Soil biochemical responses to intermittant tillage on Saskatchewan low disturbance cropping systems and Ethiopian vegetative terraces used in hillslope agriculture

Abstract

The pursuit of agricultural sustainability is necessary to ensure global food security into the future. To achieve sustainability, production systems around the world use different approaches. Utilizing several biological and physical indicators, this study investigates two agricultural production systems and assesses how management has affected the long-term health and sustainability of the soils. The first study assessed the effect of variable intensities of tillage on three Saskatchewan soils under low-disturbance (LD) management for the ten years prior to tillage. The soils represented were in the Grey, Black and Brown soils zones at sites located near Tisdale, Rosthern and Central Butte, Saskatchewan, respectively. A completely randomized block design utilized four treatments of varying tillage intensity. Samples were taken in spring before planting and after harvest at all sites. The soils were analyzed for microbial indicators of health by assessing dehydrogenase, urease, protease, and alkaline phosphatase activities. Microbial biomass carbon (MBC), microbial biomass nitrogen (MBN) and microbial quotient nitrogen (MQN) also were analyzed. Traditional soil nutrient and physical parameters were measured. The tillage intensities affected each parameter differently likely due to the differences in litter quality at each site. The high intensity tillage treatment decreased dehydrogenase activity at Tisdale at May, while in Rosthern dehydrogenase activity was increased in the moderate intensity tillage treatment and decreased by the high intensity tillage treatment. At Central Butte no effect was detected until October when dehydrogenase activity was increased by the low and moderate tillage intensity treatments. Protease and urease activities were affected at Rosthern only where the moderate intensity tillage treatment decreased activity relative to the control treatment. Soil physical parameters were not affected by tillage intensity; however nutrient levels were impacted by the increasing tillage intensity. Specifically, NO3- was reduced at Tisdale and was increased at Rosthern. Phosphate levels were reduced by the high tillage intensity in Rosthern whereas, with increasing tillage, the opposite occurred at Tisdale and Central Butte. The responses were strongly influenced by site characteristics, especially soil zone, organic matter content and surface litter abundance and quality. These effects were short-term, having no long-term impact on the agricultural sustainability or health of the soil, although knowledge of litter condition and quality is agronomically beneficial in order to predict soil responses to intense tillage events. iii The second part of the study was to assess the success of grass terraces on preserving the soil health of hillslope farm plots with Oxisolic soils in southern Ethiopia. Soil erosion has a devastating impact on hillslope agriculture in Ethiopia causing severe land degradation. An adjacent terraced and unterraced hillslope was chosen and sampled, along with a second unterraced slope for comparison. These soils were analyzed for dehydrogenase, alkaline phosphatase, and urease activities, as well as total C and total N. The plots above the terraces [terraced upper and unterraced upper] had higher urease activities than the plots below [terraced lower and unterrraced lower]. The impact of a vegetative strip that had formed a terrace 20 years ago was still evident in consistently higher alkaline phosphatase, urease, and dehydrogenase activities than the other plots. Simple methods of erosion prevention on erosion prone hill-slopes indicated that vegetative strips leading to terracing have a positive effect on soil health and functionality, promoting the long-term agricultural productivity and sustainability of these landscapes.