Soil Moisture deficit irrigation for water stress management in tomoto (solanum lycopersicum L.)

Abstract

The project entitled “Soil moisture deficit irrigation for water stress management in tomato (Solanum lycopersicum L.)” was conducted at Instructional Farm, College of Agriculture, Vellayani, Thiruvananthapuram, Kerala, during 2019-2025. The objectives of the study were standardization of irrigation schedule and agronomic management strategies for tomato under soil moisture deficit irrigation, standardization of nutrient source for fertigation and to find out the effect of foliar nutrition of calcium. The study also aimed to develop a suitable statistical model to explain the relationship between deficit irrigation, crop yield and quality with weather parameters. The study comprised of two experiments. The first experiment was laid out in split plot design with sixteen treatment combinations replicated four times during rabi and summer seasons of 2022-23. The main plot treatments were four irrigation levels: I100 - Irrigation to 100 % of FC (I1), I75 - Irrigation to 75% of FC (I2), I50/75 - Irrigation to 50 % of FC up to flowering stage, and 75% of FC at reproductive and maturation stage(I3),and I50 - Irrigation to 50 % of FC (I4), The subplot treatments were four combinations of two planting materials (P) and two mulching materials (M): p1m1-seedling tomato x silver- black plastic mulch, p1m2- seedling tomato x coir geotextile mulch, p2m1-tomato graft x silver-black plastic mulch and p2m2- tomato graft x coir geotextile mulch. The variety Vellayani Vijai was used as seedling and for graft Vellayani Vijai was grafted on to brinjal var Haritha (rootstock). The irrigation was given through drip irrigation based on soil moisture status as per treatments. Fertigation was provided based on recommended dose of fertilizer at 75:40:25 kg N: P2O5: K2O ha-1, modified to 68:10:18 kg ha-1 based on soil test values (KAU, 2024). Irrigation levels, planting and mulching materials significantly influenced the growth parameters of tomato during rabi and summer. Among the irrigation levels, taller plants were observed in I1 and it was on par with I2 except at 90 DAT (days after transplanting) and at harvest. Deeper roots with higher root volume were observed in I4 and was on par with I3. Among, the planting and mulching material combination, P2M1 and P2M2 resulted in higher root length, volume and weight during both the seasons. Irrigation to 100% FC (I1) resulted in higher cell membrane stability, relative water content and stomatal conductance and was on par with I2 in both the seasons except stomatal conductance during summer. Proline and malondialdehyde content in leaves exhibited the highest value in I4. Among planting and mulching materials, higher cell membrane stability and relative water content were observed in P2M1 and P2M2. The highest stomatal conductance was observed in p2m1. Among the interactions, the stomatal conductance was higher in i1p2m1 and was on par with i2p2m1 during summer. The treatment i1p2m1 recorded the highest chlorophyll content at flowering during summer. The yield attributes were significantly influenced by irrigation levels, and planting and mulching material. Quality parameters viz., ascorbic acid content, titrable acidity, total soluble solids and lycopene content were higher in I4. The yield of tomato in I1 and I2 were 26 and 24 per cent higher over I4 during rabi. In summer, I2 recorded higher yield (1314 g plant-1) which was on par with I1 (1254 g plant-1) and was significantly superior over I3 and I4. Among the planting and mulching materials, grafted tomato with plastic mulch was found superior over others. Among the interactions, i1p2m1 and i2p2m1 recorded higher yield. Nutrient uptake was also influenced by treatments and the highest uptake was recorded in I1 and P2M1. The results on post experimental soil analysis after each season revealed that there was a significant variation in soil enzymes, and available N, P and K in response to different irrigation levels, planting and mulching materials. Available N was the highest in I1, while available P and K were highest in I2. Among the treatment combinations, i2p2m1 recorded the highest net returns (₹ 9,13,458 ha-1 and ₹ 8,62,849 ha-1) during rabi and summer, respectively while the highest B:C ratio of 3.37 and 3.62 were recorded in i2p1m1 and i1p1m1 in rabi and summer, respectively. Crop co-efficient of tomato varied from 0.60 to 1.11 during the study. Seasonal consumptive use varied with irrigation levels and the highest value was recorded in I1. The highest water use efficiency of 93 and 84 kg ha mm-1 were recorded in i2p2m1 in rabi and summer, respectively. The agro meteorological parameters such as growing degree days (GDD), for vegetative phenophase varied from 397 oC d (I3 and I4) to 441 oC d (I1 and I2) and for reproductive stage from 1287 oC d to 1368 oC d. The heliothermal units (HTU), photothermal units (PTU) were the lowest in i4p1m1 and i4p1m2 and heat use efficiency (HUE) was the highest in i2p2m1. Based on the findings, alternate-day drip irrigation at 75% of field capacity in grafted tomato cultivated under plastic mulch can be recommended as an agronomically efficient practice for achieving higher productivity, superior fruit quality, and enhanced economic profitability. A robust statistical framework, MANOVA (Multivariate Analysis of Variance) model was developed to elucidate the complex relationship between deficit irrigation and multiple crop responses including yield and quality parameters. Complimenting this, a regression model was also developed and projected the long-term yield trend with weather parameters. The data set generated from experiment I were used and the model established a positive relationship between irrigation to 75 per cent FC and 100 per cent FC for higher yield and quality. Rainfall was the single weather parameter which affect the yield of tomato when simulated for ten years. The best soil moisture level (I2- Irrigation to 75% of FC), planting material (graft) and mulching material (plastic mulch) in experiment 1 were selected for experiment II which was laid out in split plot design with twelve treatment combinations and four replications during rabi of 2023-24. The main plot treatments were four nutrient sources (S): S1-100% NPK fertigation through water soluble fertilizer (WSF), S2-100% NPK fertigation through conventional fertilizer (CF), S3- 50 % NPK (WSF) + 50 % NPK (CF) and S4-100% NPK through soil (CF)) and the three sub plot treatments were Ca fertilization (F): F0- No Ca fertilization, F1- foliar application of 0.5% CAN at 1 MAT and F2-foliar application of 0.5 % CAN at 1 and 2 MAT. The objectives were to standardize nutrient sources for fertigation and to find out the effect of foliar nutrition of

