Enhancing water productivity in cabbage cultivation under deficit irrigation strategies in semi-arid climates

Introduction

Water scarcity, in both quantity and quality, is becoming a global concern-not only in traditionally arid and semi-arid regions but even in areas with high rainfall. Agriculture, being the largest consumer of water worldwide, is often viewed as inefficient in water usage, with its water demands perceived to hold less economic value compared to other sectors. Additionally, energy assessments of agricultural activities indicate that irrigation accounts for a major portion of energy consumption compared to other farm operations. This highlights the pressing need to enhance the efficiency of water use in agriculture by improving crop water productivity. Despite this, leafy vegetables are generally considered less tolerant to water deficits compared to fruit trees. Previous research by Sammis and Wu (1989) demonstrated that cabbage yields increased proportionally with higher irrigation, reaching up to 49.3 t/ha. However, Tiwari et al. (2003) found no significant differences in cabbage yields when irrigated at 100%, 80%, and 60% of crop evapotranspiration (ETc) over a three-year period. The current study aims to evaluate the effects of deficit irrigation on cabbage growth, water use efficiency (WUE), quality traits such as total soluble solids (TSS), water content, and physiological parameters like plant height and yield. The experiment followed a Randomized Block Design (RBD) with 27 treatments, involving various combinations of water stress applied during three critical growth stages: early vegetative, head formation, and head maturation. Each treatment was replicated twice. Except for treatments T1, T14, and T27, the remaining 24 treatments involved different stress combinations as illustrated in Table 1. The term Regulated Deficit Irrigation (RDI) is more appropriate here, referring to the strategic reduction of water supply during specific, less sensitive stages of the crop's growth cycle (English et al., 1990) [2] . RDI intentionally limits irrigation to control crop water usage as a management tool, requiring precise irrigation systems like micro-irrigation, along with careful monitoring of soil moisture and irrigation timing. The ideal irrigation depth is one that maximizes profitability, either per unit of water or per land area, depending on resource constraints and strategic objectives, whether focused on food production or economic returns. The concept of opportunity cost of water applies at both farm and regional levels, aiding in optimal water allocation decisions (Lorite et al., 2007; Reca et al., 2001; Shangguan et al., 2002). English et al. (1996) [3] emphasized the importance of considering both direct irrigation costs and overall production expenses, cautioning that incomplete cost assessments might underestimate the potential benefits of deficit irrigation practices.

Materials and Methods

Study Area

The field experiment to study the effect of deficit irrigation of different quantities in cabbage (Brassica oleracea L.) cv. Superball50 was conducted during rabiseason of 2024-2025 at the Experimental Farm of Department of Horticulture, College of Horticulture, Vasantrao Naik Marathwada Krishi Vidyappeth, Parbhani. Geographically Parbhani district has the expansion of 18.45 and 20.01 North latitudes and of 76.13 and 77.26. East longitudes in the Deccan plateau. District covers an area of about 6511 square km. District has an average elevation of 457.50 meters above mean sea level. Climatically the region falls under the semi-arid and sub-tropical zone. The average maximum and minimum temperature were 33.34 ℃ and 12.52 ℃ and average maximum and minimum relative humidity were 77.04% and 25.84% respectively during crop growth period. The average wind speed was 3.31 km/hr. Average sun shine hours during cop growth period was 7.71 hours. The total rainfall during crop growth period was 0mm (no rainfall). Experiment was carried out in Randomized Block Design (RBD) with twenty-seven treatments and two replications based on different combinations of the quantity of water stress days (no stress-0.00S, 25% stress-0.25S and 50% stress-0.50S) during different crop growth stages. Vegetative Stage (VS) -up to 30 days, head stage (HS) -31 to 75 days and maturity stage (MS) -76 up to harvest. The 27 treatments were

