment was the only fertilizer regime that consistently produced the highest forage yields and forage P concentration. While the P40 and P80 treatments produced the same forage yields as A40 in the first two years of the study, their forage yields declined thereafter. All P treatments increased forage P concentration, especially A40 that consistently produced the highest P concentration. In the last year, however the preplant treatments failed to increase P concentration. Cumulative P balances for the check and preplant treatments had identical negative slopes and intercepts proportional to the rate of P applied. Balances for the annual treatments had intercepts proportional to applied P; while the A10 treatment had a zero slope; A20 andA40 had positive slopes proportional to the application of P. The level of Olsen P in the soil followed a trend similar to that described for the balance.