Effect of organic fertilizer and nitrogen levels on plant growth characteristics in Wheat-Corn rotation

Introduction
Soil organic matter is one of the main indicators of soil quality and soil production capacity. It provides some nutrients for plant growth and improves the physical conditions of the soil. In addition to the importance of soil organic matter from an agricultural point of view, there is a deep and close relationship between the amount of soil organic matter and the amount of carbon dioxide in the air, global warming, and desertification. In addition, due to the lack of organic matter in the soils of arid and semi-arid regions, the use of organic compounds such as animal manures is considered an important and effective management factor on soil quality and improving the physical, chemical, and fertility properties of the soil. The supply sources of organic fertilizers in Iran are very diverse, which include animal manure, green manure, and all kinds of composts including urban waste composts and sewage sludge. Different sources of organic matter and their effect on plant growth have been investigated by various researchers. One of the effective ways to produce and increase crop yield is the combined use of organic and chemical fertilizers. The use of chemical fertilizers is the fastest and most reliable way to ensure soil fertility. Still, the high costs of these fertilizers, pollution, and destruction of the environment and soil are the defects of these fertilizers. Using organic fertilizers reduces the consumption of chemical fertilizers and increases the production of crops and garden crops. According to the recommendations of the Ministry of Agriculture to use fewer chemical fertilizers and to encourage farmers to use more organic fertilizers, and considering that a major part of the nitrogen in animal manure is wasted before consumption, investigating the effect of organic fertilizers on plant growth is a special priority. Therefore, this research aimed to determine the optimal levels of organic fertilizer and nitrogen for wheat cultivation in the Khorramabad region.
 
Materials and Methods
A split plot experiment in a randomized complete block design with three replications was implemented in the agricultural research station of Sarab Chengai Khorramabad during the crop year 2018-2019. This station has a moderate climate, an altitude of 1171 m asl, and an average annual rainfall of 516 mm. This station has a xeric humidity regime and a thermic temperature regime. Experimental treatments were: A- Organic fertilizer as the main treatment: M1 (control), M2 (10 tons of manure ha-1), M3 (20 tons of manure ha-1), M4 (10 tons of compost ha -1), and M5 (20 tons of compost ha -1). B- Consumption of urea fertilizer based on soil test as a sub-treatment: N1 (control), N2 (100% of fertilizer recommended based on soil test), N3 (75% of fertilizer recommended based on soil test), and N4 (50% of fertilizer recommended based on soil test). The type of crops and their rotations were wheat and corn according to common rotation in the region. Chamran variety wheat was planted on 2 November and wheat was harvested on 25 June with the amount of seed used 150 kg ha^-1, single grass 704 corn variety was planted on 1 July and corn was harvested on 26 October with the amount of seed used 30 kg ha^-1. It was done manually. All operations, such as the method and amount of irrigation water, fighting against pests and weeds, were carried out according to the advice of agricultural experts. This experiment was carried out in the form of alternating wheat and corn.
 
Results and Discussion
The results showed that in wheat, the highest straw yield in N3M2 treatment increased by 57.2% compared to control, the highest grain yield in N3M1 treatment increased by 33.6% compared to control, the highest total yield in N3M2 treatment increased by 39.8% compared to control. The highest harvest index related to the N4M4 treatment is an increase of 11.3% compared to the control, the highest number of seeds in the bunch related to the N3M2 treatment is a 50% increase compared to the control, and the highest thousand seed weight is related to the N3M4 treatment, which is a 16.6% increase compared to the control and has no significant difference with N3M3 treatment. In corn, the highest fresh weight of aerial organs related to N3M1 treatment is a 34.3% increase compared to the control, the highest nitrogen concentration of N2M2 is a 16.7% increase compared to the control, the highest seed protein is related to the N2M2 treatment is 15.8% increase compared to the control. Therefore, the use of 75% nitrogen of the soil test for wheat (187.5 kg.ha^-1 urea) and 100% of the soil test (200 kg ha^-1 urea) for corn, as well as the use of 10 t ha^-1 manure have a beneficial effect on the growth characteristics of wheat and corn. In general, for wheat, among the treatments of combined use of organic fertilizer and chemical nitrogen fertilizer, the use of 20 t.ha^-1 compost fertilizer along with 50% of recommended urea fertilizer based on the soil test (M5N4 treatment) showed the greatest effect on grain yield. In the case of corn, treatment M4N4 (use of 10 t.ha^-1 compost fertilizer along with 50% of recommended urea fertilizer based on soil test) had the greatest effect on fresh weight.
 
Conclusion
The results of this research showed that in wheat cultivation, the consumption of 75% nitrogen recommended in the soil test can increase yield and yield components compared to control. Combined use of organic fertilizer and nitrogen can significantly increase grain yield, straw, biological yield, the weight of 1000 seeds, harvest index, and the number of seeds in the cluster. The results regarding corn cultivation also showed that the use of 100% nitrogen according to the soil test has a higher efficiency than other treatments. Among the organic fertilizer treatments, 10 t ha^-1 animal manure is recommended. Therefore, to reduce the use of chemical fertilizers and increase the quality of soil properties, to prevent the reduction of soil organic matter and the destruction of the environment, the combined use of organic and chemical fertilizers is recommended.