The physiology of water use efficiency of crops subjected to subsurface drip irrigation, oxygation and salinity in a heavy clay soil

Furrow is the dominant irrigation method for agriculture throughout the world. However, due to water use inefficiencies, only about 50% of the water that reaches the field is used by the crop, the remainder at times negatively impacting the environment. This research explored the potential of subsurface drip irrigation (SDI) to raise water use efficiency (WUE) of cotton produced on a heavy clay soil, and to minimize the negative environmental impact of irrigation water. SDI cotton irrigated at the rate of 75 % daily crop evapo-transpirational demand (ETc) produced yield equivalent to, or greater than, that with SDI at 120/105 ETc in both seasons in Emerald, Queensland. Lint yield of SDI 75% ETc was comparable to the conventional furrow method in 2001/02 season and less by 18% in 2002/03 season, but used only approximately half of the water input (52%). The SDI crop irrigated at 50% ETc showed enhanced crop earliness and WUE, but had lower lint yield, whereas higher SDI irrigation levels (> 90% ETc) delayed crop maturity without benefits for yield or WUE. Furrow registered the highest drainage and runoff over the two seasons (114 mm and 224 mm) compared with the SDI at 105/120 ETc (65 mm and 32 mm) whereas SDI 90% ETc had no runoff but leakage of 17 mm and neither drainage nor runoff were observed at SDI at 50 and 75% ETc. It was hypothesized that at higher irrigation rates, SDI crops experience lack of oxygen in the root zone, which becomes a limiting factor for improving WUE at higher irrigation rates at and above 90% ETc for cotton in heavy clay soil. The potential of subsurface oxygation (irrigating oxygen-rich water to plants through drip tape- the details about oxygation approach, mechanism and terminology are presented in Bhattarai et al., 2005c) using aerated irrigation water (mixing 12% air by volume of water using Mazzei model venturi for in-line air injection) or hydrogen peroxide solution (at 0.5 ml H2O2 L-1 of irrigation water throughout the irrigation cycle) viii was therefore investigated at a range of soil moisture levels in the glasshouse, screenhouse and outside at Rockhampton, Queensland. Following irrigation events soil O2 declined by 45% in non-aerated plots while in aerated plots soil O2 decreased by only 25%. Oxygen measurements in the rhizosphere over a 72-hour period during the flowering stage revealed greater oxygen concentration with aerated treatments compared with the control at both field capacity (8.1 vs 7.1 mg L-1) and deficit (9.2 vs 8.1 mg L-1) soil moisture conditions. Yield was increased on average by 86, 20 and 21% for soybean, cotton and tomato, respectively, due to aeration across soil moisture levels and types of aeration. Such increase in yield was associated with greater number of pods for soybean, bolls and their individual weight for cotton and fruit size in tomato. Aeration treatments also increased water use by plants and were associated with greater WUE in all experiments. The effect of aeration was significant on the rate of net photosynthesis per unit leaf area when pots were aerated, but instantaneous leaf stomatal conductance and unit leaf transpiration rates were not affected. However, higher stem sap flow rates indicated greater canopy transpiration over longer time intervals in aerated treatments. Higher root weight and soil respiration were observed in aerated treatments compared with the control. Hence, aeration-induced root functioning was arguably responsible for greater fruit set and yield in all three crops, while in vegetable soybean greater canopy interception of radiation and greater total vegetative biomass were also responsible for additional yield benefits, and in tomato the effect was due to higher leaf area, chlorophyll content, and bigger fruit. Salinity is a major environmental threat in many parts of the world. Salinity in clay soils is often associated with sodicity, which reduces the porosity in the soil thereby reducing soil oxygen concentration. The effect of oxygation (with aerated water) for SDI crops in a range of salinities (tomato: 2.0, 4.0, 8.6,10.0; cotton and ix soybean: 2.0, 8.0, 14.0, 20.0 dS m-1 ECe) in heavy clay soils was valuated. Oxygation on average increased yield of tomato, vegetable soybean and cotton by 38, 12 and 18 percent respectively, but yields decreased significantly with increasing salinity levels. Aeration of saline soil increased WUE for fruit and biomass in all three species but not the instantaneous WUE, measured as Somol CO2 fixed per mmol H2O transpired, with the exception of cotton. Aeration increased, and salinity decreased, cumulative transpiration as determined by stem sap flow over a two week period during flowering in vegetable soybean. Plants in aerated treatments showed increased stem diameter, improved membrane permeability expressed by reduced relative leakage ratio and possibly enhanced ion regulation as revealed by greater sodium exclusion and intact root membrane as revealed in the TS of aerated roots in the saline soils. The increase in yield in tomato and cotton was also accompanied by increased harvest index, greater fruit size, higher fruit number, shoot: root ratio, and lower water stress index. The rate of net leaf photosynthesis increased with aeration and decreased with salinity in cotton and soybean; however, in tomato the aeration effect on photosynthesis was not significant although salinity did significantly reduce net leaf photosynthesis. Aeration improved selective membrane permeability as evidenced by reduced lectrolyte leakage. Hence it is suggested that aeration helps exclude the ingress of salts into the plants and increases uptake of water and nutrients for growth in saline environments. Evidence from these controlled environment experiments warrants the commercial-scale testing of the oxygation technology for application to the agricultural and horticultural industries especially to add value to growers investments in SDI and to diminish potential negative impacts of over-use of irrigation water

