Nitrogen dynamics in a chickpea-wheat rotation in a hummocky field
A study was initiated in 1996 to investigate N dynamics in a chickpea (Cicer arietinum L.)-wheat (Triticum aestivumL.) versus a wheat-wheat rotation, as influenced by landscape position, in Saskatchewan, Canada. Symbiotic N2 fixation, decomposition of crop residue, and the N and non-N effects of chickpea were investigated. Percentage of N derived from the atmosphere (%Ndfa) ranged from 29 to 97% in shoulders and from 38 to 95% in footslopes. According to an analysis of semivariance, only 28% of the variance in %Ndfa, measured at 0.3 m intervals, could be accounted for by spatial correlation. Wheat grown in the second year recovered 2.2% and 3.3% of the chickpea residue N, and 2.1% and 1.7% of the wheat residue N in shoulders and footslopes, respectively. Landscape position significantly influenced N recovery from chickpea residue but not wheat residue. In shoulders, approximately 35% of the chickpea residue N was recovered in the soil microbial biomass (SMB), whereas 13% and 30% was recovered in light (LF) and heavy fraction soil organic matter (HF), respectively. In footslopes, approximately 11% of the chickpea residue N was recovered in the SMB, whereas 29% and 44% was recovered in LF and HF, respectively. In contrast, approximately 13%, 22%, and 38% of wheat residue N in shoulders was recovered in the SMB, LF and HF, respectively. Approximately 15%, 25%, 33% of wheat residue N was recovered in the SMB, LF and HF, respectively, in footslopes. The influence of chickpea and wheat residue on the added N interaction (ANI) generally was low. The ANI of chickpea residue (1.1 kg ha-1 N) was higher than wheat residue (-0.8 kg ha-1 N) in footslopes, whereas there was no detectable difference between chickpea (-1.2 kg ha-1 N) and wheat residue (1.3 kg ha-1 N) in shoulders. The grain yield of wheat grown on chickpea stubble was 8% greater than that of wheat grown on wheat stubble in shoulders and 43% greater in footslopes. The 'A' value explained 52% of the yield variation suggesting that the N effect was as important as the non-N effect.