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Crop rotation and nitrogen (N) fertilization can influence soil N cycling, however, less is known about their interactive effects under varying soil and climatic conditions. We examined the interactive effects of preceding crops and N fertilizer rates on soil N cycling in canola ( Brassica napus L.) and spring wheat ( Triticum aestivum L.) cropping systems in no-till soils in the Canadian prairies. Field pea ( Pisum sativum L.), lentil ( Lens culinaris Medik), faba bean ( Vicia faba L.; faba bean-seed), canola and wheat grown for grain, and faba bean green manure (faba bean-GRM) were the preceding crops and were direct-seeded at 7 and 6 locations in 2009 and 2010, respectively. Canola and wheat were seeded in 2010 and 2011 (2012 for wheat at one site), respectively with N fertilizer applied at 0, 30, 60, 90 and 120 kg N ha −1 . Above-ground residue N returned was greatest for faba bean-GRM and lowest for canola and wheat. On average across sites, apparent in-crop N mineralization (ANM) under canola was greater following faba bean-GRM than all other preceding crops, except field pea, while under wheat, ANM was greater following all the legumes than following canola and wheat. Crop N uptake increased with N fertilizer rate, but the response was generally lower following faba bean-GRM and lentil. The N budget showed that 40–65% of crop N uptake (35–100% at highest ANM site) was possibly derived from ANM, more so following legumes, as compared to 35–60% from N fertilizer. The surplus and unaccounted N were particularly pronounced when canola and wheat were preceded by legumes rather than by canola or wheat. Our findings indicate that legumes can enhance soil N supply in no-till soils, and also highlight the importance of adjusting N fertilizer rates based on preceding crops to minimize the potential for N losses. [ABSTRACT FROM AUTHOR]

Highlights: [•] Wheat grain yield was increased after 1 year of rotation with soybean green manure. [•] Rotation with soybean decreased the fertilizer N requirement of subsequent wheat. [•] Growing soybean in the fallow period enhanced the subsequent wheat N and Zn. [•] Soil N and Zn supply capacity was improved by growing soybean as green manure. [Copyright &y& Elsevier]

Accurate estimates of manure-induced carbon retention coefficients (MCR) in soil are required when assessing carbon (C) storage and the C footprint in agricultural production systems. Eight field studies using various types and rates of manure applications on different crop rotations with durations varying from 10 to 74 years were used to quantify MCRs across diverse climatic conditions in Canada. The rate of solid cattle and swine manure had no impact on MCR which averaged 26%, whereas the MCR for liquid manure, including swine and cattle liquid manures, was much smaller, at only 5%. Under semi-arid conditions, irrigation had no impact on MCR. Compared to stockpiled manures, composted manure had a higher MCR (~36%), due to the additional stabilization of C during the composting process. The MCRs can be effectively stratified based on the type of manure affecting soil organic C differently, and the approach has potential application in regional and national estimates of soil C storage in Canada and elsewhere. • Manure application impacted soil organic carbon storage. • Manure-induced C retention coefficient (MCR) varied with type of manure. • Fresh solid cattle manure had MCR of 26% while composted manure had MCR of 36%. • The rate of fresh solid cattle manure had no impact on MCR • MCR from liquid manure, including swine and cattle, was much smaller, at only 5%. [ABSTRACT FROM AUTHOR]