NITRATE LEACHING IN A UDIC HAPLOBOROLL AS INFLUENCED BY FERTILIZATIONAND LEGUMES

An ongoing 34-yr crop rotation experiment being conducted on a heavy c lay at Indian Head, SK, allowed a snap-shot assessment to be made of t he influence of fertilization, legume green manure and legume-grass ha y crops, and frequency of cropping to monoculture hard red spring whea t (Triticum aestivum L.) on deep leaching of soil nitrate (NO3). The r esults showed that NO3 leaching was greatest when summer fallowing was most frequently employed. Although N fertilization may increase NO3-N leached, using a soil test as a guide to choosing fertilizer applicat ion rates and cropping annually will minimize NO3 leaching. Further, w e found that, although deep-rooted forage crops such as alfalfa (Medic ago sativa L.) remove NO3 and water to a depth of 2.4 m, and because l egumes increase the N supplying power of the soil, considerable NO, le aching can still occur under these systems. This is especially true if legume plowdown is followed by a fallow period, because during the fa llow period, copious net N mineralization may occur together with incr eased soil moisture storage. These results do not imply that NO3 leach ing is pervasive on the Canadian Prairies, but they do confirm certain well-known principles: viz., that NO3 leaching can be expected whenev er conditions favor NO3 accumulation and water buildup in soil. Conseq uently, it is important to keep the land cropped for a large proportio n of the time and to use fertilizers at moderate rates based on soil t ests.