Effect of biological and chemical fertilizers of nitrogen and phosphorus on quantitative and qualitative productivity of maize under drought stress conditions

  The reduction of nutrients in agricultural soils is led to the intensive use of fertilizers because of low nutrients use efficiency of production systems (Taheri Oshtrinani and Fathi, 2016). An optimal level of nitrogen in the soil is requried to ensure vegetative growth, greater leaf area and proper yield with the minimum environmental consequences (Zabet et al. 2014; Bahamin, 2011). In this research chemical and biological sources of nutrients are compared for yield formation in water-stressed maize. This research was carried out to investigate the effect of nitrogen and phosphorous fertilizers on yield quantity and quality of corn under drought stress. For this purpose, a split plot experiment with 4 replications was conducted in a randomized complete block design in 2015 at the Agricultural Research Station of Mehran (33° 07' North and 46° 10' East), southwest of Ilam province. The main plot factor included 3 irrigation regims of: irrigation up to 100% field capacity (no stress control), irrigation up to 75% of field apacity (moderate drought stress) and irrigation up to 50% field capacity (severe drought stress) and factorail combination of 3 levels of nitrogen and phosphorous fertilizers (including unfertilized control) was assigned to subplots. Recommended level of nitrogen was applied in the form of chemical fertilizer (in three stages before planting, stemming and flowering), or Azotobacter (seed inoculation) and the recommended rate of phosphorus was applied either in chemical form (triple superphosphate) or biological (seed-inoculated Pseudomonas fluorescens). The effect of drought stress, nitrogen fertilizer, phosphorus fertilizer and interaction of all treatments on grain yield was significant. The highest grain yield of 12372 kg/ha was obtained with full irrigation when nitrogen and phosphorous were applied in chemical form. However, the same level of corn yield was achieved with biological nitrogen+chemical phosphorpus or chemical nitrogen+biological phosphorous. At all levels of drought stress application of triple super phosphate+azotobacter resulted to a significanty higher yield compared to unfertilized control. Based on the results under the severe drought stress (50% of field capacity) grain yield of 8093.6 kg/ha was obtained with azotobacter and triple superphosphate. The effect of drought stress, nitrogen fertilizer, phosphorus fertilizer and interaction of all factors on protein yield of corn was significant. The highest protein yield of 1105 kg//ha was achieved in full irrigation when triple supplemented was combined with azotobacter. At all levels of water stress application of triple superphosphate together with azotobacter was led to a significnatly higher protein yield compared to control so that under severe drougth stress with triple superphosphate+azotobacter the protein yield was 639.4 kg/ha. However, under moderate water stress (75% of field capacity) protein yield was 774.4 kg/ha with Pseudomonas+Azotobacter wich was significanty higher that other combination of fertilizers under moderate stress. In severe stress treatment (50% of field capacity) chlorophyll a was 15.1 mg/g of leaf fresh weight, which was 13.7% higher than full irrigation treatment. The highest amount of chlorophyll b (4.92 mg/g of leaf fresh weight) was obtained when Azotobacter was applied together with super phosphate. Regardless to the source of phosphorus fertilizer the amount of chlorophyll b was highest with Azetobacter. Protein content was also maximum (9.32%) in Azotobacter+super phosphate combination. Overall, the results of this study showed that Pseudomonas and Azotobacter in low and severe water stress conditions increased the quantitative and qualitative yield of corn. Furthermore, it can be concluded that biofertilizer Pseudomonas and Azotobacter can supply most of the nutrient requirements of maize particularly when water is limited.