Study of the Variations of Soil Organic Carbon and Nutrients and Sugarcane (Saccharum officinarum L.) Yield in Crop Rotations

Khuzestan province is one of the important regions for sugarcane production with more than 100,000 hectares under sugarcane cultivation. Sugarcane monoculture is common all over the world and continuing this system gradually reduces the yield and soil fertility. Monoculture systems, by creating unfavorable biological and physicochemical conditions in the soil, reduce the amount of organic carbon and nutrients in the soil. However, in an agricultural system, suitable agronomic selection, proper management of agronomic operation specially plowing, proper use of chemical and organic fertilizers, preservation of vegetation and proper management of plant residue have a decisive role in the amount and dynamics of mineral and organic elements. Various studies showed that rotation, particularly with green fertilizers, have led to breaking the pathogenic cycle and improving the physical and chemical properties of soil, including soil organic matter.

In order to evaluate the changes in the amount of carbon and organic matter, nitrogen, phosphorus and potassium residue in soil under different crop rotation conditions, this study was performed in a randomized complete block design with three replications during 2014-2016 for three consecutive years in the field of Amirkabir sugarcane Agro-Industry. The experiment treatments consisted of ten alternatives: 1) wheat-clover-sugarcane; 2) rapeseed-clover-sugarcane; 3) barley-clover-sugarcane; 4) sorghum-clover-sugarcane; 5) clover-vetch-sugarcane; 6) clover- clover- sugarcane, 7) clover- clover (third aftermath)- sugarcane, 8) clover- soybean- sugarcane, 9) clover- corn - sugarcane, and 10) fallow- fallow- sugarcane. The results showed that there was no significant difference between the changes in phosphorus in three years of experiment at both soil depths, but the amount of potassium and organic carbon was decreased during the third year of experiment. Analysis of variance showed that the amount of P, N and organic carbon content were significantly different in both soil depths under crop rotations. Also, under crop rotation, potassium and C/N ratio were different in 0-30 cm and 30-60 cm soil depths, respectively. The highest amount of nitrogen, phosphorus and carbon to nitrogen ratio were observed in clover-clover- sugarcane, fallow-fallow-sugarcane and sorghum-clover-sugarcane.

The results showed that the changes in the phosphorus content during three years of implementation of the project based on variance analysis even at 0-30 C depth, or at a depth of 60 to 30 cm, did not have a significant difference and the amount of phosphorus was remained almost constant.NitrogenThe results showed that the process of nitrogen changes during three years of experiment was based on analysis of variance at 0-30 and 30-60 cm of soil depths has significant difference and the amount of nitrogen has changed.Organic matter, Organic carbon and C:NOrganic matters of the soil is as the most effective factor in the sustainability of pasture and forest ecosystems, soil protection layer against erosion, temperature regulator, habitat and food supply for soil organisms and the main place of mineral nutrition.Potassium Potassium plays an important role in soil fertility. The statistical analysis of soil potassium showed that the amount of potassium had significant differences in two studied soil layers during three years of project implementation.Sugarcane yieldThe results showed that the highest yields were related to the crop rotation of clover-mung bean-sugarcane and clover- clover (third aftermath)-sugarcane rotations with 124 and 121 t.ha-1, respectively. Also, the lowest yield was related to the varieties of fallow-fallow-sugarcane and clover-corn-Sugarcane, with 95 and 98 t.ha-1, respectively.

The results showed that phosphorus in the soil did not change significantly during the experiment, but the amount of potassium, organic carbon and soil organic matter during the first and the second years remained constant but it decreased during the third year. Also, the implementation of different crop rotation affected soil nutrient elements. The highest amount of nitrogen, phosphorus and carbon to nitrogen ratios were observed in clover-clover- sugarcane, fallow-fallow-sugarcane and sorghum-clover-sugarcane. The impact of crop rotation on sugarcane yield also showed that cultivating legumes of clover and mung bean before sugarcane has a great influence on sugarcane yield.