Effect of planting method and nitrogen fertilizer on radiation use efficiency, energy balance, soil characteristics and grain yield of wheat (Triticum aestivum L.)

Food security has become one of the most important global issues due to rapid population growth and changing weather conditions, drought and heat stress. Cereals and especially wheat are among the strategic and important agricultural products and they have a special role in the food security of many countries of the world including Iran. Increasing mechanization, improving production methods and the widespread use of fertilizers during the 20th century have greatly helped to increase production and the production of agricultural products is the result of a complex interaction between various environmental factors such as soil properties and management operations. Different tillage systems have different effects on crop production in rainfed agriculture. Nitrogen is one of the most important nutrients in the production of crops, which affects the growth and performance of the plant. The purpose of this experiment was to determine the most appropriate method of seedded prepartion and the amount of nitrogen fertilizer on wheat grain yield and soil properties.

To investigate the effect of raised bed and flat planting methods and the amount of nitrogen fertilizer on soil characteristics, radiation efficiency, energy balance and grain yield of Kohdasht wheat cultivar, a factorial experiment was conducted in randomized complete block design layout with three replications in the cropping years of 2019-2020 and 2020-2021 were implemented in an experimental farm in the suburbs of Rostam Abad, Rudbar, Guilan, Iran. The experimental factors included the methods of raised bed and flat planting and nitrogen fertilizer at four levels of zero, 75, 150 and 225 kg.ha-1. Measured plant traits and other indices included plant height, 1000 grain weight, fruiting efficiency, radiation efficiency, grain protein content,  biological yield, grain yield, soil bulk density, soil porosity and energy balance.

Results showed that in the treatment of 225 kg.ha-1 of nitrogen in the method of raised bed and flat planting, the highest plant height (66.3 cm), grain yield (4908 kg.ha-1), 1000 grain weight (40 g), grain protein content (11%), fruiting efficiency (88 grain.g spike-1DW), radiation use efficiency (2.05 g.MJ-1) and biological yield (11349 kg.ha-1) were obtained. Raised bed planting methods increased the soil bulk density (1. 16 g.cm-3) and decreased soil porosity. The results showed that in terms of the total energy consumption for wheat production, the lowest and highest amounts were related to raised bed and flat methods, respectively (11681.1 and 13606.8 MJ.ha-1). The highest amount of energy consumed in the flat method was allocated to nitrogen fertilizer (51%) and fuel (19%), respectively.

Increasing nitrogen fertilizer application through the faster canopy closure and sooner maximum leaf area index caused an increase in the number of grain.spike-1, 1000 grain weight and the absorption of radiation, which ultimately increased the efficiency of radiation, biomass and grain yield. Due to the minimization of the traffic of machines on the soil by reducing the soil preparation operations, the tillage system of the raised bed planting method led to a decrease in the hours and energy required for the work of the machines per hectare compared to the flat planting method. Also, raised bed planting system along with nitrogen fertilizer increased the soil bulk density and decrease the porosity. According to the results of this experiment, it seems that the method of raised bed planting along with the consumption of 225 kg of nitrogen fertilizer.ha-1 is due to having favorable weather conditions in terms of grain yield and other studied traits for the production of Kohdasht wheat cultivar in the region, the subject of study seems to be more suitable.