Amount of Production and Nutritional Value of Cultivated Forage Sorghum (Sorghum bicolor L.) with Integrated Application of Bio and Chemical Fertilizers under Different Irrigation Regims

Forage production has recently reduced in some arid and semi-arid countries due to intensive grazing and consecutive dryness. Increasing scarcity of water irrigation, particularly in arid and semi-arid climates where agricultural systems are dependent upon supplemental irrigation, is becoming the most important problem for producing forage.The bio fertilizers can serve a potential tool for sustaining crop production without destruction of the soil and environment. Therefore, integrated application of bio fertilizer and chemical fertilizer seems to be a sustainable approach in agricultural systems. The plant growth promoting bacteria plays an important role in the crop growth and development through secretion of growth promoting metabolites and nutrient supply. These species increase nitrogen fixation and release plant growth promoting substances and hormones and improve nutrient and water uptake.Sorghum is becoming an increasingly important forage crop in many arid and semi-arid regions of the world especially in Iran because of its advantages over corn in warm and dry climates. The objective of this study was to evaluate the effects of different fertilizer patterns and irrigation intervals on the quantity and quality of the sorghum forage.

The experiment was conducted as split plot design based on randomized complete block design (RCBD) with 15 treatments and three replications at the faculty of Agriculture, University of Maragheh during 2016. The treatments included three different irrigation regimes (irrigation after 60, 100 and 140 mm evaporation from class A evaporation pan) and five different fertilization patterns (100% chemical fertilizer, bio fertilizer, bio fertilizer+ 75% chemical fertilizer, bio fertilizer+ 50% chemical fertilizer and bio fertilizer+ 25% chemical fertilizer). In the current research, quantity and quality properties including neutral detergent fiber (NDF), acid detergent fiber (ADF), crude protein (CP), crude fiber (CF), dry matter digestibility (DMD), water soluble carbohydrate (WSC), Total digestibly nutrient (TDN), dry matter intake (DMI), Relative feed value (RFV), net energy for lactation (NEL) and ash was calculated. Analysis of variance of the data and mean comparison were carried out by MSTATC statistical software based on Duncan’s multiple range tests.

The results showed that the dry forage yield of sorghum was significantly affected by different irrigation and fertilization patterns. The highest forage yield (26.8 t.ha-1) was achieved in 100% chemical fertilizer that was not significantly different with bio fertlizer+ 75% chemical fertilizer. Also, the lowest dry forage yield (20.6 t.h-1) was observed in application of bio fertilizer. The reason for the increase of dry matter yield in integrated application of chemical and bio fertilizers is attributed to improved nutrient uptake, increased photosynthesis, and more activity of catalase and peroxidase enzymes by plant growth promoting bacteria. In addition, with increasing irrigation interval, the biomass yield of forage sorghum was significantly reduced. Decreasing the biomass yield of sorghum by increasing irrigation intervals may be due to reducing the absorption of fermentation elements, decreasing growth and leaf area, decreasing photosynthesis, increasing the damage caused by drought stress, and increasing the amount of active oxygen radicals. The highest values of DMD, TDN, RFV and NEL were achieved in bio fertilizer+ 25% chemical fertilizer. Also, the values of CP, WSC, DMI, DMD, TDN, RFV and NEL increased by enhancing irrigation intervals. Increase of the mentioned indices is attributed to decreasing of neutral detergent fiber (NDF), acid detergent fiber (ADF) content under integrated application of chemical and bio fertilizers and increasing irrigation intervals. Results showed a positive and significant correlation between sorghum dry forage yield and crude protein yield, WSC, ADF and NDF. On the other hand, there was a negative and significant correlation between ADF and NDF with CP, DMI, DMD, TDN, RFV and NEL.

Generally, the results of this experiment demonstrated that different irrigation regimes and different fertilizer patterns had a significant effect on the quantitative and qualitative traits of the sorghum forage. The values of dry forage yield, crude fiber, ADF and NDF decreased by increasing irrigation intervals, while the values of leaf to stem ratio, CF, WSC, DMI, DMD, TDN, RFV and NEL increased in this irrigation round. In comparison between different fertilization patters, the highest forage yield was achieved in 100% chemical fertilizer that was no significantly different with bio fertilizer+ 75% chemical fertilizer. Also, the integrated application of bio fertlizer+ 25% chemical fertilizer significantly increased the content of DMI, DMD, TDN, RFV and NEL. Based on the results of this study, it can be stated that the integrated application of bio fertilizers with chemical fertilizer in drought stress conditions resulted in quantitative and qualitative improvement of sorghum forage.