جواد اعتضادی جمع

Increasing soil carbon, both globally and on a farm level, has been considered as a fundamental strategy to reduce atmospheric carbon dioxide and increase soil productivity. Because agricultural ecosystems cover 11% of the earth's surface and wheat is one of the three most important grains in the world, any study on increasing soil carbon through land management and organic additive management can lead to a better understanding of our potential for soil improvement, ecosystem services, higher biomass yields, nutrient recycling, potentially increasing agricultural and ecological productivity. Crop rotation significantly affects the sequestration capacity of atmospheric carbon dioxide, and the change of cropping systems from fallowing to continuous cultivation can affect the rate of carbon sequestration in the soil through the introduction of more organic carbon. Also, managing the use of fertilizers, especially nitrogen, will not only increase crop yields, but also increase carbon sequestration as a secondary benefit to the land. Due to the alkalinity of most soils in arid and semi-arid regions, the addition of organic matter reduces soil acidity and improves plant growth conditions, increases the ability to absorb elements such as phosphorus and iron, moreover has a positive effect on increasing biomass production and carbon sequestration.

This study was conducted to take advantage of a set of desirable crop measures in diverse production systems with the aim of improving the chemical properties of soil and carbon sequestration with a focus on wheat during the two cropping years of 2018-19 and 2019-20 in a farm in Taybad plain. In this study, the factor of the cropping system in four levels (wild rocket-wheat, fallow-wheat, mung bean-wheat and corn-wheat) and the factor of nitrogen fertilizer levels (100, 50% and without nitrogen fertilizer application) were implemented in a randomized complete block design as factorial with three replications. Soil chemical properties such as acidity, organic carbon, total nitrogen, available phosphorus and iron were measured.

The highest amount of acidity was observed in corn-wheat treatment with 50% nitrogen fertilizer supply and the lowest amount of acidity was observed in wild rocket-wheat treatment with 100% nitrogen fertilizer supply. The study of treatments shows that wild rocket and mung bean showed the best results in increasing soil organic carbon and carbon sequestration. Corn less than were able to increase soil organic carbon, although with increasing nitrogen fertilizer supply in the corn-wheat cropping system, organic carbon improved compared to the control treatment. The results also showed that wild rocket-wheat treatment with 100% nitrogen fertilizer supply experienced the highest increase (56.7%) and corn-wheat treatment with 50% nitrogen fertilizer supply experienced the lowest (21.4%) increase in soil organic carbon. Soil nitrogen was also significantly affected by the increase of soil organic carbon mainly in two treatments of wild rocket-wheat (25.6%) and mung bean-wheat (17.9%) in conditions of 100% nitrogen fertilizer supply, while fallow-wheat and Wheat maize without nitrogen fertilizer showed the highest reduction in soil nitrogen content of 15.3% and 20.5%, respectively. Phosphorus and iron levels also increased in all treatments. The results of trait correlation also showed that reducing acidity in alkaline soils is the key to success in increasing plant access to phosphorus (r = -0.37 **) and iron (r = -0.33 **). It seems that the most important factor in the improving farming practices, which leads to an increase in organic carbon and consequently soil fertility, is the removal of fallow and continuous cultivation of agricultural lands.

The results showed that soil organic carbon increased in all treatments and led to increased carbon sequestration and improved soil chemical properties. The results regarding nitrogen also showed that non-use of nitrogen fertilizer in all cropping systems reduce or stop the increase of nitrogen and the need for optimal use of nitrogen fertilizer even in the case of using cover crops or legume as a nitrogen stabilizer. Reducing acidity in alkaline soils is the key to success in increasing plant access to phosphorus, although the capacity of soil organic carbon to retain phosphorus and iron in the soil should not be underestimated. Also, cropping systems affected by the type of crop rotation had different effects on soil properties. It seems that in addition to determining the quantity and quality of plant residues, plant rotation will have a different behavior on the concentration of soil elements depending on the amount of harvest of each nutrient.

There is an urgent need to increase per capita food production to compete with high population growth while maintaining environmental sustainability. Because nitrogen plays a vital role in food production for humans and livestock, nitrogen management is essential in food production. In most cropping systems, nitrogen management seems to be a major challenge due to its high mobility and natural tendency for losses from the soil-plant system to the environment. Soil organic carbon plays a key role in improving soil ecological conditions. Adding organic matter to the soil is an excellent tool for improving physical, chemical and biological conditions and is almost always desirable. Soil organic carbon stock of crop ecosystems may be increased by improving farming practices. The application of green manure, fertilizer and the return of crop straw into the soil are known as management operations to increase soil organic carbon. Fertilizers, especially nitrogen, increase crop yield, and organic carbon is returned to the soil through roots and debris, which in most cases leads to increased soil organic carbon.

This study was conducted with the aim of utilizing a set of improving farming practices in diverse cropping systems to improve nitrogen efficiency during two crop years. Farming practices including removal of summer fallow were used by importing three crops of mung bean, corn and wild rocket in rotation plus nitrogen supply levels factor. The crop rotation factor was applied in four levels of Fallow-wheat, mung bean-wheat, corn-wheat and wild rocket-wheat and the factor of nitrogen fertilizer (0, 180 and 360 kg.ha-1) in a randomized complete block design as factorial. Soil mineral nitrogen (nitrate and ammonium) were measured before sowing wheat and grain, straw and total plant nitrogen after harvest. Uptake efficiency, utilization efficiency, agronomic efficiency and nitrogen harvest index were calculated.

The results of combined analysis of variance showed that the crop rotation and nitrogen were significantly effective (ρ ≤ 0.01) on plant nitrogen, harvest index and nitrogen efficiency. Increasing nitrogen fertilizer up to 360 kg.ha-1 increased grain nitrogen, straw nitrogen, total plant nitrogen and also nitrogen harvest index. While the best uptake, utilization and agronomic efficiency of nitrogen was observed on the treatment without nitrogen fertilizer. Comparison of the means showed that the wild rocket-wheat crop rotation had the best result among all measured traits except utilization efficiency, while the utilization efficiency in the corn-wheat crop rotation showed the best performance. The results clearly show the effect of increasing organic carbon on nitrogen availability and grain nitrogen concentration as well as the role of cover crops and legume, in increasing access to nitrogen. The amount of grain nitrogen was directly affected by the amount of nitrogen fertilizer. The highest correlation coefficient was seen between agronomic and uptake efficiency (r = 0.96**). There was also a significant inverse relationship between nitrogen harvest index and the types of calculated efficiencies. The amount of uptake efficiency and agronomic efficiency in all crop rotations except corn-wheat in the second year improved compared to the first year. The highest increase in efficiency in the second year was related to the wild rocket-wheat crop rotation. In the conditions of 360 and 180 kg.ha-1 nitrogen fertilizer, the nitrogen harvest index increased in the second year compared to the first year. While in conditions without nitrogen fertilizer, nitrogen harvest index has a significant decrease. Therefore, at least in the short term, to increase the nitrogen harvest index, the minimum supply of nitrogen fertilizer should be used, even under improving crop management conditions such as green manure, removal of fallow and introduction of legumes in rotation and return of crop residues.

Continuous cropping, removal of fallow, use of cover crops and legume and preservation of residues led to increased carbon and nitrogen sequestration in soil and consequently increase biomass and nitrogen concentration in plant tissue. On the other hand, crop rotations that increased soil organic carbon and improved soil fertility quickly improved nitrogen efficiency and nitrogen harvest index.