Oxygation of rhizosphere with subsurface aerated irrigation water improves lint yield and performance of cotton on saline heavy clay soil

Salinity in agricultural soils has large impact on plant performance. Waterlogging and anoxia due to poor soil structure is a major problem for crop production in saline heavy clay soils. Inadequate oxygen concentration in the rhizosphere exacerbates the effect of salt and leads to poor plant performance. An experiment in the screen house was conducted to investigate growth and yield performance of cotton (Gossypium hirsutum L.) supplied with subsurface aerated water or non-aerated water to soil with four different salinity (ECe) levels of 2, 8, 14, 20 dS/m. The interaction between salinity and aeration was found to be non-significant for the variables measured. Cotton produced a significantly higher dry matter and lint yield with aerated water, irrespective of soil salinity level. The increase in yield was accompanied by an increase in root mass, canopy light interception and harvest index

Oxygation : optimising delivery and benefits of aerated irrigation water.

Increasing competition on supply of fresh water for irrigation by agricultural, domestic, sports and industrial users demands water use efficient irrigation methods and compliancewith environmental regulations. Drip irrigation (DI) and subsurface drip irrigation (SDI) areadvocated for improvements in water use efficiency (WUE) and are increasingly beingadopted by horticultural industries in Australia and overseas. Greater flexibility for automation and versatility of application of drip irrigation technology encourage wider-scale adoption by these industries. However, the higher initial investment for installation and lack of significant yield gains due to drip irrigation compared to conventional irrigation methods are somehow deterrents for broad-scale adoption. Ways to optimise the use of DI and SDI will have multiplier effects on water savings for irrigation in agricultural and other industries and minimize environmental impacts associated with traditional irrigation methods. One of the significant areas where greater optimization of DI and SDI is realized is through the use of aerated water for irrigation (oxygation). Sustained wetting fronts around emitters associated with DI/SSDI impose hypoxia in the rhizosphere. This impedes root respiration leading to sub-optimal plant performance. As irrigation water exits an emitter, it purges soil pores of soil air (containing up to 20% by volume of oxygen) with water that contains less than 10 ppm oxygen, aquantity we have shown is used up quickly by roots and soil microbes. Rising soil temperatures, salinity, and soil compaction will exacerbate this effect, as may disease such as Phytophthora of pineapple. Plant roots and soil microbes require oxygen for respiration. In soils with inadequate aeration the lack of oxygen results in reduced plant growth and diminished productivity for many reasons, including: reduced root growth and root size; reduced root ability to absorb minerals and water; reduced photosynthesis and plant growth due to stomatal closure; loss of soil N due to the in-activity of microbes; adverse changes in soil chemistry; increased susceptibility to disease, and an alteration of the balance and supply of plant growth regulators. Aeration of the irrigation stream, a process termed ‘oxygation’, overcomes this constraint. Oxygation is a new innovation in irrigation technologies. Aerated DI and SDI by different methods, such as venturi for air injection, allows for the simultaneous application of water, air and other agro-chemicals directly to the crop root zone. Therefore, it can potentially improve crop yield and water use efficiency. Conventional irrigation methods such as flood irrigation have large inefficiencies due to run-off, drainage and evaporative loss. SDI cansignificantly improve the WUE over that of flood irrigation, and oxygation can significantly improve WUE of SDI. Oxygation involves mixing air with water using a venturi and delivering via a surface orsubsurface drip irrigation system. An oxygation system can be installed as part of a new SDI system or may be retrospectively fitted to any existing SDI system. A venturi air injector is installed within the pipeline and draws air directly into the water stream. A single venturi can be installed immediately after the pump outlet and the air distributed through the main line to sub mains and lateral drip lines, or a single injector may be fitted to the beginning of each drip line. The amount of air ingress depends on the pressure differential across the venturi and the motive flow through the venturi

