جستجوی مقالات مرتبط با کلیدواژه "soil organic carbon" در نشریات گروه "زراعت"

Fallowing, which is one of the common practices in Iran's cropping systems, brings negative consequences such as soil erosion and reduction of its fertility, leaching of nutrients and, as a result, groundwater pollution. In addition, this practice increases weed infestation in an environment free of competition. Planting cover crops is one of the alternative methods to increase the quality and health of the soil and produce a healthy crop with minimal use of chemical inputs. Through competition and production and release of allelopathic substances in the soil environment, these crops are also considered as a suitable tool in suppressing weeds. The present study was conducted in order to investigate the effect of planting several species of cover crops as pure and mixed green manures on some soil characteristics and weed control.

This experiment was conducted in the form of a randomized complete block design with three replications in the Research Farm of Agriculture and Natural Resources Campus, Razi University, Kermanshah. Experimental treatments included cover crops of barley, common vetch and Persian clover in pure and mixed form at 10 levels: control (without cover crop), pure clover, pure barley, pure vetch, 50% barley + 50% clover, 50% barley +50 vetch, 50% vetch + 50% clover, 30% barley + 70% clover, 30% vetch + 70% barley, and 40% clover + 40% vetch + 20% barley. In order to cultivate cover crops, the land was first prepared by plowing and disk harrowing. Then, the seeds of cover crops were planted in plots of 7 × 6 m dimensions, using a furrower. The amount of seed used in the pure cultivation treatments of vetch, clover and barley was 60, 20 and 150 kg ha-1, respectively, and in the mixed treatments, different amounts of the seeds of each cover crop were planted based on the above-mentioned ratios. On the 30th of May (one month before planting potato) and at the stage when none of the cover crops had entered seed production stage, they were incorporated into the soil as green manures in two stages (one week apart) and at a depth of 10 to 15 cm.

The results showed that the cultivation of cover crops caused a decrease in pH and an increase in soil organic carbon compared to the control treatment, so that the lowest pH (7.32) and the highest soil organic carbon content (1.76%) were obtained from the pure barley treatment. Also, treatments of 40% clover + 40% vetch + 20% barley and 50% vetch + 50% clover caused a 38% and 36% increase in soil nitrogen, respectively, compared to the control treatment. The use of cover crops increased the content of phosphorus and potassium macronutrients in the soil both before and after potato harvest, compared to the control. The use of cover crops reduced the density of weeds in 20 and 40 days after potato cultivation, and the pure barley treatment reduced the density of weeds by 53 and 54%, respectively, compared to the control. The highest potato tuber yield was achieved under the treatments of 40% clover + 40% vetch + 20% barley and 50% vetch + 50% clover. The mentioned treatments increased the tuber yield by 71.09 and 59.79% compared to the control, respectively. The decrease in soil pH may be due to the accumulation of organic matter from crop residues and the acidification process during the mineralization of these residues, the increase in the amount of electrolytes, as well as the increase of microbial respiration and thereby the release of CO2 (5, 18). The increase in soil nitrogen availability following the application of green manures may have stemmed from the increase in root nodulation, release of a larger amount of nitrogen compounds by root nodules in the early stages of crop growth and their subsequent decomposition in later stages. Also, the increased nitrogen is at least partly due to the increase of organic matter through the return of biomass of cover crops in the cropping system (21). Covering the soil surface by cover crops and hence shading reduces weed seed germination and their subsequent growth due to competition of cover crops. In addition, during the decomposition of cover crop residues, allelopathic compounds are released in the soil environment, which affects the germination of weed seeds and establishment of their seedlings (15). Green manures obtained from cover crops increases moisture storage and improves soil fertility, enhancing the growth and yield of the main crop (16).

The results showed that the cultivation of cover crops instead of fallow increased the amount of organic carbon and macronutrients, despite decreasing the soil pH, leading to improvement in the access of the main crop to the soil nutrients. Weed control was another advantage of planting these crops. In the present study, the planting of leguminous cover crops with non-leguminous plants had the satisfactory results.