Ca for productivity enhancement in grafted tomato with polythene mulch. Nutrients based on RDF modified on soil test values (63:10:18 kg N: P2O5: K2O per ha) was applied through fertigation in 30 splits at 4 days interval. The sources of fertilizers for WSF were 19:19:19, 12:61:00, 13:00:45 and urea, and CF were urea, SSP and MOP. The results revealed that 100 % NPK fertigation through WSF (S1) resulted in taller plants, more number of primary branches and higher stem girth, and was on par with S2. The highest leaf area and dry matter production were observed in S1. The physiological parameters also varied with treatments. Fertigation treatments took less number of days (39 to 41) for 50 per cent flowering. The flower clusters per plant were higher in S1 and was on par with S2. The yield attributes viz., fruits per truss, fruit set percentage, average fruit weight, yield per plant were higher in S1 and superior quality parameters were also observed with S1. The results revealed that application of nutrients through 100 % WSF (S1) or 50% through WSF or CF (S3) recorded 28.6 per cent and 18.8 per cent increased fruit yield over soil application. The foliar application of 0.5 % CAN at 1 and 2 MAT had significant influence on growth, yield and quality of grafted tomato. The foliar application of calcium (F1 and F2) produced more flower clusters per plant. Fruits per truss (6.24), fruit diameter (11.30 cm) and average fruit weight (41 g) were the highest in S1. Flower clusters and fruit diameter were significantly higher in F2 and was on par with F1. Fruits per truss (5.82) and fruit weight (39.66 g) were the highest in F2. The quality parameters viz., ascorbic acid, pH, TSS, titrable acidity and lycopene varied with nutrient sources and Ca nutrition. The total water requirement was 491.1 mm and the highest WUE (water use efficiency) were recorded in s1f2. The highest FUE (247 kg kg-1) was observed in s1f1. The highest nutrient recovery of 18 per cent and 75 per cent for N and P nutrients were observed in s1f0 over soil application. The highest uptake of N, P, K and Ca at harvest were observed in S1 and for calcium it was on par with S2. Among calcium nutrition, F2 recorded the highest uptake. Among the interactions, the highest N uptake was in s1f0 and for K uptake, s1f2 and s1f1 were on par and for Ca, the highest uptake was in s1f2.

Available nutrient status of soil after the experiment varied with the treatments. The nutrient sources had a significant influence on soil reaction (pH). Available N and P were significantly higher in S1 and available K was higher in S3 and was on par with S1. Among Ca nutrition, available N was higher in F2 and was on par with F1, whereas available K and Ca were the highest in F2. Nutrient recovery of N varied from 8.13 per cent (S) to 17.96 per cent (s1f0) over soil application and the highest recovery of P and K were observed in s1f0 (74.59 and 64.77 per cent, respectively). The highest net returns were recorded in s1f1. From the study, it could be concluded that alternate-day drip irrigation at 75% field capacity under plastic mulch significantly enhanced the yield, quality, and profitability of grafted tomato. Multivariate analysis (MANOVA) confirmed strong associations between deficit irrigation, yield and quality of tomato, while regression modeling identified rainfall as the most influential weather variable affecting long-term yield. Additionally, fertigation with water-soluble fertilizers in 30 equal splits at four-day intervals, supplemented with foliar application of 0.5 % calcium ammonium nitrate at one and two months after transplanting, further improved plant growth and fruit quality.