کربن آلی

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.

Background and Objective:

Soil organic carbon in rangeland ecosystems has a variety of functions such as increasing soil fertility, controlling erosion, increasing soil water permeability and, reducing the effects of greenhouse gases. Therefore, it is a key indicator in determining soil health that affects all physical, chemical, and biological properties of soil. The large area of the country's rangelands causes a serious challenge to the use of traditional methods in estimating soil organic carbon. In such situations, the use of remote sensing capabilities can be considered as a suitable option for monitoring the organic carbon of the country's rangeland soils.  The aim of this study was to determine the most important spectral factors affecting topsoil organic carbon in two summer rangelands.

Materials and Methods:

 This research was carried out in two summer rangelands of Lazour and Asaran. The first rangeland (Lazour) with an area of 8150 hectares and an average height of 2875 meters is located in the range of eastern longitudes 52.514 to 52.694 degrees and northern latitudes 35.855 to 35.934 degrees in Tehran province. The second Rangeland (Asaran) with an area of 5642 hectares and an average height of 2465 meters is located in the range of eastern longitudes 53.265 to 53.392 degrees and northern latitudes 35.804 to 35.882 degrees in Semnan province. In this research, the data of the OLI sensor of the Landsat 8 satellite were used. After pre-processing satellite imagery of the studied areas, Top of Atmosphere (TOA) reflectance layers of bands 2 to 7 along with the variables of surface albedo, Clay index, Carbonate index, Grain Size index, NDVI, brightness, greenness, and wetness index of Tasseled cap transformation were calculated. In each of the target areas, using Digital Elevation Model (DEM) maps, the slope, aspect, and hypsometric maps were prepared and by combining the last three layers with each other, a map of homogeneous sampling units was obtained. Soil sampling was performed using the stratified-random sampling pattern. In this way, in each of the homogeneous units, according to its area, several soil samples were randomly taken from a depth of zero to 20 cm and the amount of organic carbon of the samples was measured using the Walkley-Black method.

Results and Discussion:

 The results of this study showed that the spectral variables of Top of Atmosphere (TOA) reflectance layers of bands 2 to 7 along with the variables of surface albedo, Clay index, NDVI, brightness, greenness, and wetness index of Tasseled cap transformation have a significant correlation with topsoil organic carbon (p < 0.01). Also, the results of factor analysis by principal component analysis (PCA) with eigenvalues greater than one showed that the total cumulative variance explained by the 12 variables is 91.74%, which was explained by two factors. The first factor (soil color) explained 76.6% of the variance and the second factor (vegetation and soil texture) explained 15.14% of the variance.

Conclusion:

 The results of this study confirm the existence of a significant relationship between topsoil organic carbon and spectral factors extracted from Landsat 8 OLI sensor data in semi-steppe rangelands. Because of the large area of rangelands in Iran, the use of traditional methods in estimating soil organic carbon is not possible due to the need to spend a lot of time and money. And in such situations, the use of Remote sensing (RS) capabilities can be considered as a suitable option for monitoring the topsoil organic carbon in the rangelands.