This study was conducted during summer and winter of 2018- 2019 in the agricultural research field of Shahid Chamran University. Experimental design was split- plot based on RCBD with three replications. The main plot was the type of agricultural system in three levels including conventional (Conv), organic (Org) and sustainable (Sust) (integrated between Conv and Org) and sup- plot was the type of pre- cultivated crop in sequence with wheat including cultivation of mung bean (M- W), corn (C- W), sesame (S- W) and fallow (F- W). Yield quantity (yield and its component) and quality (grain protein), an estimate of photosynthesis matter transfer index of wheat and soil organic carbon (SOC) after one double-cropping were measured. The result showed that the highest (545.04 g/m2) and the lowest (409.28 g/m2) seed yields were obtained in Conv and Org respectively. In contract, with the changing type of system from Conv to Org, grain protein was increased significantly (from 8.3 to 9.6 %). In addition, the highest (535.47 g/m2) yield of wheat was obtained from M- W double cropping. On the other hands the highest remobilization and current photosynthesis matter were obtained in the organic agricultural system with M- W and conventional with M- W double cropping. The situation of SOC showed that the highest (33.18 mg/g) SOC was obtained in the organic agricultural system with C- W double cropping. The reason for improving SOC in the organic and sustainable agricultural system was application of organic matter (compost and vermicompost) and crop residue management. Totally, from the crop ecology point of view, sustainable agricultural method with a sequence of M- W was the most desirable system.

Effect of conservation agriculture on soil properties and sesame yield in the sesame-wheat rotation

Conservation tillage methods offer considerable advantages compared to the conventional tillage; therefore, these tillage methods are widely disseminated throughout the world. Conservation tillage affects soil properties, environment, and crop yield. Results of research studies show that conservation tillage saves water in wheat production compared to the conventional tillage (Erenstein & Laxmi, 2008). Conservation tillage also increases soil organic carbon (Madejon et al., 2009) and sesame yield (Uzun et al., 2012) as compared to the conventional tillage. This study was performed to evaluate the effects of conservation tillage practices on soil properties and sesame yield in sesame-wheat crop rotation under hot climatic condition of Fars province.

This study was conducted using a randomized complete block experimental design with five treatments and four replications in Fars province from 2010 to 2013. Treatments included; 1) reduced tillage (T1), 2) wheat and sesame direct seeding (T2), 3) sesame direct seeding for four years, wheat direct seeding for the first two years and the fourth year, and conventional planting in the third year (T3), 4) wheat direct seeding for four years, sesame direct seeding for the first two years and the fourth year, and conventional planting in the third year (T4), and 5) conventional tillage (T5). Soil bulk density was measured at two soil depths including 0 to 10 and 10 to 20 cm using core samplers. Soil moisture content was measured using TDR at the soil depth of 0 to 20 cm. Soil water cumulative infiltration and infiltration rate were determined using double ring method. Soil organic carbon was measured by analyzing mixed soil samples in laboratory, and carbon dioxide emission from the soil was determined in the field using Anderson method. Sesame yield was calculated by harvesting 10 m2 area of each experimental plot. Collected data were analyzed using SAS software and Duncan's multiple range tests was used to compare the treatments means.

Results of this research indicated that tillage methods had significant effect on soil moisture content so that the maximum soil moisture content was obtained from the no-till method and the conventional tillage gave the lowest soil moisture content. Tillage methods had no significant effect on soil bulk density; therefore, conservation tillage methods did not considerably increase soil compaction. Results also showed that soil cumulative infiltration and infiltration rate were affected by tillage methods in such a way that conservation tillage practices decreased soil infiltration rate compared to the conventional tillage. Conservation tillage methods also increased soil organic carbon and decreased carbon dioxide emission from the soil as compared to the conventional tillage. Meanwhile, conservation tillage methods did not significantly decrease sesame yield relative to the conventional tillage.

Results showed that conservation tillage methods increased soil moisture retention (at most 50%) and soil organic carbon (138%) relative to the conventional tillage. Soil bulk density was not affected by tillage methods, while conservation tillage methods reduced soil water cumulative infiltration and infiltration rate compared to the conventional tillage (33%). Conservation tillage methods reduced carbon dioxide emission from the soil by 19%. Meanwhile, conservation tillage methods did not reduce sesame yield compared to conventional methods.
Acknowledgments: The authors would like to acknowledge the financial support extended by the Agriculture Organization of Fars province and Agricultural Engineering Research Institute