Comparison of the decomposition and N and P mineralization of canola, pea and wheat residues

Abstract.

Insight into nutrient cycling is gained by understanding the dynamics and quantifying nutrient mineralization from decomposing crop residues. Since wheat (Triticum aestivum L.), canola (Brassica napus L.) and pulse crops such as pea (Pisum sativum L.) are commonly grown in rotation, our objectives were to: (1) compare, using the mesh bag technique, the dry matter (DM) loss and release of N and P of straw and root residues of those crops in the 10–11 months following harvest, and (2) determine the influence of N fertilizer on residue decomposition and nutrient release. The no-tillage study started in autumn 1997 when straw residues were placed on the soil surface and root residues were buried in the soil, and sampled periodically through the 1998 growing season. Wheat was grown in 1998 and received 0 or 60 kg N ha^–1. The study was repeated in 1998/1999. Wheat straw decomposed more slowly than canola or pea straw (losing an average of 12%, 24% and 25%, respectively, of initial DM in 10–11 months), however, the converse was noted for root residues (42%, 26% and 19% of initial DM). Average net N mineralization from wheat, canola and pea straw was essentially 0, 0.7 and 5.6 kg N ha^–1, respectively. Phosphorus released from straw ranged from 0.5 kg ha^–1 for pea to 0.75 kg ha^–1 for canola. Net N and P mineralization from root varied little between crop species: 0.9–1.6 kg N ha^–1 and 0.1–0.3 kg P ha^–1. Nitrogen fertilization increased DM loss, and N and P release from straw residues.