P.S. Minhas

Saline water management for irrigation in India

Much (32–84%) of the ground water surveyed in different Indian States is rated either saline or alkali. Because of the continental monsoonal climate, the basic principles of saline water management need some adaptation, e.g. providing for a leaching requirement is not appropriate when the growing season for post-monsoon winter crops starts with a surface-leached soil profile, because it would increase the salt load. High salinities during the initial stages of growth are particularly harmful. Further, if benefits are to be gained from frequent saline irrigation, the amount of water applied per irrigation needs to be reduced. This is not possible with most widely practiced surface irrigation methods, but can be achieved with sprinkler and drip methods. However, in India the large-scale use of such systems is not yet technically or economically feasible. Another management goal is simultaneously to encourage the utilisation of carried over rainwater in the soil profile/shallow watertables. Tolerance limits of crops to the use of saline water in different agro-ecological regions of India are available, and have been observed to vary with soil type, rainfall and anionic/cationic constituents of salinity. Multi-location trials on the appropriate use of saline and non-saline water reveal the benefits of irrigating with non-saline canal water during the initial stages of growth, as well as cycles of saline and non-saline water during the pre-sowing irrigation period. Monsoon-induced salt leaching decreases with increasing clay content, SARiw, and is enhanced with increasing chloride salinity. Additional doses of phosphorous to alleviate the effects of chloride toxicity, and the use of organic materials to enhance the efficiency of applied nitrogen are recommended under saline-irrigated conditions. Contrary to the general belief that soils irrigated with high-SAR saline water may regain their infiltration capacity when the electrolytic concentration of ingoing water is greater than the flocculation value, irreversible reductions are induced under cyclic saline-rainwater infiltration where sub-soil layers, ingressed with clays from the plough layer, control steady intake rates. Thus, the use of gypsum (SARiw > 20) is advocated. Gypsum is also needed for soils irrigated with saline water with an Mg:Ca ratio > 3 and rich in silica. Other cultural practices, such as furrow planting, increasing the plant density and post-seeding irrigation in crops like mustard, also prove useful. Water-quality standards which were too conservative have been replaced by site-specific guidelines where factors such as soil texture, rainfall and crop tolerance have been given due consideration.

Conjunctive use of saline and non-saline waters. II. Field comparisions of cyclic uses and mixing for wheat

Abstract To evaluate the changes in soil water and salinity when conjunctive irrigation with canal (CW, 0.6 dS/m) and saline (SW, 12 dS/m) waters is practised in various cyclic/mixing modes and their associated effects on growth and yield of wheat, field experiments were conducted during 1989–1991 on a sandy loam soil. Normalising the treatment receiving canal water (100%), relative yield with saline irrigation was reduced to 60%. Substitution of canal water for saline water at pre-sowing stage improved seedling establishment and at first post-planting irrigation further enhanced tillering and related growth parameters, thereby, resulting in yield improvements by 18 and 16% over saline irrigation alone, respectively. Whereas cyclic irrigations with canal and saline water in 1 CW:1 SW and 2 CW:2 SW modes produced 7–11% more yields when compared with mixing in equal proportions (86%), yield was reduced by 12% in 1 SW:1 CW mode, i.e. using saline water to start with. Use of canal water at the initial stages seemed to cause priming effect through increased soil water depletion, thus resulting in better growth rates (tillering) whereas adjustment to reduced salinity stress at later stages via increased grains/ear failed to totally compensate for losses due to reduced tillering. Stepwise linear response function with time averaged salinity (ECe, dS/m) down to 1.2 m could be represented as: RY = 100 − 9.2 (ECe - 4.0). Multiple regression with dummy variables predicted EC50 (ECe for 50% yields) values to be 9.7, 11.9 and 16.7 dS/m, respectively, for salinity (0-0.3 m soil depth) at sowing, mid-season and harvest time indicating towards enhanced tolerance with ageing. It was concluded when making conjunctive use of canal and saline waters for the production of wheat, that higher efficiency of irrigation can be achieved with their cyclic use when canal water is applied at the initial stages (pre-irrigation and/first post-sowing irrigation) and saline water is used at the later growth periods when it can tolerate the salts better.

