Effect of Drip Irrigation on Growth , Physiology , Yield and Water Use of Rice

The field experiment was conducted to investigate the effect of drip irrigation treatments such as three lateral distances (0.6 m, 0.8 m or 1.0 m lateral distance) on growth parameters physiological characters, yield and water use of rice under two discharge rates drippers (0.6 or 1.0 litre per hour emitters). Among the lateral distances, 0.8 m lateral distance adjudged as optimum spacing for its better performance in growth, physiological and yield attributes than rest of the lateral distances. Between two-discharge rates, 1.0 lph drippers out performed 0.6 lph drippers in grain yield. Interactively, laterals spaced at 0.8 m with 1.0 lph drippers exhibited better performance by way of growth parameters (such as plant height, tiller density, root biomass, total dry matter accumulation), physiological attributes (such as w, Chlorophyll content, Catalase activity and Malondialdehyde content), yield and its components (such as productive tillers, spikelet numbers, filled grain percentage, Harvest Index) along with water productivity. Drip irrigation confirms to increase in water productivity in the present study with water saving of 27.4% over the conventional aerobic rice cultivation. Enhanced physiological activities showed increased growth and yield in rice under 0.8 m lateral distance drip irrigation which is a viable tool for balanced source sink relation. Our results indicated that the lateral spacing of 0.8 m with 1.0 lph drippers is best for rice cultivation in enhancing the growth, physiology, grain yield and water productivity.


Introduction
Increasing scarcity and rising cost of water threatens the sustainability of irrigated lowland rice.It is expected that by 2025 AD, more than 17 million ha of Asia's irrigated rice would experience "physical water scarcity" and about 22 million ha might experience "economic water scarcity" (Tuong & Bouman, 2003).For producing rice, a tremendous amount of water is used for the rice irrigation under the traditional irrigation method called as a continuous deep flooding irrigation technique and, therefore, a newer method to combat water scarcity situation is warranted.Aerobic rice is an agricultural production system utilizing less water than conventional flooded rice.Rice plants under aerobic systems undergo several cycles of wetting and drying conditions (Matsuo & Mochizuki, 2009).Such a mild plant water stress at vegetative growth stage decreased tiller number (Cruz et al., 1986).Kondo et al. (2003) found significant differences in rooting characteristics, especially deep rooting depth and root biomass, among various (aerobic and upland) rice varieties.There are only few attempts to address the physiological responses of rice and critical analysis of various yield components to aerobic (Bouman, Peng, Castaneda, & Visperas, 2005) and drip irrigated condition.Poor root systems and root function limit water absorption and decrease in leaf water potential (Matso & Mochizuki, 2009) under aerobic cultivation.In the current scenario, drip irrigation offers a viable and alternate water-saving system for rice.
Pressurized irrigation systems have potential to increase water productivity by providing water to match crop requirements, reducing runoff, deep drainage losses, generally keeping soil drier reducing soil evaporation and increasing the capacity to capture rainfall.Karlberg, Rockstrom, Annandale, and Steyn (2007) reported that two low-cost drip irrigation systems with different emitter discharge rates were used to irrigate tomatoes and concluded that combination of drip systems with plastic mulch increased the yield.Application efficiency of different surface and pressurized irrigation methods varies and depends on design, management and operation (Holzapfel & Arumí, 2006).Ibragimov et al. (2007) compared drip and furrow irrigation in cotton and inferred that 18-42% of the irrigation water could be saved with drip systems with increased Irrigation Water Use Efficiency (35-103%) compared to furrow irrigation.
The drip irrigation treatment had more effective tillers, more roots in topsoil, higher WUE, and greater economic benefit in rice (He, Ma, Yang, Chen, & Jia, 2013), but less yield compare with conventional flooding irrigation.Drip irrigation maintained a competitive grain yield and water productivity, and greatly reduced pollution risk to the environment.Considering the conservative amount of fertilizer application, less than the amount of fertilization in normal paddy field, the yield potential of rice could be improved by increasing the amount of fertilizer as top application in drip irrigation system (Adekoya et al., 2014).
Considering the above, objectives of this experiment were set out to study the performance of rice, optimize the lateral distance and discharge rate for better grain yield, compare water requirements, water productivity, growth, physiological and yield responses in varied drip-irrigation treatments consisting of three lateral spacings with two levels of emitter discharge rate.

