9 Agrichemical/Fertiliser Use Indicators
9.1 ISSUES
Agrichemicals and fertilisers are regularly used on farms to improve the soil health, and provide additional nutrients for plants. Essentially, they are a method of increasing productivity. Many agrichemicals and fertilisers, while increasing productivity and thus profit, have the potential to create adverse environmental effects. For example, the use of excess chemicals on the land, or application at the wrong time can result in washoff to surface waters, contamination of groundwater, or inefficient uptake by plants. Agrichemicals can produce spray drift, and reduce the biodiversity of plants and animals in the area. Chemicals and fertilisers are also expensive.
Fertigation and chemigation, where fertilisers or chemicals are applied through irrigation systems, are widely used in horticultural irrigation systems. In this case, indicators relating to efficient use of water (Section 10) have a direct relationship with fertiliser and chemical use. Any management decisions made by a farm to minimise water loss will also minimise chemical use and loss.
9.2 POTENTIAL INDICATORS
Irrigation influences the use of fertilisers and agrichemicals in several ways. The first is that the timing of irrigation events may be such that the chemical/fertiliser applied is washed away, or driven through the soil. Nitrogen, for example, is known to be leached out of soil quickly following rainfall or irrigation events. A second effect that irrigation has on fertiliser and agrichemical use is that it also increases production, and improves the soil quality, meaning that less chemicals may be required to achieve the same level of production. Particularly with wastewater irrigation, fertiliser application can be significantly reduced because of the nutrients applied to the soil with the wastewater. Indicators that can be used to address the problems associated with agrichemical and fertiliser use are:
- amount of agrichemical/ fertiliser used (kg/ha) for each crop;
- amount of residue in crops;
- concentration of chemical in drainage/surface water;
- cost of agrichemicals/fertiliser;
- production/unit chemical applied (t/kg).
9.3 RATIONALE FOR SELECTING INDICATORS
Since irrigation mainly affects the quantities of chemicals used, it is most important to keep track of the amounts of agrichemicals and fertilisers applied. As mentioned in Section 10, it is difficult to measure the quality of drainage water beneath the soil. Timing of applications of fertiliser and irrigation water certainly does affect drainage water quality. However, relating these factors individually to drainage water quality is almost impossible. Measuring the cost of the chemicals alone is not a suitable indicator, because it does not measure the increased production as a result of applying the chemicals.
In terms of wanting to reduce the amount of chemicals applied (an environmental as well as an economic goal), the quantity of fertilisers/agrichemicals used compared to the resulting production could be used as an indicator of the difference that irrigation makes to the amount of chemicals required. Additionally, it is a good idea to try to isolate the quantity of chemicals used for each crop, so that scheduling and application rates can be more exact - i.e. not over-fertilising particular crops, or applying the wrong type of agrichemicals.
9.4 RECOMMENDED INDICATOR
| Agrichemicals and fertilisers used per quantity of crop produced (kg/t or l/t per crop) |
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