Utilising organic wastes and alternative sources of plant nutrients for sustainable agriculture in Nepal

Subsistence oriented traditional agricultural practices in Nepal largely follow conventional approaches for soil fertility management. Conventional methods for soil fertility management rely primarily on use of compost and farmyard manure (FYM) as the main sources of plant nutrients. Recently, a shift from subsistence to semi-commercial production systems required changes in soil fertility management practices, which involved indiscriminate use of inorganic fertilisers, a decreasing trend of FYM and compost availability, and increasing use of poultry manure for crop production. More recent trends of commercial farming include crop intensification, use of high yielding varieties and specialised farming e.g. commercial vegetable and cash crops production. These are nutrient hungry production systems and currently dependent solely on inorganic fertilisers. Excessive nutrients depletion by these intensive production systems imposes severe consequences for soil fertility management, including increasing, and degradation of chemical, biological and physical properties of soil leading to loss of overall soil fertility and the appearance of severe micronutrients deficiencies in a number of crops. A far reaching and sustainable approach includes building integrated soil fertility management together with the use of under-utilised sources of plant nutrients such as bio-fertiliser technologies and recycling of organic residues, and enhanced composting (such as vermi-composting). Manufacturing of fertiliser products (granules, pellets, briquettes) from plant, animal and human wastes, and optimising the use of these products as alternative fertilisers are needed. The economic and environmental benefits from these products can be harnessed for sustainable production of crops, without jeopardising soil fertility and the environment. Achieving this result should be considered a priority goal for sustainable agriculture. This paper describes the scope of the alternative sources of plant nutrient management and their production and scaling-up for a wider adaptation in Nepal

Oxygation enhances growth, gas exchange and salt tolerance of vegetable soybean and cotton in a saline vertisol

Impacts of salinity become severe when the soil is deficient in oxygen. Oxygation (using aerated water for subsurface drip irrigation of crop) could minimize the impact of salinity on plants under oxygen-limiting soil environments. Pot experiments were conducted to evaluate the effects of oxygation (12% air volume/volume of water) on vegetable soybean (moderately salt tolerant) and cotton (salt tolerant) in a salinized vertisol at 2, 8, 14, 20 dS/m ECe. In vegetable soybean, oxygation increased above ground biomass yield and water use efficiency (WUE) by 13% and 22%, respectively, compared with the control. Higher yield with oxygation was accompanied by greater plant height and stem diameter and reduced specific leaf area and leaf Na+ and Cl− concentrations. In cotton, oxygation increased lint yield and WUE by 18% and 16%, respectively,compared with the control, and was accompanied by greater canopy light interception, plant height and stem diameter. Oxygation also led to a greater rate of photosynthesis, higher relative water content in the leaf, reduced crop water stress index and lower leaf water potential. It did not, however, affect leaf Na+ or Cl− concentration. Oxygation invariably increased,whereas salinity reduced the K+ : Na+ ratio in the leaves of both species. Oxygation improved yield and WUE performanceof salt tolerant and moderately tolerant crops under saline soil environments, and this may have a significant impact for irrigated agriculture where saline soils pose constraints to crop production

Influence of soil moisture on yield and quality of tomato on a heavy clay soil

The effect of three soil moisture regimes [deficit: 22-26mm H2O per 100 mm soil depth, field capacity (FC): 34-43 mm and saturation: 44-48 mm] on growth, yield and quality of a tomato (Lycopersicon esculentum L. Mill) cultivar ‘Improved Apollo’ was examined on a heavy clay soil. Leaf area and plant height were reduced in deficit and saturation, whereas stem diameter increased with increasing soil moisture. Fruit yield declined by 31 and 24% in deficit and saturation respectively compared with the FC. Maximum attainable fruit yield would be achieved with 35 mm H2O per 100 mm soil depth. Total titratable acidity (TTA), ascorbic acid (AA) and firmness decreased and pH increased with increasing soil moisture. Dry matter, total soluble solids (TSS), TSS: TTA and blossom end rot (BER) were highest for deficit, followed by saturation and lowest at FC. Although yield increased and BER decreased at FC, other quality improved with water stress compared to FC

Carbon isotope discrimination and surrogates of water use efficiency for tomato under various soil moistures

