The effect of density and foliar application of humic acid on quantitative yield and nutrient uptake of maize (Zea mays L.) under drought stress conditions

Introduction Corn scientific name (zea mays L) and annual monocot plants are poaceaae family. The corn is C4 and is native to the tropical region. The breadth of its degree of adaptation and adaptation makes it possible to cultivate it in temperate and cold regions. The corn is the third highest cereal after wheat and rice production, but its production is equal to the production volume of each of the world's two grains. The agricultural sector and its systems, with more than 90 percent of the country's water consumption, are the largest water consumer, wasting 80 percent of its traditional irrigation systems. Therefore, by reducing water resources, the reform of consumption patterns is the only way to overcome the depleted crisis. About 70% of the Earth's surface is covered by water, but unfortunately, the water crisis in many countries of the world, including the countries of the dry belt of the earth, such as Iran, is a concern. The use of natural fertilizers, including humic acid, with no harmful environmental effects can be effective in raising the yield and amount of plant biomass, especially in environmental conditions, henum humic acid is referred to as natural fertilizer of nature. Plant density, determined by number of plants per unit of land, is important in relation to the amount of crop production. Therefore, the purpose of this study was to investigate the effect of condensation and acidiferous application on quantitative yield and absorption of corn elements under drought stress conditions in Dehloran climate. Materials and methods This research was carried out in two years between 2015-2016 and 2016-2017 in a farm located in Dehloran with a longitude 47 degrees and 16 minutes east and a latitude 32 degrees and 41 minutes north and a height of 215 meters from the sea level. The experiment was carried out as split split plot in a randomized complete block design with three replications. The main factor was drought stress with three levels (optimal irrigation, irrigation cut off stage 6 to 8 leaf and irrigation cut off at crown stage). Subplots with three levels of foliar application of humic acid (control treatment (no humic acid), 2 and 4 liters per hectare humic acid) and sub-subplots including three plant densities (60, 75 and 90 thousand plants per hectare). Results The results of combined analysis of variance showed that the effect of drought stress and humic acid on grain yield, 1000 seed weight, number of seeds per ear, zinc concentration, iron concentration and protein content were significant. In drought stress conditions, grain yield and nutrient uptake, such as iron, zinc and phosphorus, decreased but the protein content increased. The highest grain yield (9580 kg.ha-1) was related to irrigation. Humic acid spraying increased seed yield, zinc concentration and grain iron content. With increasing water deficit in soil, the effect of humic acid application on seed yield significantly decreased. Grain yield and protein percentage had a positive correlation with increasing plant density. Conclusion In general, the results showed that irrigation, in addition to higher reliability and higher levels of yield, also makes it more efficient to use valuable inputs such as humic acid fertilizer. Under favorable moisture conditions, the increase of humic acid levels was associated with a significant increase in yield, and increasing the density to the average level (75 thousand plants) had a very positive effect on grain yield. In drought stress conditions at crownflower stage, decrease in adsorption and increase of moisture content of humic acid due to water deficit in soil reduced the positive effect of increasing of humic acid on increasing grain yield. Under these conditions, the use of high density did not only increase yield but also reduced all l traits. Therefore, the approach of organic and natural fertilizers such as the humic acid foliar application, in addition to increasing yield, it can play a positive role in reducing the use of chemical fertilizers and environmental pollution, so as a natural source material, it can be used to sustain and increase crop production. Regarding the lack of observation of the negative effects of humic acid on plants and increasing quantitative yield and absorb the elements, it seems better if the plant's encounter with limited irrigation conditions during the growth period is possible, humic acid could be applied on this plant in order to increase the yield of corn.