Ahmet Kurunç

Seasonal changes of spatial variation of some groundwater quality variables in a large irrigated coastal Mediterranean region of Turkey

Soil and groundwater degradations have taken considerable attention, recently. We studied spatial and temporal variations of groundwater table depth and contours, and groundwater pH, electrical conductivity (EC), and nitrate (NO3) content in a large irrigated area in Western Mediterranean region of Turkey. These variables were monitored during 2009 and 2010 in previously constructed 220 monitoring wells. We analyzed the data by geostatistical techniques and GIS. Spatial variation of groundwater table depth (GTD) and groundwater table contours (GTC) remained similar across the four sampling campaigns. The values for groundwater NO3 content, EC, and pH values ranged from 0.01 to 454.1 gL(-1), 0.06 to 46.0 dS m(-1) and 6.53-9.91, respectively. Greatest geostatistical range (16,964 m) occurred for GTC and minimum (960 m) for groundwater EC. Groundwater NO3 concentrations varied both spatially and temporally. Temporal changes in spatial pattern of NO3 indicated that land use and farming practices influenced spatial and temporal variation of groundwater NO3. Several hot spots occurred for groundwater NO3 content and EC. These localities should be monitored more frequently and land management practices should be adjusted to avoid soil and groundwater degradation. The results may have important implications for areas with similar soil, land use, and climate conditions across the Mediterranean region.

Alterations in antioxidant enzyme activities and proline content in pea leaves under long-term drought stress

The effects of long-term drought stress on chlorophyll, proline, protein and hydrogen peroxide (H2O2) contents, malondialdehyde (MDA) in terms of lipid peroxidation and on the changes in the activities of antioxidant enzymes such as superoxide dismutase (SOD, EC 1.15.1.1), ascorbate peroxidase (APX, EC 1.11.1.11), catalase (CAT, EC 1.11.1.6) and peroxidase (POX; EC 1.11.1.7) in the leaves of pea (Pisum sativum L.) were studied in field conditions. Chlorophyll and protein contents in leaves decreased significantly with increased drought stress. The proline content increased markedly under water deficit. MDA amounts were elevated as a result of water shortage, whereas H2O2 content changed slightly in pea leaves exposed to drought stress. Drought stress markedly enhanced the activities of SOD, CAT and POX but slightly changed the activity of APX. We conclude that in field conditions, long-term water shortage increased the susceptibility to drought in peas.

Salinity and drought affect yield response of bell pepper similarly

Abstract There is a growing realization that an increasing number of countries are approaching full utilization of their conventional water resources and that the quantity of good-quality water supplies available to agriculture is diminishing. Effects of irrigation regime and irrigation water salinity on bell pepper including yield, fruit number and quality, vegetative and root growth, evapotranspiration and water use efficiency were investigated in this study by conducting two different experiments. Six different salinity levels of irrigation water and four different irrigation regimes were used as treatments. Considering the results from irrigation water salinity experiment, it can be concluded that as soil salinity increases, water consumption, water use efficiency, yield and other vegetative growth parameters of bell pepper were decreased. A polynomial relationship between soil salinity and water consumption was observed. It was found that bell pepper is moderately sensitive to salinity with a 1.2 dS m−1 threshold and a 10.9% slope value. In the irrigation regime experiment, limited irrigation caused decreases in water consumption, yield and vegetative growth of bell pepper. Yield response factors were close in the cases of irrigation regime (1.50) and irrigation water salinity (1.40). Total soluble solids of bell pepper were increased due to both irrigation water salinity and water application rate but not dry matter ratio. Considerable water consumption decreases because of salinity were determined. Therefore, the effect of irrigation water salinity should be considered in irrigation management to prevent excess saline water application and to protect the environment.

Response of cowpea (Vigna unguiculata) to salinity and irrigation regimes.

