Straw residues in wild rice (Zizania palustris L.) stands in northern Saskatchewan

Abstract

Straw production in wild rice stands fluctuates markedly from year to year. In the short term, heavy straw accumulation may reduce grain yields by smothering seedlings; in the long term, the balance of nutrients in a lake may be affected. An aquatic weed harvester was used to remove standing straw from part of a wild rice stand at the end of the growing season. Compared to the control plot, grain production increased twofold in the following year. However, straw production also increased significantly and may exacerbate the problem in future years. Decomposition bags containing chopped and unchopped straw were submerged in a lake to assess the rate of straw breakdown: complete decomposition may require 3 yr. Decomposition occurred most rapidly during the early part of each growing season. No difference was noted in rates of decomposition or nutrient release between the chopped and unchopped straw. Reduced light levels under straw loadings up to 5000 kg ha−1 in laboratory trials did not affect seedling development. However, seedling survival was severely reduced under artificial straw loads and none survived straw additions equivalent to 5000 kg ha−1. Key words: Wild rice, Zizania palustris, Saskatchewan, straw production, nutrient content, decomposition rates