Yield, 15N-uptake, and fertilizer use efficiency of irrigated and dryland wheat and lentil as measured throughout the growing season under various levels of nitrogen
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Laird-lentil and Neepawa-wheat were grown under irrigation in 1987 at the experimental Irrigation Farm at Outlook under three levels of N: 10 (N1), 50 (N2) and 100 (N3) kg of NH4NO3, double labelled with 15N. A similar experiment was conducted at the same site under dry land conditions in close vicinity to the experiment under irrigation. Both experiments were laid out as a split-plot, with main plots arranged as RCBD. Main plot treatments were lentil and wheat, sub-plot treatments were N level. Treatments were replicated four times. Crops were harvested at 44, 52, 63, 72, 88, and 101 days after planting (DAP). Dry weight of wheat was increased through N application and irrigation. Irrigated wheat yielded around 100 % more grain than dryland wheat (2539 and 1361 kg ha-1, respectively). Irrigation significantly increased the total dry weight of irrigated lentil. However, this was not translated into higher grain yield because the irrigated lentil remained largely in the vegetative growth stage. At 44 DAP, irrigated N3-lentil had accumulated significantly less N than irrigated N3-wheat (16.7 and 41.3 kg N/ha, respectively). At final harvest, total N uptake of N3-lentil, 157.5 kg N/ha, was significantly higher than for irrigated N3-wheat, 82.6 kg N/ha. Similar trends were found for dry land N3-wheat and N3-lentil with total N accumulation at final harvest of 48.7 and 89.4 kg N/ha for wheat and lentil, respectively. Comparable results were found for the other levels of applied N. There was no starter N effect (10 kg N/ha) on lentil yield. The highest N-accumulation for irrigated wheat occurred between 44 and 52 DAP; 2.8 kg N/ha/day. For irrigated lentil the highest N-accumulation occurred between 63 and 72 DAP; 6.8 kg N/ha/day. Under dryland conditions, N accumulations during comparable periods were 1.2 and 3.5 kg N/ha/day for wheat and lentil, respectively. With total N accumulation, most of the fertilizer N-uptake by irrigated and dry land wheat occurred during the first 52 DAP. Similar results were also found for irrigated lentil. Dry land lentil, however, accumulated fertilizer-N until the end of the growing season. The difference between dry land and irrigated lentil can be explained by leaching below the lentil rooting zone of N-fertilizer under irrigated conditions. Irrigated N3-wheat had a higher fertilizer use efficiency (% FUE) than irrigated N3-lentil, 32.8 versus 19.4 %. In contrast, dry land N3-wheat showed a lower FUE than dry land N3-lentil, 22.2 versus 36.4 %. Nitrogen application reduced N2-fixation activity at early growth stages for irrigated N3-lentil and throughout the growing season for dryland N3-lentil. During the total growing season irrigated N1-lentil fixed 124 kg N/ha, dryland N1-lentil 47 kg/ha.
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