Chemigation is the practice of applying chemical to a field through the irrigation system. As centre pivots and laterals apply water very evenly over the field compared to rain guns or stationary sprinklers, they are an ideal conduit for chemicals such as fertiliser, herbicide, fungicide and insecticide to be applied at very consistent rates. Not all chemicals are suitable for this purpose, but there are hundreds of brand-name pesticides and fertilisers from the US that are specifically registered for use via centre pivots.

Advantages of chemigation over boom-sprays mounted on tractors are:

*No need to book spraying contractors such as Meqanizatori

*No fuel costs.

*Only one operator needed

*No risk of a tractor accidentally damaging potato beds

*No risk of soil compaction due to a tractor operating on a wet field.

*Speed of operation and accuracy of application rate.

* Much less exposure of labour to chemical

Our fertigation mixers from INTA are ideally suited to this purpose, capable of injecting up to eight different chemicals in precise amounts into the irrigation main line, and capable of handling a wide range of fertilisers and pesticides.



Uniformity Tests and Placement of Soil Moisture Probes

Now that our plants have emerged, we are placing a number of Sentek EasyAg 50 soil moisture probes in our field. These are connected to Sentek Solo head units, which download information to a robust aluminium Soloporter data retrieval unit. We then download information on the previous day’s soil moisture readings, recorded every 15 minutes at 10, 20, 30, 40 and 50 cm depth into our Irrimax software, for analysis and scheduling of irrigation to meet the requirements of the potato plants.

In order to place probes in an area representative of the field regarding moisture, we must turn on the sprinklers on the pivot and collect water in cups to ensure that minor differences in discharge rate do not result in abnormally dry or wet patches into which a probe may be randomly inserted.



Finally, we insert the probes within a plastic casing in a proven representative area of the field, connect to a waterproof head unit, and download data at regular intervals. Rather than just observing plant turgor, or feeling soil moisture in our hands once a day subjectively, we have objective measurement of moisture four times an hour, allowing us to compensate for normal daily fluctuations in moisture over every 24 hour period and to accurately schedule irrigation frequency and amount over different soil types within the field.



Potato Planting

We planted approximately 7 Ha of potato last month, and received an additional 9 tonne of tubers recently, which we have planted on 3.2 Ha on the easterly aspect of the field. This part of the field is quite stony so we will have to harvest by hand.

The planter we use, a Grimme GL430, is fitted with potato cups on a belt capable of handling small and mid-sized tubers. Spacing between tubers in a row is controlled by changing two cogs in a chain drive on the left side of the planter, and dry fertiliser application rate is similarly controlled by a chain drive on the right side. Regardless of ground speed, application rate of seed and fertiliser per hectare remains constant.

Control of rhizoctonia fungus and wireworm (larvae of the click beetle that can cause damage to tubers) is done with a Bayer product, Prestige, applied by a pair of conical jets spraying a mist of seed dressing over tubers as they drop through the planter. By keeping ground speed relatively constant and controlling seed dressing concentration, we can deliver a consistent dose of dressing per tonne of tuber during the planting process.

This two-phase planter forms beds concurrently with planting; we adjust the bed formers to get a nice bed formed over the tubers, which we will re-form later in the season after the soil has settled.

Next week we are due to apply a pre-emergent herbicide, metribuzin, to this part of the field by spray rig. Stay tuned.