Breadcrumb Links:

Oxygation

Oxygation is a method for enhancing the performance of   subsurface drip irrigation systems by adding air directly to the root   zone of crop plants to overcoming the negative effects of poor soil   aeration. Oxygation can enhance the yield and quality of crops,   particularly those grown on heavier soils. The Centre for Plant and   Water Science at CQUniversity, Australia is the world leader in   oxygation research.

The Centre for Plant and Water Science is involved in a   range of activities concerning oxygation. Research is being conducted to   improve the efficiency of existing oxygation systems, to perfect novel   oxygation systems and to and expand the application of oxygation to a   range of crop varieties and environmental conditions. CQUniversity   academic staff and postgraduate students are working in association with   research partners in a diverse range of organisations within Australia   and worldwide.

The Centre for Plant and Water Science welcomes   opportunities for collaboration from research organisations and   interested commercial ventures within Australia and worldwide.

Oxygation involves mixing atmospheric air with irrigation water using   a venturi and delivering it via a subsurface drip irrigation (SDI)   system. An oxygation system can be installed as part of a new SDI system   or may be readily 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 the   laterals and drip lines, or a single injector may be fitted to the   beginning of each drip line.

Oxygation improves water use efficiency (WUE), producing more yield   and greater profits from the water use. Oxygation can also reduce   problems associated with saline soils or saline irrigation water.    Oxygation is environmentally benign and economically cost-effective.   Water for irrigation is one of the most critical issues for the   sustainable primary industries in Australia.  Conventional irrigation   methods such as flood irrigation have large inefficiencies due to   run-off, drainage and losses in the irrigation. SDI can significantly   improve the WUE and yield of crop, and oxygation can significantly   improve SDI.

For more information on installing an oxygation system contact David Midmore at CQUniversity or visit the Mazzei Injector Company's website.

What is soil aeration?

Soil aeration relates to the ability of soils to exchange gases with   the atmosphere. This exchange is usually achieved primarily through   diffusion of gasses from and to the soil via pore spaces in the soil.    Soil aeration can be characterised as the gas-filled pore space in a   given volume of soil.

Why is aeration of the crop root zone essential?

 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

A lack of oxygen reduces the vigour of the root system and decreases   the depth of penetration of the roots.  This in turn reduces the soil   volume area from which the plant is capable of extracting water and   nutrients and limits plant growth even when water and minerals would not   appear to be limiting. If hypoxia persists for several days root   systems begin to die. If this occurs recovery may be slow even after   adequate aeration is provided.

  •  
  • Reduced ability of roots to absorb minerals and water from the soil

In poorly-aerated soil reduced root growth alone can have significant   effects on the ability of plants to absorb water and minerals. This is   exacerbated by reduced respiration which reduces the absorption of   nutrients, including nitrogen and phosphorous.  Plant roots lose their   ability to absorb water under conditions of hypoxia due to a number of   factors including a loss of root hairs and changes in the cell membrane   integrity.

  •  
  • Reduced plant growth due to stomatal closure

The reduction in water and mineral uptake that results from poor   aeration often causes stomata to close. This results in a marked   reduction in transpiration and photosynthesis and disrupts the hormonal   control of numerous plant systems and processes which leads to a   significant reduction in plant growth.

  •  
  • Loss of soil nitrogen due to the activity of microbes

A lack of oxygen in the soil reduces the rate of decomposition and   nitrogen mineralisation. Hypoxic conditions also increases the rate of   denitrification leading to a loss of nitrogen from the soil that may add   to atmospheric greenhouse gasses.  

  •  
  • Adverse changes in soil chemistry

A deficiency of oxygen results in a decrease in soil pH and redox   potential. These changes lead to the release of numerous chemicals which   are toxic to plants including methane, sulphides and reduced forms of   iron and manganese. The changes in pH and redox potential also alter the   availability of nutrients, aggravating the reducedability of roots to absorb minerals under hypoxic conditions.  

