Impact of Irrigation and Fertigation Levels on Growth, Yield Components and Yield of Aerobic Rice (Oryza sativa L.) under Drip System

Globally, rice (Oryza sativa L.) is the most predominant staple food in Asia, consumed by more than a half of the world’s population. In Asia, rice security is closely related with food security as 90% of rice is consumed in this region. In India the rice is being cultivated in 46.27 m ha, which is the largest area among all rice-growing countrieswith the production of 129.4 mt and the average productivity of 2.80 t ha^-1. In Tamil Nadu rice is cultivated in an area of 2.21 m ha, production of 7.90 m t and the average productivity of 3.56 t ha^-1 (IndiaStat, 2021-22). On the other hand, the annual amount of water available per capita is decreasing. One hectare of rice field irrigated by flooding method consumes more than 20,000 m³ of irrigation water and thereby evapotranspiration consumes 6000 to 8000 m³ (Kruzhilin et al., 2017). Conventional method of irrigation, which not only consumes huge water, but also causes severe water and nutrient losses under anaerobic condition (Naik et al., 2015). Traditional, rice farming practises not only waste water but also affect the ecosystem and diminish the efficacy of fertiliser use. Consequently, better water management is required for the cultivation of rice. Numerous strategies are being pursued to reduce water requirement of rice, such as alternate wetting and drying, system of rice intensification (SRI) and aerobic rice. In an aerobic rice, the crop is established in areas which are neither puddled nor flooded and rice is grown in an unsaturated environment with sufficient inputs and supplemental irrigation when precipitation was insufficient (Mandal et al., 2019). The water productivity of rice under aerobic conditions was 32-88 per cent higher than under flooded conditions. Drip fertigation enables the direct delivery of nutrients at the position of a substantial amount of actively growing roots and enables accurate adjustment of water and nutrient supplies to meet the crop requirements. Since, nutrients are applied to a limited soil volume, the fertilizer use efficiency also high. Contrarily, traditional fertilisation may result with major nutrient losses due to leaching, percolation and volatilization (Rekha et al., 2015). Hence, it is the need of the hour to elucidate existing information on the use of drip irrigation to rice for future strategies. Taking these points into account an investigation was carried out to evaluate the performance of different levels of drip irrigation and fertigation on growth, yield attributes and yield of aerobic rice.

The present study on the effect of drip irrigation and fertigation levels on growth and yield of aerobic rice (Oryza sativa L.) was carried out during summer 2022 and 2023 on the Research Fields of Wetland in Tamil Nadu Agricultural University, Coimbatore, Tamil Nadu, India and situated between 11°N, 77°E and 426.7 m above MSL. The soil type of the experimental site was clay loam, which belongs to the Noyyal series. The soil test result of the site revealed that pH was alkaline in nature (8.2), organic carbon content was in high (0.65%), low in nitrogen (225 kg ha^-1), medium in phosphorus (18 kg ha^-1) and high in potassium (595 kg ha^-1). During two years of experimentation period the crop was received 78.40 and 17.5 mm of actual rain fall and effective rainfall was 47.04 and 10.5 mm, respectively in summer 2022 and 2023. The mean maximum (33.77°C and 32.84°C) and minimum temperatures (23.47°C and 21.03°C) were observed, respectively during both the years of experimentation. The field experiment was taken up in three replicates of randomized complete block design with thirteen treatments. The treatments consisted with various combinations of irrigation levels, dose and type of fertilizers used (Table 1).
 

 
Seed of Co-51 variety used and maturing in about 110-120 days was planted at a spacing of 20×10 cm in rows accommodating 500000 plants ha^-1. Two uniform irrigations were given to all the treatments immediately after sowing for proper germination and establishment. Drip irrigation was given on every five days interval based on pan evaporation (Epan).
       
