Deficit irrigation and biological fertilizer influence on yield and trigonelline production of fenugreek

• Moderate and severe deficit irrigation resulted in 27 and 42% seed yield penalty.
• Integration of biofertilizer and chemical fertilizer significantly enhanced seed and trigonelline yield.
• Although drought stress elevated trigonelline content in the seed, trigonelline yield per (kg ha−1) was adversely affected.
• Application of biofertilizers enhanced fenugreek drought tolerance.
• By application of biofertilizers, 50–75% of the chemical N and P fertilizer can be saved.

Fenugreek (Trigonella foenum-graecum L.) is an annual leguminous crop, widely cultivated as a medicinal plant, a high quality forage crop, or a nitrogen (N) fixing cover crop around the world. There is a lack of information about the effect of irrigation and fertilization on growth and yield of this crop, especially in regions with limited water availability. In this study, we evaluated the effects of moderate (I75: 25% saving in irrigation water) and severe deficit irrigation (I50: 50% saving in irrigation water) regimes on forage, seed, and trigonelin yield of fenugreek in a semi-arid environment (Karaj, Iran). We also examined if application of bio-fertilizers (seed inoculation with Azotobacter chroococcum and Peudomoance fluorescence) could substitute the need for chemical N, phosphorus (P), and potassium (K) fertilizer in whole or in part. The field experiment was conducted in 2012 and 2013 in a split plot arrangement based on a randomized complete block design with three replications. Forage yield, seed yield, and trigonelline concentration were significantly influenced by deficit irrigation. Implementation of I75 and I50 resulted in 40 and 65% lower forage yield compared with full irrigation (I100). Averaged over fertilizer treatments and two years, fenugreek seed yield in I100 was 839 kg ha−1 which declined by 27 and 42% under I75 and I50 treatments, respectively. Accumulation of trigonelline in fenugreek seeds was elevated from 2.9 g kg−1 in I100 to 3.1 g kg−1 in I50. Fenugreek forage and seed yield, both were significantly improved when integrated fertilizers (biofertilizer + chemical fertilizer) were applied. Among the biological, chemical and integrated fertilizers, fenugreek forage and seed yield best responded to bio + 50% chemical fertilizer. The advantage of the integrated fertilizer over chemical fertilizer was even more pronounced when deficit irrigation was practiced. Fertilization had no significant effect on trigonelline concentration According to the results of this study, integration of biofertilizer + 50% chemical fertilizer could be successfully used for fenugreek production in this region toward minimizing the consumption of chemical fertilizers and improving fenugreek yield, especially under deficit irrigation regimes.