Effect of high salinity and SAR waters on salinization, sodication and yields of pearl-millet and wheat

Abstract A characteristic feature of saline ground waters is an increase in their sodium adsorption ratio, SAR with salinity. Besides salinity, irrigation with such waters leads to sodium saturation of soils which may lead to reduced infiltration. A field experiment was conducted from 1983 to 1989 to study the effects of irrigation with saline waters having combinations of electrical conductivity, ECiw (6 and 12 dS/m) and SARiw (5, 10, 20, 30 and 40 ( mmol / l ) 1 2 ) on properties of a sandy loam soil and yields of pearl-millet and wheat grown in rotation. Production functions fitted to predict relative yields (RY) could be represented for pearl-millet as: RY (%) = 133.1−ECiw (5.58−0.0026 R)−SARiw (0.0025 R + 0.43T)−0.03 (SARiw)2; R 2 = 0.79∗∗ and for Wheat as: RY (%) = 98.14−0.54 ECiw−SARiw (0.10 ECiw + 0.09T)−0.01 (SARiw)2; R 2 = 0.95∗∗ where R and T denote rainfall (mm) and time period after initiation of irrigation (years). Adverse effect of increased SARiw was greater on pearl-millet grown during monsoon rains. Increase in SAR of waters lead to increased build up of sodicity and salinity in soils, effects being more pronounced at ECiw 12 than 6 dS/m. Irrigation with waters having SAR of 20 and 40 (mmol/l) 1 2 reduced infiltration rates to 12 and 7% of the original soil, respectively. Monsoon rains leached a major portion of the salts added with irrigations to wheat, but the soils being irrigated with higher SAR (> 20) waters retained more salts. A leaching test confirmed reduced leaching efficiency of soils irrigated with high SAR waters as the depth of water required per unit depth of soil ( D w D s ) for displacing 75% of the salts averaged to 0.64, 0.82 and 0.89 m/m in soils irrigated with SAR iw = 5, 20, 40 ( mmol / l ) 1 2 , respectively. Amending the soil with gypsum @ 2 t ha before leaching increased the infiltration rate and salt displacement in soils irrigated with high SAR waters.

Conjunctive use of saline and non-saline waters. I: Response of wheat to initial salinity profiles and salinisation patterns

Abstract Response of wheat (Triticum aestivum L.) to salinity stress at different growth stages and patterns of salinisation was studied in microlysimeters. The treatments consisted of variable initial salinity profiles (salinity increasing, decreasing and uniform with depth) in combination with different salinisation patterns achieved through irrigations with waters of increasing, constant, decreasing salinity, alternating saline and non-saline, introducing saline waters after jointing, keeping the total salt input through these irrigations the same. Almost 3-fold variations in wheat yields were observed. In soil where initial salinity increased with soil depth, yields were markedly improved (30–36%) compared with the soils having uniform or inverted salt profiles. Similarly, shifting to saline irrigation at jointing, cyclically non-saline/saline water or increasing salinity, outyielded the others. Interestingly, lowest yields were obtained in soils receiving constant salinity waters. Amongst the various indices of salinity, yields were best related (r = −0.78) to root length weighted salinity over different periods of growth. Independent estimates of salinity responses showed the tolerance of wheat to increase with ontogeny. The EC50 values (electrical conductivity of saturation paste extract for 50% yields) increased to 9.3, 10.8 ± 0.1, 12.7 and 13.2 dS/m for periods between sowing to crown rooting, crown rooting to boot, boot to dough and dough stage to maturity, respectively. Results imply that for nonsteady state conditions such as those prevailing under monsoonal climate, the salt tolerance at critical stages of crop plants, changes in responses to salinity with modes of salinisation and initial distribution of salts need to be considered for effective use of multisalinity waters.

