Investigating the effect of organic, biological and chemical fertilizers on the physiological and forage qualitative characteristics of lentil (Lens culinaris Medik) in rainfed conditions and supplementary irrigation

Lentil is a plant that often grows in marginal lands and in less fertile soils. Lentil with high protein content play an important role in feeding livestock in these areas. A great part of the land in Iran is classified within the arid and semi-arid zone where water scarcity is the main limiting factor for crop production. So, increasing water productivity with respect to crop yield per unit area is the best approach for rain-fed farming systems. Drought stress that occurs during the reproductive growth period, adversely affects the yield and yield components. Supplemental irrigation can be an efficient technique to cope with the limited water availability and to stabilize the crop yields. Organic matter enhances soil quality by improving soil structure, nutrient storage, and biological activity. The use of biofertilizers reduces the use of chemical fertilizers and in addition to providing nutrients in a way that is fully compatible with the natural nutrition of plants, helps to preserve the environment, fertility of agricultural lands and more and better yield of plants. On the other hand, growth-promoting bacteria that can make a symbiosis with the roots of most crops not only affect the biological fixation of nitrogen, but also increase cell division in plants, change root morphology, increase the number of root hairs, and enhance nutrient uptake. The combination of these fertilizers makes it possible for the fertilizer to provide the plant with absorbable nutrients in the initial period of growth, and in the later periods of growth, and ideal conditions are provided for plant growth and while reducing production costs, it also increases the quantitative and qualitative yield of plants. 

This factorial experiment was done as a complete randomized block design with three replications at Urmia University in 2017. Experimental treatments included once supplemental irrigation and dry farming as the first factor and application of different fertilizer resources including: chemical fertilizer (100%), biofertilizers (phosphate Barow-2 and Azotobacter) (100%), cow manure (100%), combined treatment: chemical+biofertilizer 50%, chemical+cow manure 50%, biofertilizer,+ cow manure 50%, biofertilizer+chemical+cow manure 50% and control at three replications were the second factor. Lentil plants were harvested on the 25-27th of June years. At harvest, random samples of plot for each experimental plants. The analysis of variance data was performed using GLM procedure (SAS 9.1, SAS Institute Inc., Cary, NC, USA). The effects of irrigation regimes, the application of different fertilizer resources and interactions of these two factors were analyzed using analysis of variance (ANOVA) and means were compared using Duncan's Multiple Range Test (DMRT) (P≤ 0.05).

The results showed that additional irrigation increased the percentage of protein, forage ash, water-soluble carbohydrates, digestible dry matter, and the activity of the enzyme glutathione reductase. But the highest amount of insoluble fiber in neutral and acid detergents was obtained in rainfed conditions. Also, the highest percentage of protein, forage ash, water-soluble carbohydrates, digestible dry matter and the activity of glutathione reductase enzyme were observed in the combined treatment of 50% chemical+biofertilizer+animal manure. While the use of different fertilizer sources compared to control had a significant effect on increasing the content of photosynthetic pigments and the activity of catalase enzyme in each of the irrigation conditions. Maximum forage yield (1460.52 kg/ha) and forage protein yield (336.38 kg/ha) were obtained in 50% chemical fertilizer+biofertilizer+animal manure treatment under additional irrigation conditions. Supplemental irrigation at flowering and pod filling period of Lentil enhanced the biological yield by positively influencing the development of auxiliary branches and plant height. The combined application of different fertilizer resources may improve nutrients uptake rate of the plants, thereby enhancing growth and development and leaf chlorophyll content followed by the increased level of photosynthesis and assimilation. The final result is the improvement of plant forage yield.

Application of different fertilizer resources could improve the uptake of forage yield in Lentil under supplementary irrigation. Therefore, according to the findings of this research, the combined use of different fertilizer resources to increase yield and maintain long-term production under rainfed conditions can be desirable for sustainable agriculture.