SEASONAL ACCUMULATION AND PARTITIONING OF NITROGEN BY LENTIL

Although wheat (Triticum aestivum L.) is the dominant crop of the semi-arid plains of Canada and the western United States, lentil (Lens culinaris Medik.) has become an important alternative crop. Sources and seasonal accumulation of N must be understood in order to identify parameters that can lead to increased N-2-fixing activity and yield. Inoculated lentil was grown in a sandy-loam soil at an irrigated site in Saskatchewan, Canada. Wheat was used as the reference crop to estimate N-2 fixation by the A-value approach. Lentil and wheat received 10 and 100 kg N ha(-1) of ammonium nitrate, respectively. Crops were harvested six times during the growing season and plant components analyzed. During the first 71 days after planting the wheat had a higher daily dry matter and N accumulation compared to lentil. However, during the latter part of the growing season, daily dry matter and N accumulation were greater for lentil. The maximum total N accumulation for lentil at maturity was 149 kg ha(-1). In contrast, wheat had a maximum N accumulation of 98 kg ha(-1) in the Feekes 11.1 stage, or 86 days after planting. The maximum daily rates of N accumulation were 3.82 kg N ha(-1) day(-1) for lentil and 2.21 kg N ha(-1) day(-1) for wheat. The percentage of N derived from N-2 fixation (% Ndfa) ranged from 0 at the first harvest to 92% at final harvest. Generative plant components had higher values for % Ndfa than the vegetative components which indicates that N in the reproductive plant parts was derived largely from current N-2 fixation and lentil continued to fix N until the end of the pod fill stage. At final harvest, lentil had derived 129 kg N ha(-1) from N-2 fixation with maximum N-2-fixing activity (4.4 kg N ha(-1) day(-1)) occurring during the early stages of pod fill. Higher maximum rates of N-2-fixing activity than net N accumulation (3.82 kg N ha(-1) day(-1)) may have been caused by N losses like volatilization. In addition, lentil provided a net N contribution to the soil of 59 kg ha(-1) following the removal of the grain.