Carbon isotope discrimination (Δ‰) is negatively correlated with water use efficiency (WUE) in several C3 species and was proposed as a selection criterion for improved WUE. Tomato (Lycopersion esculentum L.) cv. Improved Apollo, was exposed to soil moisture levels, saturated, field capacity (FC) and deficit soil moisture conditions, in a container experiment in a screenhouse. The objective was to test for: (1) difference between soil moisture levels as they affect water use efficiency, boimass production, and distribution; (2) evaluate the relationship between various measures of WUE and carbon isotope discrimination (Δ‰), between biomass production and Δ‰, and between stem diameter (SD) and WUE and, the use of SD as an alternate surrogate; and (3) discern the physiological processes associated with changes in WUE and Δ‰ with respect to different soil moisture levels in a heavy clay soil. Tomato plants responses were quantified in terms of biomass and fresh fruit yield, plant morphology, leaf gas exchange properties, WUE of biomass, and fruit, as well as Δ‰ by leaves. While number of leaves and nodes, and leaf area were least in the saturated treatment and greatest at FC; stem diameter at harvest was greatest under saturated conditions. Stem diameter was positively correlated with Δ‰, indicating the possibility of using stem diameter as a surrogate of WUE based upon dry weight of biomass or fruit, and for negative relationships between Δ‰. Midday leaf water potential and relative water content decreased with increasing moisture stress (deficit or saturated conditions). However, leaf chlorophyll concentration decreased as soil moisture content increased from deficit to FC to saturated. Fresh fruit yield was significantly greater at FC (4.476 kg/plant) compared with saturated (2.617 kg) and deficit (1.985 kg) treatments, as a result of greater mean weight/fruit rather than more fruit/plant. As fresh fruit yield and dry matter content of fruit were negatively related, the WUE of fresh fruit was not inversely related to Δ‰. The data indicate that in tomato, where marketable yield consists of fresh produce, the established negative relationship between WUE and Δ‰ does not hold true, and benefits of using Δ‰ as a surrogate for fresh yield WUE may not be effective while the strong negative correlation between SD and WUE suggests possibility of employing SD as surrogate of WUE

Potential benefits of oxygation-aeration of irrigation water to the Australian fruit industry

This article presents data on the global and Australian fruit industries, their water usage, and a newly researched option – oxygation – that considerably improves water use efficiency and quality of agricultural and horticultural produce

Effect of oxygation with respect to dripper depths on yield and water use efficiencies of soybean and pumpkin in vertisols

The purpose of the current study was to compare the role of oxygation on shallow vs deep delivery of subsurface drip irrigation on the root distribution, yield, water use efficiency and physiological response of vegetable soybean and pumpkin. The knowledge of rooting pattern is essential to irrigation and fertilizer management and consequently to achieving greater yield and quality. The objective of the study was to compare the effect of oxygation with respect to drip tape depth on soybean (at 5, 15, 25, and 35 cm) and pumpkin (at 5 and 15 cm) under controlled and field situation respectively. Plant response to drip depth with respect to oxygation, was studied in a temperature controlled environment (with vegetable soybean) and on a field scale cotnmercial level (pumpkin)

Evaluation of aerated subsurface drip irrigation on yield, dry weight partitioning and water use efficiency of a broad-acre chickpea (Cicer arietinum, L.) in a vertosol

Chickpea is susceptible to water logging and responds to soil aeration. Oxygen deficiency at both a temporal and spatial scale could occur for a subsurface drip irrigated crop, particularly in heavy clay soils. Use of aerated water irrigation (oxygation) to overcome hypoxia in the rhizosphere was evaluated in broad-acre chickpea crops in 2006 and 2007, in a heavy clay soil of central Queensland, Australia. The injection of 12% by volume air into subsurface drip irrigation water (oxygation) to two consecutive broad-acre chickpea crops resulted in a beneficial effect on yield (gains of 27% and 10% for 2006 and 2007, respectively), but the effect of irrigation regimes at deficit and full irrigation (85 and 100% ETc) was not significantly different. Chickpea yield with aerated subsurface drip irrigation was much higher (3.24 and 2.05 t ha -1 ) compared to the 7-year (2008–2015) national average yield (1.13 t ha -1 ). The aerated irrigation resulted into significantly higher gross production water use index (GPWUI) and irrigation water use index (IWUI) particularly in the year when the crop was planted early in the season. There was no significant difference in response to either of these water use efficiency (WUE) indicators between irrigation treatments, with the exception of a significantly enhanced IWUI with the 85% ETc in the first season. These results were consistent with those for cotton on the same site, providing further justification for the capital investment required for oxygated subsurface drip irrigation (SDI) system. © 2019 Elsevier B.V