Interaction Effect of Chemical and Bio-Fertilizers and Deficit Irrigation on Yield and Yield Components of Sweet Corn (Zea mays L. Var saccharata) and Some Soil Biological Activity Indices

Sweet corn (Zea mays L. Var saccharata) is an important cereal crop that referred to considerable human nutrition and industrial products of its sugar content, minerals phosphorus, magnesium, iron, zinc, vitamins in most of the literatures. The negative impacts of long-term application of chemical fertilizers on the soil, environment and human health in arid and semi-arid regions have resulted in an increase in application of biological fertilizers in these areas. The application of biological fertilizers is an environmentally-friendly approach to plant growth and production. Bio-fertilizers have been applied in agriculture to significantly reduce the application of chemical fertilizers and it is used as a strategy for improving crop productivity, sustainability soil health, environment friendly and cost effective.

This experiment was carried out as a factorial arranged as randomized complete blocks design with three replications during 2017 growing season at School of Agriculture, Shiraz University. The treatments included water regime at two levels (75% and 100% of water requirement) and five nitrogen rates and sources (no fertilizer, nitroxin, 150 kg urea, 150 kg urea + nitroxin and 300 kg urea). The traits included ear number per plant, row number per ear, grain number per row, canned grain yield, water use efficiency, ear harvest index, urease enzyme activity and soil microbial respiration. Crude protein was determined by Kjeldahl method, multiplied by the 6.25 (N × 6.25) conversion factor, and the results were then calculated as a percentage (%) and soluble sugar was measured by pocket model ATAGO refractometer. Moreover, ear harvest index was determined by the ratio of fresh grain yield (canned yield) per ear yield with husk, and urease enzyme activity and soil microbial respiration were estimated by the modified Kandeler and Gerber and Black et al's methods. Furthermore, yield and yield components were measured. Data were analyzed by using SAS 9.2 software and the means were separated using LSD test at 5% probability level.

The results showed that application of 150 kg urea + nitroxin significantly increased canned yield and its components, grain protein, grain soluble sugar, urease enzyme activity and soil microbial respiration, respectively compared to individual application of nitroxin and or 150 kg urea under water stress levels and there was no significant difference between 150 kg urea + nitroxin treatment and 300 kg urea ha-1. Normal irrigation (100% of water requirement) and combination of 300 kg urea + nitroxin, significantly increased ear number per plant (21.7 and 16.6%), row number per ear (21.4 and 21.4%), grain number per row (19.3 and 11.5%), canned grain yield (41.4 and 30.5%), water use efficiency (45 and 8.4%), ear harvest index (20.3 and 22.1%), urease enzyme activity (40.0 and 68.8%) and soil microbial respiration (12.1 and 1.6%), respectively and there was no significant difference between 150 kg urea + nitroxin and 300 kg urea compared to individual application of nitroxin and 150 kg urea. Therefore, application of nitroxin as a bio-fertilizer combined with 150 kg urea ha-1 produced the optimal canned yield and reduced nitrogen use and can be recommended in the arid and semi-arid regions.

According to the results, to improve the soil biological activity and yield and yield components of sweet corn, the combination of N150 and Ni instead of N300 is recommended and further research is also required to investigate the effects of applying Ni in combination with other bio-stimulants on yield and yield components of sweet corn.

We would like to thank the School of Agriculture, Shiraz University for their support, cooperation, and assistance throughout this research.