Synchronization of nitrogen availability and plant nitrogen demand : nitrogen and non-nitrogen effects of lentil to subsequent wheat crops

Abstract

A study was conducted to determine (1) the N contribution of lentil (Lens culinaris Medikus) and its effect on subsequent wheat (Triticum aestivum L.) crops in the Dark Brown and Brown soil zones of Saskatchewan, (2) if synchronization of available N contributes to the rotation benefit, and (3) N fertilizer replacement value of the N effect of lentil on the subsequent wheat crop. Two approaches were used: a landscape-scale study established at Dinsmore in 1994, and a repeated small-plot study established at several locations (Dinsmore, 1993 and 1994; Clavet, Conquest, Eston and Zealandia, 1995). In the landscape-scale study, N2 fixation by lentil ranged from 28 to 46 kg ha-1, with an average of 34 kg ha -1 N and an N balance of -36 kg ha-1. In the small-plot study, N2 fixation ranged from 10 to 112 kg ha -1 with an average of 59 kg ha-1 N and an N balance of -22 kg ha-1. In the landscape-scale study, preseeding available N on the rotation that incorporated lentil was 29 and 61% higher than in the monocropped wheat in the first and second subsequent crops, respectively. The corresponding values for the small-plot study were 59 and 14%, respectively. N availability was well synchronized with the period of maximum N demand by the wheat crop in both rotations. However, both lentil-residue N and wheat-residue N were poorly synchronized with the period of maximum N demand by the wheat. The rotation effect was exhibited in higher grain yield (23% higher in the landscape-scale study, and 21% higher in the small-plot study). Approximately 10 and 70% of the rotation benefit in the landscape-scale and small plot studies, respectively, were attributed to the N effect. Nitrogen fertilizer replacement value ranged from 47 to 89 kg ha-1 N. Therefore, lentil can fix enough N and indirectly contribute to greater available N in subsequent crops than in crops following non-legumes. However, the actual amount of N derived from lentil residue is small. The greater available N is attributed to spared N and enhanced soil N mineralization. Hence, under the conditions of this study, enhancement of available N contributed more to the rotation benefit than synchronization. The high NFRV show that inclusion of lentil in the rotation can enhance available N in the cropping system and potentially reduce fertilizer N application.