The irrigation was given through PVC pipe after filtering through the screen filter by 7.5 hp bore well. The pressure maintained in the system was 1.5 kg m^-2. From the sub main in line laterals are of 16 mm were laid out at spacing of 80 cm with 4lph discharge rate emitters positioned at 40 cm. Drip irrigation was schedule based on open pan evaporation as per the treatment after subtracting the effective rainfall for that period. Surface irrigation (T₁₃) was scheduled by surface method basedat 5.0 cm depth with IW/CPE ratio of 1.20 for rice. The fertilizers used for soil application were urea, di ammonium phosphate (DAP) and muriate of potash (MOP) and for fertigation calcium nitrate, mono ammonium phosphate (MAP) and potassium nitrate (KNO₃) used. The fertilizer recommendation for the crop was 100:50:50 kg NPK ha^-1, from which entire dose of P₂O₅ and K₂O and 50% of N were applied as basal remaining 50% of N in two equal splits at 30 and 60 DAS applied for treatment soil application of fertilizer through normal fertilizers (T₁₀ to T₁₃). However, fertilizer applied for treatments (T₁ to T₉) was given through fertigation in 26 equal splits at three days interval as per the treatments up to 90 DAS. The observations were recorded in experiment on five random plants at centre of row for growth components viz., plant height, no. of tillers and total drymatter production, grain and straw yield at harvest. The experimental data recorded were subjected to analysis by using Fisher’s method of Analysis of Variance (ANOVA). The levels of significance used in F and t test was p=0.05 (Gomez, 1984).

Growth parameters
 
The effect of drip fertigation and irrigation treatments on growth characters of aerobic rice had significant relation and increased as increases the fertigation levels throughout the growth period during summer 2022 and 2023 (Table 2). The findings were reported that application of DF @ 100% PE up to 30 DAS+150% PE up to 60 DAS+200% PE up to 90 DAS with 125% RDF (25% through NF+75% through WSF) was registered significantly higher plant height (92.54 and 95.95 cm), total no. of tillers m^-2 (469.78 and 478.42) and total dry matter production (TDMP) (988.21 and 1025.42 g m^-2) during summer 2022 and 2023, respectively as compared to other treatments. It was found to be on par with treatment T₆: DF at 100% PE up to 30 DAS+150% PE up to 60 DAS+200% PE up to 90 DAS with 100% RDF (25% through NF+75% through WSF) followed by T₈: DF at 75%PE up to 30 DAS+125% PE up to 60 DAS+ 175% PE up to 90 DAS with 125% RDF (50% through NF+50% through WSF) during two years of experimentation. However, significantly lower plant height (72.45 and 73.03 cm), number of tillers m-2 (338.59 and 345.52) and TDMP (577.12 and 579.04 g m^-2) was recorded with T₁: DF @ 50% PE up to 30 DAS+100% PE up to 60 DAS+150% PE up to 90 DAS with 75% RDF (75% through NF+25% through WSF) during 2022 and 2023 respectively. In general, the plant ability to grow depends on the availability of moisture and nutrients in continuous manner. The higher plant growth might be due to higher cell elongation and cell division was caused by constant availability of moisture at the root zone and an increase in nutrient uptake by the plant. The experimental outcomes are fall in line with the findings of Govindan and Grace (2012); Karthika and Ramanathan (2019); Naik et al., (2021) and Mariyappillai et al., (2022). Higher number of tiller production was noted with DF at 100% PE up to 30 DAS+150% PE up to 60 DAS+200% PE up to 90 DAS with 125% RDF (25% through NF+75% through WSF), might be due to good crop, root growth and availability of nutrients throughout growth stages which ultimately increased tiller density (Duary and Pramanik, 2019). Dry matter production increased with increased level of water and nutrients (T₉) due to water soluble fertilizer through fertigation resulted in continues supply of nutrients besides maintaining optimum water availability which lead to higher uptake of nutrients which in turn good soil aeration throughout crop growth period might have favored faster cell division and elongation focused ultimately increased plant height, tiller numbers, more number of leaves and leaf area development leading to maintain total dry matter accumulation. Similar evidence was confined with findings of Kombali et al., (2016), Yamuna et al., (2018) and Mariyappillai et al., (2022). And these may be attributed to the production of higher number of tillers and leaves because of higher uptake of moisture and nutrients due to maintenance frequent application of irrigation and use of water-soluble fertilizers. Similar results were conformity with Rekha et al., (2015), Ramadas and Ramanathan (2017) and Naik et al., (2021). Govindan and Grace (2012) studied that the non-availability of water to rice causes a decrease in the amount of photo-synthetically active radiation intercepted, which in turn causes a decrease in leaf production, leaf area, plant height, a reduction in tillering and an increase in leaf senescence. But in surface irrigation treatments with soil application of nutrients in two splits, utilization was found lower due to intermittence of partial dry and wet period as soil moisture reduced with time between two applications (Yamuna et al., 2018).
 

