Wheat Production, Weed Population and Soil Properties Subsequent to 20 Years of Sod as Affected by Crop Rotation and Tillage

Abstract

ABSTRACT Rising production costs, unstable cereal grain prices, soil degradation due to excessive tillage and nitrate leaching are main constraints to sustainable agriculture in the Canadian prairies. Replacing conventional tillage (CT) with no-till (NT) and cereal-fallow rotations with crop rotations comprising cereals, oilseeds and legumes is thus encouraged, but information on crop rotation by tillage interaction is scarce. Properties of a silt loam (Dark Gray Luvisol), weed population and wheat production (Triticum aestivum L.) in canola (Brassica campestris L.)-wheat-wheat (C), fallow-wheat-wheat (F), field pea (Pisum sativum L.)-wheat-wheat (P) and continuous wheat (W) cropping systems were compared under CT and NT. Percentage of water stable aggregates (WSA) was reduced after a fallow season. Soil NO3-N was similar among cropped plots which was significantly lower than fallow plots in two of the three years. Ammonium-N, extractable P and penetration resistance (PR) of soil were not affected by crop rotation. The W plots tended to have more weeds than both the first (W1) and second (W2) year wheat plots in rotations. Wheat appeared to suppress weeds better than canola, field pea or fallow. Average production of 3.95 Mg ha−1 yr−1 as grain and 10.7 Mg ha−1 yr−1 as above-ground dry matter (AGDM) by the W1 were significantly greater than the corresponding production by W2 and W. Wheat grain and AGDM production in the two years of C, F, P and W systems were not significantly different in most cases. However, cumulative yields by C, P and W systems for three years of rotation were greater than the corresponding grain and AGDM yields from F rotation by 1.10 to 4.19 and 4.3 to 8.7 Mg ha−1, respectively. Tillage did not affect NO3-N, NH4-N, P and WSA in soil but reduced its PR. The NT system provided better control of annual broadleaf weeds whereas perennial weeds were better controlled by CT. The CT system produced more grains (average of 0.42 Mg ha−1 yr−1) than NT system. Crop rotation by tillage interaction effects on soil properties, weed populations and crop yields were not significant which indicated that the crop rotations were equally effective under both the tillage systems. Benefits of crop rotation over monoculture in this study were of similar nature as in earlier studies conducted on fields already under annual cropping systems. Canola and field pea were more beneficial than wheat as previous-crop for wheat production. Replacing fallow with a crop resulted in (a) increased crop production and straw returned to soil; (b) reduced potential for leaching of NO3-N; and (c) improved water stable aggregation of soil.