Method
The experiment was conducted during Dry Season (DS) of 2012 in the Wetlands of Tamil Nadu Agricultural University, Coimbatore, Tamil Nadu, India situated at 11 o N latitude, 77 o E longitude and at an altitude of 426.72 m above Mean Sea Level.Field experiment was taken in Randomized Block Design with three replications using ADT(R) 45 as the test variety.

Field Preparation
The experimental plots were dry-ploughed and harrowed.Raised flat beds were formed and laid out with double channels around all the plots to prevent subsoil lateral water flow.

Sowing and Spacing
Sprouted seeds (ADT (R) 45) were dry-sown by hand dibbling at 3cm depth in rows of 20 cm apart at seeding rate of 30 kg ha -1 .

Irrigation
The irrigation was given through PVC pipe (40 mm OD) after filtering through the screen filter by 7.5 HP motor from the bore well.The pressure maintained in the system was 1.2 Kg cm -2 .From the sub-main, in-line laterals were laid out at a spacing of 0.6, 0.8 or 1.0 m with 0.6 or 1.0 lph discharge rate emitters positioned at a distance of 30 cm.Irrigation was given based on the Open Pan Evaporation (PE) values (125% PE).

Treatment Details
There were eleven treatments employing three lateral spacings and two discharge rates of emitters.The treatments were: distance between laterals 0.6 m with the spacing of 20 cm between rows of plants and spacing of 10 cm between plants (T 1 ), distance between laterals 0.6m, spacing between rows of plants from lateral (20 × 10 × 10 × 20) (instead of three rows of 20 cm each) (T 2 ), lateral distance of 0.8 m, spacing of 20 cm between rows of plants and spacing of 10 cm between plants (T 3 ), lateral distance of 0.8 m, spacing between rows of plants from lateral (5 × 20 × 30 × 20 × 5) (instead of four rows of 20 cm each) (T 4 ), lateral distance of 1.0 m, spacing of 20 cm between rows of plants and spacing of 10 cm between plants (T 5 ), laterals distance of 1.0 m, spacing between rows of plants from lateral (7.5 × 15 × 15 × empty bed (25cm) × 15 × 15 × 7.5) (instead of five rows of 20 cm each) (T 6 ), laterals distance of 0.8 m, spacing of 20 cm between rows and spacing of 10 cm between plants + 30 percent more water (T 7 ), lateral distance of 1.0 m, spacing of 20 cm between rows of plants and spacing of 10 cm between plants + 30 percent more water (T 8 ), lateral distance of 0.8 m, spacing between rows of plants from lateral (5 × 20 × 30 × 20 × 5) (instead of four rows of 20 cm each) with 0.6 lph drippers (T 9 ), jas.ccsenet.lateral dist 15 × 7.5) ( ratio of 1.2

Weathe
The weath Agricultur temperatur with the to under drip 1974).After thrashing the grains, weight of the grain was taken.Grain yield per hectare was calculated from the mean plot yield and expressed in kg ha -1 at 14% moisture content.Water productivity was calculated as the weight of grains produced per unit of water input (irrigation and rainfall) as per the formula of Yang et al. (2005) and expressed as g grain kg -1 of water.

Research Design
The recorded data were subjected to statistical analysis in Randomized Block Design (RBD) using ANOVA Package (AGRES version 7.01) following the method of Gomez and Gomez (1984).
By comparing the T 1 (0.6 m LD), T 3 (0.8 m LD) and T 5 (1.0 m LD) treatments, increase in lateral distance caused reduction in water availability to the root zone of crop.Significantly higher dry matter was accumulated in treatment T 3 (1926.3g m -2 ) and the least in T 10 (1469.9g m -2 ).

Physiological Parameters
The physiological effects of aerobic rice on various micro irrigation treatments were analyzed and results were furnished below.The water potential is an indicator of plant water status under limited water supplying environment.Higher water potential ( w ) was observed in T 1 (-1.39MPa) and lower observed in T 11 (-1.87MPa) (Table 2).
Regarding the lipid peroxidation of leaf was observed by using leaf melondialdehyde content.Lesser leaf melondialdehyde content was recorded in the best treatment T 3 (38.6 µmol g -1 ) which is closer to the treatment T 1 and T 2 than the conventional aerobic rice treatment (T 11 : 48.6 µmol g -1 ).

