Soil quality attributes as influenced by annual legumes used as green manure

Tilled fallow-wheat (Triticum aestivum L.) (F-W) is the most commonly used cropping system in the semiarid Canadian prairie. However, because 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, in a medium-textured, Aridic Haploboroll at Swift Current, Saskatchewan, Canada. The four GM legumes used were black lentil (Lens culinaris Medikus), Tangier flatpea (Lathyrus tingitanus L.), chickling vetch (Lathyrus sativus L.) and feedpea (Pisum sativum L.). Analysis of soil taken from the 0-10 cm depth after growing wheat in the sixth year, showed that most of the soil biochemical and physical attributes assessed were significantly improved (compared to F-W) by increasing cropping intensity, and by using the GM systems. A sensitivity analysis (ratio of 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. Among the GM systems the lentil-W generally increased sensitivity the most, while feedpea-W usually increased it the least. The labile attributes were more sensitive indicators of changes in soil quality than total organic C or N. The sensitivity of the attributes decreased in the sequence: Initial potential rate of N mineralization > C mineralization > 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 were not able to demonstrate this in this short-term study. Crown copyright (C) 1998 Published by Elsevier Science Ltd. All rights reserved.