جستجوی مقالات مرتبط با کلیدواژه « جرم مخصوص ظاهری » در نشریات گروه « زراعت »

Minimum tillage (MT) and no-tillage (NT) are collectively described as conservation tillage. Conservation tillage reduces production costs, saves water, increases soil organic matter, prevents soil erosion, mitigates greenhouse gases from the soil, improves air quality, protects wildlife habitat and biodiversity, improves production and ensures environmental safety. Cover crops are considered as a support for sustainable cropping system. Some researchers have declared that using cover crops or maintaining sufficient residues of previous crops increase soil fertility and soil organic matter levels in the long term. According to strategic importance of organic matter and the significant role of tillage practices and crop residue management on crop production and soil quality improvement, a 4-year field experiment was conducted to determine Cucurbita pepo yield, yield components and selected soil quality indices, under different tillage and cover crop managements.
A four-year field experiment (2011-2014) was carried out at Bu-Ali Sina University Experimental Field in Dastjerd, Hamadan, as a factorial randomized complete block design with three replications. The area is located at 37 km of Hamadan, between 48◦31' E and 35◦01' N with 330 mm annual rainfall and 1690 m altitude. Treatments consist of three levels of tillage practices (including, NT: no-tillage (direct seeding), MT: minimum tillage (chisel plowing disk) and CT: conventional tillage (moldboard plowing disk)) and two levels of cover cropping (including, C1: with legume cover crop (lathyrus sativus) and C0: without cover crop) and were applied for four consecutive years. Pumpkin (Cucurbita pepo)was planted in the fourth year. Plant and soil samples were analyzed for grain yield, seed numbers per fruit, fruit diameter, 1000-grain weight, fruit yield, soil porosity, bulk density and alkaline phosphatase activity in 2014. Data obtained were analyzed using statistical software SAS ver. 9.4 and the means were compared using LSD test at 5 % probability level.
The highest levels of grain yield (142 g m-2), seed numbers per fruit (348), fruit diameter (78.2 cm), fruit yield (3.53 kg), soil porosity (%53.7), and alkaline phosphatase activity (3413 μg ρNP g-1 h-1) were observed in minimum tillage with Legume cover crop treatment (MT-C1); the lowest amounts of aforementioned traits, however, were obtained in CT-C0 treatment. Conservation tillage treatments (no-till and minimum tillage) with Lathyrus as cover crop demonstrated the lowest soil bulk density (average 1.1 g cm-3) and the highest porosity (average 53.7%) compared to other treatments. In conventional tillage without cover crop (CT-C0) the highest soil bulk density (1.42 g cm-3) and the lowest soil porosity (40.8 %) were observed; these indicators were not statistically different from that of minimum tillage without cover crop treatment (MT-C0). Furthermore, NT-C0 and MT-C0 showed no difference for the two same indicators. No-tillage with cover crop treatment (NT-C1) demonstrated the highest phosphatase activity (3413 μg ρNP g-1 h-1). Moreover, this treatment was statistically similar to MT-C1 and CT-C1 in this respect. On the contrary, this index was significantly lowest (1861 μg ρNP g-1 h-1) in the traditional management (CT-C0). Cover crops increase available nutrients, microbial population, microbial biomass activity and moderate soil temperature by enhancing soil organic matter. Conservation tillage on its part further improves these effects by preventing the rapid decomposition of organic matter, which eventually increases pumpkin yield and yield components as well as soil quality indicator.
Generally, after four years of applying different tillage practices with legume cover cropping, it was concluded that incorporation of Lathyrus sativus cover cropping with conservation tillage (either no-tillage or minimum tillage) is the most appropriate management for the studied area (Hamadan) in view of pumpkin yield and soil quality improvement.