  •  
  • Increased susceptibility to disease

Root death and reduced root vigor increase the susceptibility of   plant roots to infection. A number of species of pathogenic fungi and   bacteria thrive in poorly aerated soil. As a result insufficient   aeration can increase attack by pathogenic soil microbes.

When is aeration a problem?

Insufficient aeration can occur under several circumstanes. For   example, large amounts of organic matter added to warm wet soils can   stimulate microbial activity to such an extent that soil oxygen is   depleted. Soil compaction can compress and reduce soil pore spaces and   reduce the ability of the soil to exchange oxygen with the atmosphere.   However, flooding or waterlogging are the most common conditions leading   to inadequate root aeration.

Waterlogging occurs when soil becomes saturated with water. If the   soil water content is too high, soil pores become blocked by water and   the ability of the soil to exchange gas with the atmosphere will be   greatly reduced or obstructed entirely. As a result soil oxygen will   decrease as it is consumed by plant roots, soil microbes and chemical   processes within the soil. If the soil is saturated for too long, all   the soil-based oxygen is used up. Heavy soils are most prone to   waterlogging due to their limited small pore spaces through which water   and air can only move slowly. Waterlogging may be the result of rainfall   or irrigation.

 When crops are flood-irrigated the root zone suffers periods of poor   aeration. The problem is exacerbated by more frequent irrigations or   longer irrigations, poor drainage or extended rainfall soon after an   irrigation. Furrow irrigation is also not water efficient and 40-50% of   water applied is lost through evaporation, runoff, and deep drainage.   There are also associated environmental impacts due to runoff and   percolation dispersing pesticides, fertilisers and other pollutants

 Subsurface Drip Irrigation (SDI) is one solution to the problems of   inefficient water use and pollutant dispersal and is a more efficient   and environmentally-friendly method of crop irrigation. In spite of the   documented benefits of SDI over furrow irrigation, rapid adoption is   still slow due to high capital investment and lack of significant yield   gain. Inadequate aeration is the most likely reason for the lack of   yield increase even at the optimum level of water application in an SDI   crop. Under SDI water is delivered over a longer duration than furrow   irrigation and directly into the active root zone, making parts of the   root zone almost saturated with water. As a result the root zone of SDI   irrigated crops, particularly in heavy and medium textured soils,   experiences episodic or continuous hypoxia. As drip irrigation develops a   wetting front near emitters as majority of the crop root zone remains   near-saturated for a proportion of the time between irrigation events.    SDI also minimises alternate wetting and drying of the soil surface, a   phenomenon that might otherwise predispose heavy clay soil to the   cracking that could locally alleviate the lack of aeration.

How can hypoxia be identified?

Hypoxia often causes lower leaves to become yellow, either in patches   or across the whole leaf, followed by premature death of the older   leaves. Uppermost leaves also tend to develop similar symptoms as   hypoxia continues. This is caused by the inability of plants to absorb   nitrogen from the soil, leading to remobilization from older leaves to   support the growth of new leaves.

How to overcome hypoxia.

In SDI systems one means of alleviating hypoxia is through the   introduction of oxygen directly to the root zone along with the water   supply. This may be achieved by the introduction of oxygen releasing   chemicals, such as hydrogen peroxide, into the irrigation water supply.   Another method is to utilise an in-line venturi to suck air into the   irrigation stream.

Hypoxia under both SDI and other irrigation systems can be dealt with in several additional ways:

  •  
  • Fertiliser should be applied immediately following waterlogging to   ensure that nutrients particularly nitrates, are readily available to   enable plants to recover.
  •  
  • Cropped areas should be kept free of weeds to reduce competition for oxygen in the root zone.
  •  
  • Permanent raised beds may be utilized to improve drainage.
  •  
  • Drainage may be improved by leveling the area and increasing the   density of drainage channels, to lower water tables following flooding.
  •  
  • Deep cultivation can increase soil pore space and break up hard pans that might have developed.
  •  
  • The addition of organic material into the soil may help to improve pore space within the soil.