The Effect of Integrated management of Conservation Tillage and Lathyrus sativus Cover Cropping on Cucurbita pepo Yield and Selected Soil Quality Indicators

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.