 
Yield components
 
Drip fertigation ultimately had significantly positive effect on the yield and yield components of aerobic rice when there were distinct variations in the yield components (Table 2 and 3). DF at 100% PE up to 30 DAS+150% PE up to 60 DAS+200% PE up to 90 DAS with 125% RDF (25% through NF+75% through WSF) obtained higher no. of filled grains panicle^-1 (107.5 and 114.5), total no. of grains panicle^-1 (122.6 and 127.1), fertility percentage (87.7 and 90.1%) and lower no. of ill-filled grains panicle^-1 (15.1 and 12.6), during summer 2022 and 2023, respectively. But it was found to be at par with DF @ 75% PE up to 30 DAS+125% PE up to 60 DAS+ 175% PE up to 90 DAS with 125% RDF (50% through NF+50% through WSF) followed by DF  at 100% PE up to 30 DAS+150% PE up to 60 DAS+200% PE up to 90 DAS with 100% RDF (25% through NF+75% through WSF) with respect to no. of filled grains panicle^-1 and total no. of grains panicle^-1. The lower number no. of filled grains panicle^-1 (58.2 and 62.4), total no. of grains panicle^-1 (83.4 and 87.5), fertility percentage (69.8 and 71.3%) and higher no. of ill-filled grains panicle^-1 (25.2 and 25.1) respectively, during both years of experimentation. The yield attributes of rice tend to be reduced when irrigation was applied at lesser PE rates. Exposure of rice plants to even mild water stress causes tiller mortality and spikelet sterility which, in turn, reduce productive tillers m^-2and filled grains panicle^-1. Similar findings were accounted by Vijayakumar et al., (2019) and Subramanian et al., (2023).
 

 
Yield
 
In the Table 4, the grain and straw yield (4316 and 5528 kg ha^-1 in 2022) and (4446 and 5775 kg ha^-1 in 2023) was recorded with DF @ 100% PE up to 30 DAS+150% PE up to 60 DAS+200% PE up to 90 DAS with 125% RDF (25% through NF+75% through WSF) was recorded significantly higher than all the treatments but on par with T₆: DF at 100% PE up to 30 DAS+150% PE up to 60 DAS+200 % PE up to 90 DAS with 100% RDF (25% through NF+75% through WSF) and T₈: DF @ 75% PE up to 30 DAS+125% PE up to 60 DAS+175% PE up to 90 DAS with 125% RDF (50% through NF+50% through WSF) during both season in 2022 and 2023, respectively. While, lower grain (2301 and 2365 kg ha^-1) and straw yield (3412 and 3403kg ha^-1) were obtained during summer 2022 and 2023 with application of T₁:DF @ 50% PE up to 30 DAS+100% PE up to 60 DAS+150% PE up to 90 DAS with 75% RDF (75% through NF+25% through WSF). The grain yield in any crop is depends upon the photosynthetic source it can build up. A sound source in terms of plant height, number of tillers to support and the number of leaves were rationally able to increase the total drymatter and later lead to higher grain yield. Production and partitioning of drymatter are vital for determination of overall yield of the crop. These results are in conformity with the findings of Anusha, (2015), Balaji et al., (2015); Rekha et al., (2015); Parthasarathi et al., (2018); Dada et al., (2020) and Naik et al., (2021). The higher grain yield was recorded with might be owing to higher conducive situation for efficient water and nutrients uptake which boost their growth and yield attributes through supply of more photosynthates towards the reproductive sink. This results were in corroborates with the findings of Duary and Pramanik (2019). Lower yield was recorded during both the years of experimentation because the lowest fertility percentage observed with drip fertigation at 50% PE up to 30 DAS+100% PE up to 60 DAS+150% PE up to 90 DAS with 75% RDF (75% through NF+25% through WSF). This might be owing to less nutrient uptake results in reduced soil moisture levels at root zone depth, which prevents assimilates from being transferred to the grains. Similar findings were too accounted by Kombali et al., (2016). There was no significance difference in harvest index among the treatments during both the year of experimentation.
 

The present study summarised that application of DF @ 100% PE up to 30 DAS+150% PE up to 60 DAS+200% PE up to 90 DAS with 125% RDF (25% through NF+75% through WSF) through drip fertigation was ideal for getting higher growth, yield components and yield as compared to soil application of 100% RDF with normal fertilizers during summer 2022 and 2023.

The Ministry of Tribal Affairs of the Government of India is gratefully acknowledged by the author for providing a fellowship to pursue the studies and for providing farm and laboratory facilities to carry out the research trials at Tamil Nadu Agriculture University, Coimbatore, Tamil Nadu.

All authors declare that they have no conflicts of interest.