Water Parameters
The total water applied to the crop through the irrigation water and effective rainfall for the entire growing season was 547 mm in T 1 , T 2 , T 3 , T 4 , T 5 , T 6 , T 9 and T 10 , 631.5 mm in T 7, T 8 and 697.9 mm in T 11 treatment (Table 4).The Water Productivity (WP) is a measure of the productivity of water used by the crop.Higher WP was recorded (Table 4) in T 3 (1.059g kg -1 ) followed by T 1 (1.015 g kg -1 ), T 4 (0.989 g kg -1 ) and T 2 (0.974 g kg -1 ).The least Water Productivity was observed in the conventional irrigation at IW/CPE ratio of 1.25 (T 11 ) (0.661 g kg -1 ).The Water Productivity (WP) is a measure of the productivity of water used by the crop.Higher WP was recorded (Table 4) in T 3 (1.059g kg -1 ) followed by T 1 (1.015 g kg -1 ), T 4 (0.989 g kg -1 ) and T 2 (0.974 g kg -1 ).The least WP was observed in the conventional irrigation at IW/CPE ratio of 1.25 (T 11 ) (0.661 g kg -1 ) (Table 4).

Discussion
Increased plant height observed in 0.8 LD, 1.0 lph dripper treatment (T 1 ) that was due to the availability of soil moisture to root zone in this system.This moderate plant height diverted all assimilates for growth with comparatively lesser share of assimilates available for shoot growth even under moisture limitation (Sangsu et al., 1999).Tillering is an important trait for grain production and is thereby an important aspect of rice growth improvement.The tiller density of the crop was significantly different in drip irrigation treatment.These results were obtained by more number of tillers per square meter due to more availability of nitrogen, which plays a vital role in cell division at tillering phase.Mirza, Ahamed, Rahmatullah, Akhter, and Rahman (2010)    mean saving of 21.6 percent of water when applied through the drip system than the conventional irrigation.Bouman et al. (2007) reported that the yields of aerobic rice obtained by farmers around North China Plain were 5.5 t ha -1 with sometimes as little as 566 mm of total water input, and with only one or two supplementary irrigation applications.Similar results were obtained in the present study also.
The Water Productivity values differed considerably among the treatments and generally tended to increase with a decline in irrigation (Howell, 2006).The water productivity was higher by 1.6 times in T 3 when compared to T 11 treatment with 54.4% reduction in water use (Figure 2).Our results are in accordance with the study of Guang-hui, Jun, Hua-qi, and Bouman, (2008) who reported 60% lesser water use coupled with 1.6-1.9times higher total water productivity in the present study.
Research findings of current study revealed that 1.0 lph drippers excelled 0.6 lph drippers in terms of growth characters, physiological parameters, water productivity, yield and its components.For the lateral distance treatments, 0.8 m lateral distance was found optimum lateral spacing due to better crop performance and yield than 1.0 m lateral distance.The treatment T 3 (lateral spacing of 0.8 m with 1.0 lph dripper discharge rate) registered superior performance in terms of growth indices (such as plant height, tiller density, root biomass, Total Dry Matter Accumulation), physiological parameters (such as  w , total chlorophyll, catalase activity and leaf malondialdehyde value), yield and its components along with increased WP values.Drip irrigation confirms to increase in water productivity in the present study with water saving of 27.4% over the conventional aerobic rice cultivation.Enhanced physiological activities showed increased growth and yield in rice under 0.8 m lateral distance drip irrigation which is a viable tool for balanced source sink relation.Our results indicated that the lateral spacing of 0.8 m with 1.0 lph drippers is best for rice cultivation in enhancing the growth, physiology, grain yield and water productivity.

Table 1 .
Effect of various drip irrigation treatments on Growth parameters of rice

Table 2 .
Effect of various drip irrigation treatments on physiological parameters of rice

Table 4 .
Effect of various micro irrigation treatments on water, yield of rice Note.IW: Irrigation water applied; ER: Effective Rainfall; TWA: Total Water Applied; GY: Grain Yield.