Effects of Sphagnum peat and copper sulfate on productivity of a Ferro-Humic Podzol

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Sphagnum peat is an abundant resource in the Quebec boreal zone and can be used to improve water retention in sandy soils of low productivity. Our objective was to select a peat application rate suitable for growing potato (Solanum tuberosum L. 'Superior') and barley (Hordeum vulgare L. 'Chapais') on a ferro-humic podzol. The experiment was conducted in Mistassini, Quebec, from 1994 to 1997. Organic matter content (OMC) of a Parent loamy sand was 2.7–2.9% initially. Peat was applied to small plots in a 2-yr potato and 2-yr barley rotation at rates of 0 (control), 29, 48 and 68 t ha−1 on a dry weight basis. A cupric fertilizer trial (0 vs. 2.2 kg Cu ha−1) was combined with the peat treatments. A yearly potato–barley rotation was also established in a nearby field receiving 25 t peat ha−1. The arable layer of peat-amended soils was stratified into a 5.3- to 14.8-cm thick upper layer (A1) down to the limit of peat incorporation, and an underlying layer (A2), averaging 15 cm in thickness, keeping the original soil properties. The highest tuber yield, but reduced tuber specific gravity, were obtained with the 48 t ha−1 treatment compared with the control and the 29 t ha−1 treatments. Peat rates excceeding 29 t ha−1 reduced yield and quality of the barley crop. The Cu concentration in barley and potato diagnostic tissues decreased as peat rate increased. Copper was needed to counteract the detrimental effects of peat amendments on maturation, yield and quality of barley. At field scale, peat increased the lower limit of soil water content for starting irrigation from 0.12 m3m−3 in the control to 0.15 m3m−3 in the peat-amended soil. Irrigation rate should be augmented at each passage, and frequency of waterings diminished, in peat-amended soils compared with the control, due to increased water storage capacity. Peat improved the productivity of the sandy soil up to 4–5% OMC, but could induce Cu shortage in barley. Key words: Soil water, potato, Solanum tuberosum L., barley, Hordeum vulgare L.