Abstract The effects of salinity and irrigation regimes on yield, growth, and water consumption of cowpea (Vigna unguiculata) were determined in two different experiments. The first experiment focused on cowpea responses to irrigation water with six different levels of salinity (0.7, 2.0, 3.0, 4.0, 5.0, and 7.0 dS m−1). In the second experiment four different amounts of water (1.43, 1.0, 0.75, and 0.50 times of depleted water) were applied to cowpea plants. Seed and pod yields of cowpea decreased significantly for the soil salinity values higher than 9.0 dS m−1. As soil salinity increased, water consumption of cowpea decreased. Therefore, the effect of salinity in lowering evapotranspiration should be considered in irrigation planning and scheduling of cowpea. Either excessive or limited water applications caused decreases in seed and pod yields of cowpea. Yield response factor (Ky), from the relationships between relative evapotranspiration and relative yield decrease, were 0.98 and 0.92 for pod and seed yields, respectively. It is concluded that cowpea is tolerant to water stress in terms of seed and pod yields.

Nondestructive leaf-area estimation and validation for green pepper (Capsicum annuum L.) grown under different stress conditions

Leaf area of a plant is essential to understand the interaction between plant growth and environment. This useful variable can be determined by using direct (some expensive instruments) and indirect (prediction models) methods. Leaf area of a plant can be predicted by accurate and simple leaf area models without damaging the plant, thus, provide researchers with many advantages in horticultural experiments. Several leaf-area prediction models have been produced for some plant species in optimum conditions, but not for a plant grown under stress conditions. This study was conducted to develop leaf area estimation models by using linear measurements such as lamina length and width by multiple regression analysis for green pepper grown under different stress conditions. For this purpose, two experiments were conducted in a greenhouse. The first experiment focused to determine leaf area of green pepper grown under six different levels of irrigation water salinity (0.65, 2.0, 3.0, 4.0, 5.0, and 7.0 dS m−1) and the other under four different irrigation regime (amount of applied water was 1.43, 1.0, 0.75, and 0.50 times of required water). In addition to general models for each experiment, prediction models of green pepper for each treatment of irrigation water salinity and of irrigation regime experiments were obtained. Validations of the models for both experiments were realized by using the measurements belong to leaf samples allocated for validation purposes. As a result, the determined equations can simply and readily be used in prediction of leaf area of green pepper grown under salinity and water stress conditions. The use of such models enable researchers to measure leaf area on the same plants during the plant growth period and, at the same time, may reduce variability in experiments.

Growth, yield, and water use of okra (Abelmoschus esculentus) and eggplant (Solanum melongena) as influenced by rooting volume

Abstract Many experiments are conducted in simulated confined spaces to provide controlled environments where plants are grown in pots with limited rooting volume to characterise fundamental physiological responses of plants to stress conditions such as soil water, soil salinity, irrigation water salinity, and plant nutrition. However, rooting volume in the pots can have a limiting effect on overall plant growth to varying degrees. This study was undertaken to quantify the effects of widely differing rooting volume on growth, yield, and water use of eggplant (Solanum melongena) and okra (Abelmoschus esculentus). Eggplant and okra experiments were conducted similarly, but as separate experiments. Both plants were grown in 3.6‐litre (P1), 16‐litre (P2), 36‐litre (P3), and 52‐litre (P4) pots. For eggplant and okra, evapotranspiration (ET) and all of the growth parameters including plant height, stem diameter, root and vegetative dry weight, root length, number of branches and fruit, and fruit yield significantly increased with increasing rooting volume. Pot volume started to affect plant height and ET after 3 weeks from transplanting. For both experiments, the highest yield and the highest yield based water‐use efficiency (WUEyield) were obtained from the P4 and P3 treatments, respectively. The highest WUE based on total biomass (WUEbiomass) was obtained from the P4 and P3 treatment of eggplant and okra, respectively. Both experiments exhibited similar morphological changes such as decreases in plant height, stem diameter, branching, root and vegetative dry weight, and root length to root restriction. As a result of this study it can be concluded that a pot size of 36 litres (P3) may be enough for okra growth, but even a 52‐litre (P4) pot size may not provide unrestricted rooting volume for eggplant growth.