Nitrogen Transformations under Zero and Shallow Tillage

Abstract

A field study was conducted with the objective of determining if differences occur in soil N transformations between zero and conventional tillage systems. Tillage comparisons of 2, 4, 12, and 16 yr duration were studied at four locations on Chernozemic soils in Western Canada. Determination of mineral N levels and immobilization of 15N‐urea fertilizer indicated that only slight, periodic, transient differences occurred between tillage systems. The degree of N mineralization‐immobilization turnover, which was associated with the incorporation of crop residues and level of labile organic matter in the surface soil, was not markedly affected by tillage differences. Over the growing season, fertilizer N entering the nonmicrobial biomass organic N pool increased relative to the microbial biomass pool, suggesting that in both systems N was entering more stabilized forms of organic N over time. These results would suggest that the differences in tillage system did not cause marked changes in the soil N cycle.

Distribution of15N in the soil-plant system during a four-year field lysimeter study with barley (Hordeum distichum L.) and perennial meadow fescue (Festuca pratensis Huds.)

“…2a-b) increased and then declined as the microbial biomass turned over and the labeled N was incorporated into more stable organic N fractions (Carter and Rennie, 1984b;Paul and Juma, 1981). A similar pattern is often found after addition of N-labeled plant residues (Amato and Ladd, 1980;Laddet al, 1981) or inorganic salts (Bristow et al, 1987;Carter and Rennie, 1984a;1984b;Ladd et al, 1977;Nannipieri et al, 1983). The incorporation of labeled N added to the meadow fescue in June (Fig.…”

“…Some of the fertilizer N is incorporated in non-harvested plant parts and soil microbial biomass. This N becomes progressively less available for mineralization due to chemical and biological stabilization processes (Allen et al, 1973;Broadbent and Nakashima, 1967;Carter and Rennie, 1984b;Legg et al, 1971;Smith et al, 1982). As a consequence, the contribution of the labeled N to subsequent harvests becomes smaller (Fredrickson et al, 1982;Hauck, 1971;Jansson, 1963;Power and Legg, 1984).…”

Crop and soil nitrogen status of tilled and no-tillage systems in semiarid regions of Saskatchewan

“…Although elimination of tillage can slow decomposition of residue, increase immobilization, and increase losses of N from the soil, Carter and Rennie (1984) concluded that replacement of the conventional shallow tillage techniques used on the prairies with NT would have minimal impact on the soil N cycle. Nevertheless, since cases of decreased plant N uptake continue to be reported under reduced tillage (e.g., McConkey et al 1996), the effects of tillage on soil N status warrant further investigation.…”

Managing Crop Disease through Cultural Practices

“…Thus, conservation tillage practices can lead to pathogen inoculum concentrations several orders of magnitude greater than those found under conventional tillage (Khan, 1975;McFadden & Sutton, 1975) and, as a result, plant roots growing in the upper soil layers might be more prone to pathogen infection (Sturz et al, 1997). In contrast however, increased microbial biomass and activity in the top soil layers can give rise to greater root density and root activity (Lynch & Panting, 1980;Carter & Rennie, 1984), which may offset the damaging effects of disease on yield, and might also provide a highly competitive soil environment with resulting disease-suppressive effects (Chen et al, 1988).…”