Conjunctive use of saline and non-saline waters. III. Validation and applications of a transient model for wheat

Abstract A transient state model for numerical simulations of water and solute transport and plant water uptake (V-H model) was modified and applied to develop saline irrigation strategies for wheat grown in Northern parts of India. Three modifications made in the sink term were: (1) allowing for increased tolerances to salinity stress at progressive growth stages of wheat; (2) time and depth patterns of root distribution as fitted to experimental data, i.e. a logistic function for rooting depth with time and an exponential function to define root distribution; and (3) reductions in osmotic stress due to ion pair formations on concentration of soil solutions with water uptake. With these modifications, the V-H model allowed for good agreement between observed and predicted wheat yields under various conjunctive use modes of saline and non-saline water (mean square error, MSE = 0.0027) as well as quantities and salinities of irrigation water over the years varying in rainfall (MSE = 0.0074). Production functions for different salinity waters and their quantities are also presented. Simulations indicated higher benefits of increasing frequency with saline irrigations when the quantity of water applied for each irrigation is simultaneously reduced. Otherwise, such a practice was predicted to increase salt load in soils, thus negating the benefits through aggrevated salinity. Potentialities of using higher salinity waters for wheat production increased when such waters were introduced late in the season.

Solute displacement in a silt loam soil as affected by the method of water application under different evaporation rates

Abstract To study the displacement and redistribution of surface applied salts as affected by continuous and intermittent ponding, three separate experiments were conducted on a silt loam soil during periods of varying atmospheric evaporativity. The USWB class A pan values during the successive study periods averaged 1.52, 7.74 and 4.51 mm/day and a total of 15, 22.5 and 40 cm water was used for leaching, respectively. In the case of intermittent ponding, water was applied at 10-day intervals in equal splits of 7.5 or 10 cm depth. No difference in leaching of chloride was observed when the same amount of water was applied continuously or intermittently during the periods of high (7.74 mm/day) and medium (4.51 mm/day) evaporation rates. However, when evaporation at the surface was prevented or remained low (1.52 mm/day), distinctly greater amounts of chloride were removed from the soil and the salt peak was displaced deeper under intermittent as compared to continuous ponding. Preferential movement of water through macropores in relation to micropores during leaching resulted in low mobility of surface applied chloride relative to that of water.

Field determined hydraulic properties of a sandy loam soil irrigated with various salinity and SAR waters

Changes in the infiltration, drainage, soil-water characteristics and unsaturated hydraulic conductivity were evaluated in field plots of a sandy loam soil irrigated with waters of different salinities (ECw 6 and 12 dS·m−1) and sodium adsorption ratios [SARw 5, 20 and 40 (mmol.·1−1)12] for a period of 8 years. Unsaturated hydraulic conductivity, K(θ), for the various treatments was determined by measuring hydraulic gradients and soil-water contents from simultaneously evaporating and draining profiles, as well as from draining profiles with no evaporation. Relative infiltration rate (RIR) was calculated considering steady infiltration in the original soil (22.5 mm·h−1) as the reference relationship. When measured using canal water (ECw 0.7 dS·m−1), RIRs were reduced to 0.64–0.90, 0.10 and 0.05–0.07 in soils irrigated with SARw 5, 20 and 40, respectively. Long-term use of higher salinity waters but with similar SARs caused greater deterioration. When waters of various salinities and SARs were used for measuring infiltration, the RIRs at SARw 5, 20 and 40 (mmol·1−1)12 were increased to 0.96, 0.79 and 0.42 in soils irrigated with ECw 6 dS·m−1. Likewise, RIRs were increased to 0.67, 0.35 and 0.27 for an ECw of 12 dS·m−1. Stability of the surface soil and thus permeability should have improved during infiltration of saline waters with electrolytic concentrations more than the flocculation values, but the small improvement in infiltration rates indicate that deeper soil controls the steady infiltration rate. The dispersed state of the deeper layers in soils irrigated with high SAR waters was further evident from increased soil-water retention at lower matric potentials in the tensiometric range, as well as being reflected in decreased values of drainage coefficients and increased soil-water storage. Unsaturated hydraulic conductivity K(θ), could be adequately described (r = 0.87–0.97) by the equation K = α exp·(βθ). Values of K(θ), when referenced to the original soil, ranged between 0.56 and 1.12 at θ = 0.3 but were reduced 2- and 4-fold at θ = 0.1 m3·m−3 for soils irrigated with waters of SARw = 20 and 40 (mmol·1−1)12, respectively. Results indicate that the laboratory determinations may not assess adequately the changes in hydraulic properties upon irrigation with high-SAR saline waters in soils undergoing cycles of salinization and desalinisation under a continental monsoon climate.

