Extended Abstract



Introduction:

Water scarcity has become one of the most critical challenges to sustainable agricultural production, particularly in semi-arid regions. Efficient irrigation management and soil amendments such as biochar have shown great potential in improving soil structure, enhancing water retention, and increasing crop productivity under limited water supply. Tomato ( Solanum lycopersicum L. ) is one of the most economically important vegetable crops, yet it is highly sensitive to water deficit. The relationship between irrigation levels and crop yield can be analyzed through production functions and water use efficiency (WUE), which provide valuable insights for optimizing water productivity. Moreover, the Relative Growth Rate (RGR) serves as an important indicator to assess plant growth dynamics under different management conditions. This study aimed to evaluate the combined effects of various irrigation levels and biochar application rates on WUE, production function, and RGR of greenhouse-grown tomato. The findings are expected to contribute to improving irrigation strategies and sustainable resource use in protected cultivation systems.

Materials and Methods:

The experiment was conducted as a factorial arrangement in a randomized complete block design with four replications in the greenhouse of Lorestan University during winter and spring for 120 days. The mechanized polycarbonate greenhouse (20 × 9 m; 6 m height) provided controlled conditions, including 18–28 °C temperature, 50–70% relative humidity, and 500–600 µmol m⁻² s⁻¹ light intensity. Experimental factors included seven irrigation regimes—50 (L50), 60 (L60), 70 (L70), 80 (L80), 90 (L90), 100 (L100), and 110 (L110)% of crop water requirement based on soil moisture depletion and three levels of rice bran biochar: 0 (B0), 3 (B3), and 6 (B6) t ha⁻¹. Biochar was produced from agricultural residues using a muffle furnace under nitrogen gas at 500°C to ensure an oxygen-free environment. In total, 21 treatment combinations were applied to 84 pots, with L100 and B0 serving as the control.

Soil physical and chemical characteristics, including bulk density, pH, electrical conductivity (EC), cation exchange capacity (CEC), and organic carbon, were measured following standard .Water use efficiency (WUE) was calculated as the ratio of total fruit yield to the amount of water consumed. The production function between yield and evapotranspiration (ET) was fitted using a second-degree polynomial regression model to determine yield response to irrigation. The crop yield response factor (Ky) was also calculated according to the Stewart model (1977). Relative Growth Rate (RGR) was determined based on changes in plant biomass over. Data were statistically analyzed using ANOVA, and mean comparisons were performed using the least significant difference (LSD) test at the 5% significance level.

Results and Discussions:

The results demonstrated significant effects of both irrigation levels and rice bran biochar application on tomato yield, WUE, and growth parameters. The highest WUE value was recorded with (L90) combined with 6 t ha⁻¹ biochar (B6), indicating improved water productivity with minimal yield reduction compared to L100. The nonlinear (quadratic) relationship between yield and water use was fitted between tomato yield (Y) and cumulative water use (X), with an R² of 0.945, indicating that 94.5% of yield variation was explained by water consumption. In this study, Ky was calculated using the Doorenbos and Kassam (1979) model and was estimated at 0.77, which is lower than the FAO value for tomato (1.05). This lower Ky suggests that, under the experimental conditions, the crop exhibited reduced yield sensitivity and a degree of tolerance to water stress. In fact, the application of biochar reduced this sensitivity by improving soil moisture retention and root environment. Although Relative Growth Rate (RGR) naturally declined after early growth, biochar treatments, particularly B6, mitigated the negative effects of water stress, enhancing RGR by 10–25% and highlighting its role in promoting vegetative growth throughout the growing period.

Conclusion:

The results of this study indicated that the application of biochar combined with appropriate irrigation significantly improved tomato growth, yield, and water-use efficiency (WUE) The highest WUE was observed at 90% crop water requirement (L90) with 6 t ha⁻¹ rice bran biochar (B6), reflecting water savings without reducing yield. Biochar enhanced soil water retention, root environment, and nutrient uptake, while the quadratic production function revealed a nonlinear relationship between yield and water use, with a Ky of 0.77 indicating low yield sensitivity to water deficit. Relative Growth Rate was also increased in biochar-treated plants, particularly under optimal irrigation, highlighting improved vegetative growth and biomass accumulation. Overall, integrating biochar with precise irrigation management can enhance water productivity, maintain yield, and support sustainable agriculture in semi-arid regions.