Field water use efficiency

Where, Y = crop yield, kg/ha WR = total amount of water applied in the field, mm Deficit irrigation (DI) often leads to improved water use efficiency (WUE) for several reasons. Firstly, application efficiency (Eappl) improves when water is applied below full crop evapotranspiration (ET), as the limited water stays within the root zone, reducing losses from runoff and deep percolation. Consumption efficiency (Eet), which is the ratio of evapotranspired water to the water present in the root zone, can also increase because plants are compelled to extract water more effectively from the soil. Additionally, yield efficiency (Eyld)the proportion of biomass allocated to the harvestable part-may rise, as full irrigation often promotes excessive vegetative growth in crops like cotton and grapevines, which can be reduced through DI. In semi-arid regions, where rainfall is sparse, summers are hot and dry, and evaporative demand is high, RDI (Regulated Deficit Irrigation) has been successfully employed to manage vegetative and reproductive growth in fruit trees, leading to positive agronomic and economic outcomes (Romero et al., 2004) [4] . However, the profitability of DI strategies is heavily influenced by local factors, such as water availability and its cost, making universal economic conclusions difficult (Camp, 1998). Regarding yield components, cabbage heads were harvested at full maturity on March 20, 2025. Throughout the crop cycle, growth parameters like plant height, leaf count, and canopy spread were recorded periodically. At harvest, measurements of curd diameter, curd volume, and Total Soluble Solids (TSS) were taken, along with the determination of specific gravity of the curd. In terms of production costs, when varying irrigation depths influence both yield and the duration of the crop cycle, the cost functions become nonlinear (Capra et al., 2007 and 2008). Water savings achieved through reduced irrigation depths can be redirected to irrigate additional land, thereby boosting farm income. This added benefit is known as the opportunity cost of water. For example, 50 mm of water could be applied to 1 hectare, or 25 mm to 2 hectares, potentially increasing total profitability. In water-scarce scenarios, economic returns can be maximized by reducing water depths and expanding the irrigated area, until the product of marginal profit per hectare and the total irrigated area equals the overall farm profit. For each treatment, production costs were calculated, which included expenses for labor, seeds, fertilizers, water charges, interest on capital, system depreciation, and maintenance of the irrigation infrastructure. Gross monetary returns per hectare were computed by considering the yield from each treatment and the market price of cabbage. Net income was then determined by subtracting production costs from gross returns. The benefit-cost (B:C) ratio was calculated by dividing gross returns by production costs for every treatment. Research in DI has increasingly emphasized integrating agronomic and economic assessments to optimize its application (English, 1990) [2] . While most studies acknowledge a certain level of yield reduction under DI, they highlight its potential economic gains. For instance, English and Raja (1996) [3] analyzed DI's economic viability across crops like wheat in the USA, cotton in California, and maize in Zimbabwe. Their findings suggested that irrigation deficits ranging from 15% to 59% could be economically beneficial depending on context. For data analysis, the experiment was designed using a Randomized Block Design (RBD) with 27 treatments and 2 replications. An Analysis of Variance (ANOVA) was performed using the 'F' test, considering a significance level of 5% (p=0.05).

Results and Discussion

Estimation of Crop Water Requirement of Cabbage

ETc= Kc x ETo (mm/day), It is observed from the Kc values estimated using field method varies from 0.70 to 1.11. It is observed from Table 2, that the total depth of water applied was maximum in treatment T1 (no stress treatment) and minimum in treatment T27 (maximum stress treatment). The total depth of water applied for treatment T1 which is 0% water stress throughout the crop growth period was 345mm and the total depth of water applied for treatment T14 which is 25% water stress throughout the crop growth period was 259 mm and for treatment T27 which was 50% water stress throughout the crop growth period shown the total depth of water applied were 172 mm. Plant size was temporarily reduced by 50% ETc irrigation as compared to 100% ETc irrigation Deficit irrigation at 75% ETc had no significant effect on plant size as compared to 100% Etc irrigation. Reduced plant width 60 DAP might result from leaf senescence and wilt under temporary heat stress The water use efficiency (WUE) therefore varied significantly (P≥ 0.05) among different treatment and the increase and decrease in WUE under different treatments showed positive relationship with increase in cabbage weight. This indicates that the higher the yield obtained as a result of higher volume of water applied the lower the water use efficiency and vice versa. The low FWUE obtained could be attributed to high soil evaporation in relation to crop evapotranspiration. Therefore to increase the water use efficiency and still obtain the optimum yield, the crop should be irrigated in the evening since soil evaporation is minimal in the evening. Mulching of the soil could also be incorporated as cultural practice to minimize soil moisture evaporation

Effects of cabbage influenced by different deficit irrigation

The growth parameters viz. plant height, number of leaves, plant spread, specific gravity, moisture content and total soluble solid (TSS)were measured during the study to find the effect of deficit irrigation on plant growth parameters. The plant height, plant leaves, plant spread, specific gravity, moisture content were found maximum in treatment T1 (25.5cm, 22, 64cm, 0.8(gm/cm 3 ),92.69% respectively). Total Soluble Solid (TSS) was found maximum in T27 (6.34). The growth parameters viz.

plant height, number of leaves, plant spread, specific gravity, moisture content and total soluble solid (TSS) linearly increased with advancement of crop age and reached rich maximum after 60 DAT (at harvest) during crop growth period of cabbage in all treatments. The results indicated that water stress has significant effect on growth dynamics of plant. Mean Weight of Cabbage Heads In Kilograms. mean head weight was maximum for treatment T1 (1.331 kg) and minimum in treatment T27 (0.748 kg) Different water depths modify both yield and crop cycle length, the cost function may be nonlinear. When saved water, obtained by reducing water depths, can be used to irrigate additional land, farmers can increase their income. To maintain yield stability and conserve water in water-scarce regions like Marathwada, making RDI a promising approach for climate-resilient vegetable production.

References

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