Assessing the Comparative Advantage of Naked-Seeded Pumpkin (Cucurbita pepo L.) and Sunflower (Helianthus annuus L.) Intercropping as affected by Drought Stress

Limitation of water resources is one of the crucial factors that contributes to the decline in agricultural productivity (Zhang et al., 2012). Intercropping plays a pivotal role for increasing biodiversity, land use efficiency, nutrient and water use efficiencies, and enhanced ecological services. Intercropping could be one of the alternatives to address some of the associated obstacles with modern agriculture, including low yield, pest and pathogen infection, soil degradation and environmental deterioration, thereby promoting sustainable and productive agriculture. Naked-seeded pumpkin (Cucurbita pepo L.) is an herbaceous, monoecious, annual plant of the Cucurbitaceae family (Lewis et al. 1997). The plant is economically and nutritionally important and cultivated for oil and medical purposes all over the globe. Several studies have reported the chemical composition and oil characteristics of the pumpkin seed from different origins and varieties (Kostalova et al., 2009). Summer squash is used for treating Helminth and reducing bad cholesterol. There is no official data about summer squash cultivation in Iran, but many Iranian farmers cultivate summer squash in marginal lands.Due to the importance of two species of naked-seeded pumpkin and sunflower and the lack of sufficient and documented information on intercropping of these two plants under drought stress, the present experiment was conducted to measure the potential of intercropping of these two plants and investigate their response to drought stress.

In order to evaluate the effect of different levels of irrigation and planting pattern on yield quantity and quality and water use efficiency (WUE) intercropped of pumpkin and sunflower, an experiment was conducted as the split-plot based on a randomized complete block design with three replications at experiment station of the Agricultural Faculty of Bardsir, Shahid Bahonar University of Kerman in 2019. The experimental treatments were irrigation levels (90, 60 and 30% of field capacity; FC) assigned to the main plot and planting patterns (sole cropping of pumpkin, sole cropping of sunflower, additive intercropping of 100% of pumpkin + 50% of sunflower on ridge and additive intercropping of 100% of pumpkin + 50% of sunflower in furrow) as the subplot.

The results showed that the highest fruit number, single fruit weight, fruit, seed and oil yields of pumpkin were obtained in additive intercropping of 100% of pumpkin + 50% of sunflower in furrow. With increasing drought stress level, the superiority of the furrow planting pattern relative to sole cropping was more evident for pumpkin. The largest head diameter (33 cm) and highest seed per head (1640) was found for additive intercropping of 100% of pumpkin + 50% of sunflower in furrow when irrigated with 90% of FC. In all irrigation levels, sunflower seed yield in sole cropping was significantly higher than both intercropping pattern due to its higher plant density. The maximum proline content for pumpkin (1.52 μmol g-1 FW) and sunflower (2.63 μmol g-1 FW) were observed at the two species sole cropping in severe drought stress condition. Land equivalent ratio (LER) was higher than one in all the irrigation levels and planting patterns. The highest value of WUE (0.64 kg m-3) was related to additive intercropping of 100% of pumpkin + 50% of sunflower in furrow when irrigated with 60% of FC.

The results of this study illustrated that pumpkin is a sensitive plant to drought stress, and deviation of water availability from the field capacity significantly declines the yield. The addition of sunflower in the middle of the furrow between the two rows of pumpkin could reduce the negative effects of drought stress on the plant. This planting pattern could also significantly improve the fruit and seed yields of pumpkin in both moderate and severe stress conditions. However, the addition of sunflower on the ridge and between pumpkin plants had no significant positive effect on improving pumpkin yield under drought stress, due to increased interspecific competition. Therefore, pumpkin intercropping with high height plants such as sunflower, which causes a shading effect on pumpkin and reduces evapotranspiration, can be a useful strategy under drought.