Lentil-Wheat Rotation Enhances Fertilizer N Use Efficiency By 46%.

Annual pulse crops, such as dry pea (Pisum sativum L.) and lentil (Lens culinaris Medik.), have been used to diversify the conventional cereal-based monoculture in the semiarid Canadian prairie. However, little is known about the long-term effect of pulse-cereal rotation systems on soil N status as compared with cereal monoculture that is fertilized each year. A field study started in 1979 at the AAFC Swift Current Research and Development Centre, in southwestern Saskatchewan, compares a lentil-wheat rotation with continuous wheat monoculture. Crop input (including fertilizer types and rates) and yield are recorded each year. Averaged across 25 years (1979-2005), wheat in the lentil-wheat rotation system produced a similar amount of grain yield as in the continuous-wheat system, averaging 1860 ± 150 kg ha^-1 yr^-1, but the former did so with 29% less N fertilizer used compared to the latter. Consequently, fertilizer N use efficiency for wheat in the lentil-wheat system averaged 46% greater than in continuous-wheat (varying from 80% greater in dry years, 97% greater in normal years, and 36% greater in wet years). Lentil-rhizobia associations were shown to be an effective solar-driven N₂-fixing system in which atmospheric N₂ was transformed into ammonia that provided a large portion of the N requirements for lentil plant growth. Also, a portion of the fixed-N by the lentil plants remained in the roots, nodules, and rhizodeposits contributing to soil N pools and benefiting the subsequent wheat crop. Lentil plants had a lower aboveground biomass than wheat plants, but the higher N concentration in lentil residues provided greater N-benefits to the subsequent wheat. We conclude that a pulse-cereal alternate rotation can serve as a key component in the development of cropping system that focuses on high N use efficiency in semiarid environments.