Calcium cyanamide effects on nitrogen use efficiency, yield, nitrates, and dry matter content of lettuce

A 2-yr field study was conducted to evaluate the effects of calcium cyanamide as an alternative nitrogen (N) fertilizer source on N use efficiency (NUE), yield, and quality of two types of lettuce (Lactuca sativa L.), romaine (var. longifolia, cv. Manavert) and red oak-leaf (var. crispa, cv. Aruba), grown on clay soil under a Mediterranean environment. Pretransplanting application of 120 kg ha⁻¹ of N as calcium cyanamide (120_CC) was compared with a traditional split application of 120 kg ha⁻¹ of soluble N (120_SN) consisting of 50% ammonium sulfate applied before transplanting and 50% as ammonium nitrate applied after transplanting. An unfertilized control (0-N) was included to calculate NUE indices. At harvest leaf area index, dry weight, fresh yield, dry matter concentration, and NUE indices were not affected by the N source. Leaf nitrate (NO₃^–) content was on average 55 and 41% higher in Aruba than in Manavert in the first (Exp-1) and second (Exp-2) season, respectively. Plants fertilized with 120CC had lower leaf NO₃^– content (41 and 18% in Aruba and 70 and 21% in Manavert in Exp-1 and Exp-2, respectively) compared with those fertilized with 120_SN. These results suggest calcium cyanamide may be used as an effective tool to reduce leaf NO₃^– accumulation and to produce high quality lettuce in compliance with European Regulation No. 1258/2011 while assuring competitive yields.