SOIL QUALITY ATTRIBUTES AS INFLUENCED BY ANNUAL LEGUMES USED AS GREENMANURE

Tilled fallow-wheat (Triticum aestivum L.) (F-W) is the most commonly used cropping system in the semiarid Canadian prairie. However, becaus e F-W degrades soil, a partial fallow annual legume green manure (GM)- wheat system has been proposed as a viable alternative. We conducted a 6 yr study to assess the influence of four GM-W systems, compared to F-W and continuous wheat (Cont. W), on some soil quality attributes, i n a medium-textured, Aridic Haploboroll at Swift Current, Saskatchewan , Canada. The four GM legumes used were black lentil (Lens culinaris M edikus), Tangier flatpea (Lathyrus tingitanus L.), chickling vetch (La thyrus sativus L.) and feedpea (Pisum sativum L.). Analysis of soil ta ken from the 0-10 cm depth after growing wheat in the sixth year, show ed that most of the soil biochemical and physical attributes assessed were significantly improved (compared to F-W) by increasing cropping i ntensity, and by using the GM systems. A sensitivity analysis (ratio o f other treatment values to value for F-W) showed that Cent. W and the GM-W systems increased most pf the soil quality attributes tested. Am ong the GM systems the lentil-W generally increased sensitivity the mo st, while feedpea-W usually increased it the least. The labile attribu tes were more sensitive indicators of changes in soil quality than tot al organic C or N. The sensitivity of the attributes decreased in the sequence: Initial potential rate of N mineralization > C mineralizatio n > wet aggregate stability > light fraction of soil organic matter > total organic C or N. Although the amount of crop residue returned to the soil is known to have an important influence on soil quality, we w ere not able to demonstrate this in this short-term study. Crown copyr ight (C) 1998 Published by Elsevier Science Ltd. All rights reserved.