IntroductionThe impact of agronomy on the subsequent product in rotational cropping systems depends on factors such as plant type, duration of crop growth, soil moisture content, tillage type, irrigation method, the amount of nitrogen fertilizer, quantity and quality of returned crop residues to the soil. Prior cultivated crops improve the next crop yield by causing different conditions (nitrogen availability, organic matter and volume of available water) in soil. This study was conducted due to importance of corn cultivation in Khuzestan and necessity of increasing the soil organic matter, moisture conservation and in the other hand the lack of sufficient information about the relationship between soil texture, type of preparatory crop in low-tillage condition and some soil characteristics and corn growth habits. The purpose of this experiment was to evaluate the effect of residue of preparatory crops in low plowing condition in two soil types on corn yield and some soil characteristics.
Materials and MethodsThis experiment was carried out at Shooshtar city located in Khuzestan province. An experiment was performed by combined analysis in randomized complete block design in two fields and in two consecutive years with four replications. Two kinds of soil texture including: clay loam and clay sand. Five preparatory crops including: broad bean, wheat, canola, cabbage and fallow as control assigned as sub plots. SAS Ver. 9.1 statistical software was used for analysis of variance and comparison of means. Graphs were drawn using MS Excel software. All means were compared by Duncan test at 5% probability level.
Results and DiscussionThe soil texture and the type of preparatory crop influenced the characteristics of the soil and corn grain yield. Returning the broad bean residue into two types of soil caused the highest grain yield of corn 10128.6 and 9547.9 kgha-1, respectively. The control treatment in sandy loam texture had the lowest corn seed yield (6111 kg.ha-1). Therefore, in these conditions, amount of plant residues and soil texture have played an important role in improving the soil quality and corn yield, which would be lead to economic objectives of sustainable and low input and cost production. Treatment of broad bean residues in depth of 0-15 cm resulted to the highest total nitrogen of 0.121% in clay loam soil and 0.122% in loam sand soil. The return of broad bean plant residues in both soil types improved corn grain yield which can be attributed for fixing and increasing the soil nitrogen by broad bean and decrease the ratio of carbon to nitrogen in soil. It seems that the contribution of broad bean residues released nitrogen gradually, particularly at the end of corn growing season.
The results showed that treatment of wheat residues in clay loam soil had the highest carbon to nitrogen ratio (8.10%), and in sandy loam soil, treatment without plant residues had the lowest ratio of carbon to nitrogen (1.4%). Increased carbon/nitrogen ratio was the result of high ratio of carbon content to nitrogen in wheat. Burying the remains of wheat and canola led to significant decrease in soil nitrogen during growing season and a sudden increase in soil organic carbon.
Mean comparisons showed that adding wheat residues to clay loam soil had the lowest soil bulk density in depth of 0-15 cm (1.19 gcm-3) and treatment of control (no adding plant residues) to sandy loam soil had the highest soil bulk density (1.54 gcm-3). The lowest soil bulk density was observed in depth of 0-15 cm and with increase in depth, soil bulk density increased, too. It seems that high percentage of the soil moisture can lead to low soil bulk density. Combination of clay loam soil with wheat, canola and broad bean residues caused soil moisture content of 21.3%, 20.4% and 20.5%, respectively, while returning the residue of cabbage did not have a significant influence on soil moisture in comparison with control (12.9%).
ConclusionsIn general, mixture of broad bean residues with both soil types had the positive effects on corn yield and soil characteristics compared to other crop residue.

In order to study the effects of tillage methods on wheat grain and its components an experiment was conducted using randomized complete block design (RCBD) with four treatments including 1-Chisel plow in depth of 5-20 Cm, 2- Moldboard plow in depth of 15 -20 Cm, 3- Moldboard plow in depth of 25-30 Cm and 4-control (No tillage) with three replications, in Khosroshahr Research Field Station in two cropping seasons (2004-2006). Tillage treatments were conducted in the same field for two years. First year safflower was grown and in the second year wheat. Data of cone index, grain yield and its components were collected for evaluation and analysis. Results showed that the effect of different tillage methods were not significant for the grain weight, spike length, grain numbers per spike. However, there were significant (P<0.05) differences among different tillage methods for grain yield and plant height. Moldboard plow in depth of 25- 30 Cm had the highest effect on grain yield (5034 Kg/ha) and No-tillage had the lowest (2903 Kg/ha). Mold board plow in depth of 25- 30 Cm had the least cone index, soil properties, but the highest soil permeability. Among the tillage methods, moldboard plow in depth of of 25- 30 Cm compared to the other treatments had greater effect on soil cone index and grain yield.