Response of wheat to irrigation with saline water varying in anionic constituents and phosphorus application

Abstract Most underground saline water is characterized by the predominance of either the SO2−4 or Cl− ions. Toxicity of chloride has been reported but how the ionic constituents effect the crop response to added phosphatic fertilizers is not known. This field study investigated the interactive effects of: salinity (80 and 120 meq/1), anionic constituents (Cl : SO4 ratios of 3 : 1, 1 : 1 and 1 : 3) and phosphatic fertilization (0, 26 and 39 kg P/ha) on salinization and sodication of soil and response of wheat. Average yields of wheat grown for 3 y in wheat-fallow rotation showed reductions of 4.7 and 12.5% at irrigation water electrolyte content (ECiw) of 6.1-6.7 and 8.8-9.9 dS/m, respectively. Increasing Cl : SO4 ratio in saline water to 1 : 1 and 3 : 1 reduced the grain yield by 5.9 and 11.6 percent, respectively when compared with yield obtained at Cl : SO4 ratio of 1 : 3. Phosphorus application (26 and 39 kg/ha) improved yield by 39 and 55 percent, respectively. A regression model used to describe the production function revealed that wheat yields could be sustained with higher salinity water if the Cl : SO4 ratio is lowered and/or with the application of additional phosphorus. Salt leaching due to monsoon rains was reduced in soils irrigated with SO4-dominant water. The SO2−4 associated cations were Na+ and Ca2+ + Mg2+ and higher SARe was maintained in lower soil layers. The amount of rain during monsoons influenced the patterns of sodication in soils irrigated with saline water varying in Cl : SO4 ratio.

Evaluation of Sowing Methods, Irrigation Schedules, Chemical Fertilizer Doses and Varieties of Plantago ovata Forsk. to Rehabilitate Degraded Calcareous Lands Irrigated with Saline Water in Dry Regions of Northwestern India

To get best economic returns from the degraded calcareous soils, which otherwise remain barren in arid and semi-arid regions of northwestern India due to non-availability of good quality water for irrigation, experiments were conducted for three years cultivating Plantago ovata Forsk. using saline water for irrigation on sandy loam soil. Six different sowing methods were compared, irrigating with saline water of electrical conductivity of 8.6 dS m−1. The yield was better when seeds were sown in dry soil followed by saline irrigation in comparison to when sown in moist soil created by pre-sowing irrigation with saline water. When different frequencies of irrigation were compared using water of low salinity (ECiw 4.0 dS m−1), high salinity (EC 8.6 dS m−1), and providing irrigation with waters of low and high salinity alternately, the average un-husked seed yield was found to be 1102, 885, and 1159 kg ha−1, respectively, showing significant advantage when the crop was irrigated alternately with water of low and high salinity. There was increase in yield with increase of frequency of irrigation. Experimentation with different doses of nitrogen and phosphorus fertilizers found that the yield was optimum during first year at 25 kg ha−1 and 50 kg ha−1 during second year. There was an increase in yield when increasing the dose of phosphorus, and there was a significant interaction between nitrogen and phosphorus application. Among eight varieties the best performance was shown by variety JI-4 followed by Sel-10, Niharika, HI-5, GI-2, GI-1, local, and HI-34, in descending order.