NET NITROGEN MINERALIZATION FROM A GRAY LUVISOL UNDER DIVERSE CROPPING SYSTEMS IN THE PEACE RIVER REGION OF ALBERTA

Proper management of crops on Gray Luvisols requires knowledge of net soil N mineralization during the growing season. Soil samples from a l ong-term field experiment at Beaverlodge, Alberta, were used to determ ine the kinetics of net N mineralization in soil samples from differen t crop rotations. The cropping systems established in 1968 consisted o f(i) continuous barley (Hordeum vulgare L.) (CB); (ii) barley-forage ( BF) [bromegrass (Bromus inermis Leyss.) and red clover (Trifolium prat ense L.)]; (iii) continuous bromegrass (CG); and (iv) continuous legum e (red clover) (CL). The BF rotation was generally alternated every 3 yr, and each phase of the rotation ((B) under bar F and B (F) under ba r) was present in every year. Soil samples from each cropping system w ere sampled to a depth of 15 cm in 1984. Net N mineralized during a 20 -wk laboratory incubation at 30 degrees C and optimum moisture ranged from 32 to 207 mg kg(-1) soil and followed the trend (B) under bar F < CB = CG = B (F) under bar < CL. The potentially mineralizable N (N-0) ranged from 29 to 364 mg kg(-1) soil; the mineralization rate constan t (k) ranged from 0.04 to 0.26 wk(-1); and the ratio of N-0 to total N (active fraction) ranged from 1.1 to 11.4%. The net N mineralization rate of CL soil was 10-fold greater than that of the other cropping sy stems at the end of 20 wk of incubation. This suggests that the CL cro pping system provides more N than other cropping systems during the gr owing season. Results support the observation that forages improve the N-supplying power of Gray Luvisols.