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Improve water use of potatoes

As a result of their sensitivity to moisture stress, more than 80% of plantings in South Africa are currently irrigated. If one considers that close to 50 000 ha of potatoes are planted in this country, one cannot but realise that the potato industry is a major consumer of water.

To play an active part in a crop’s water use efficiency (WUE), there has to be a thorough understanding of how the crop functions and where gaps and opportunities exist. The average WUE of potatoes in South Africa is 80 kg/ha/mm. This varies drastically between regions due to:

  • Time of planting – a winter planting will not have the same high transpiration rate as in summer.
  • Rainfall – dryland plantings and plantings where the rainy season overlaps will need less additional water (from other sources).
  • Soil type – deep drained sandy soils cannot depend on water available in the profile and will therefore need more irrigation.
  • Cultivars – certain cultivars are more efficient in terms of their need for water.
  • Irrigation system – systems differ in their efficacy to limit water loss.
  • Management practices – certain management practices contribute to WUE.

Omnia is committed to its clients, but also to the environment and the sustainability of the agricultural sector in South Africa. Therefore, Omnia’s team of agronomists not only has a duty, but a responsibility regarding the WUE of potatoes.

Omnia’s agronomists are very excited about the WUE concept. We use many moisture models, meters, sensors and other technologies such as Greenseeker®, SPAD meters and OmniSap® in our WUE research. SPAD meters are used to measure the chlorophyll content of plants. Together with the Omnia norms, this can pinpoint the level of nitrogen (N) in the plant, which will lead to improved N management and more efficient plants. There is enough proof that N management has an enormous effect on WUE. OmniSap® analyses can be used to improve the management of all the nutrients and it can also determine the respective ammonium and nitrate content. Ammonium toxicity is one of the greatest culprits that negatively affects yield, especially under certain climatic conditions. Another benefit of OmniSap® is that it can accurately determine when to apply which plant nutrients if used with leaf samples continually throughout the growing season.

This reduces unnecessary application of especially micronutrients and is extremely useful to ensure that the plant would never experience any nutrient deficiencies in its growing cycle.

Precision farming is an important resource in the increase of WUE. Not only are the chemical grid analyses important, but also the soil type and therefore the yield potential of the soil. This is the core of precision farming. WUE is drastically improved when crops are planted in the right soil type. It also gives excellent information regarding the irrigation management of a field or zones in a field. Certain soil types also have the ability to give high yields with relatively little water, while other soil types can easily become waterlogged with a small amount of water.

The focus should not only be on one aspect of crop production, but on a holistic programme – from cultivar choice and soil preparation, to crop growth parameters and yield data. Omnia’s agronomists are exposed to a wealth of knowledge regarding everything that influences WUE to ensure that Omnia clients stay on the forefront of sustainability and the effective use of resources.

Omnia is also busy developing this technology at cultivar level. It is relatively well known that the nutrient and moisture requirements of every cultivar differ and it is therefore extremely important to consider these differences when a crop is planned and managed.

Several trials are being conducted to improve the use of nutrients and to better understand and determine how and when to apply them to increase the efficiency of potatoes (and therefore WUE). Preliminary trial results on silicon and plant hormones as foliar sprays seem promising, while OMNICAL(Ca) and
OMNI-K(K) trials have also yielded excellent results. During the initial pilot trials dramatic differences in quality have already been observed.

Figure 1 shows an increase in the Greenseeker® reading with increased K applications, while a difference can also be seen between the low and high Ca applications.

Greenseeker® is a device with optical sensors that measures crop growth and differences. The readings are used to apply different rates of top dressing in zones of different plant growth, or to make yield estimations. Calcium was applied during tuber initiation and potassium approximately 10 days later. Both were broadcast as granules. The potatoes experienced slight frost, and readings were taken after visual colour differences were observed. These results agree with other findings on the effect of potassium and calcium in the protection of membranes. This showed that the plants on the plots that received extra K and Ca applications were able to more effectively resist the stress condition.

Concerning the potato industry, Omnia’s team of agronomists is committed to giving producers access to all the necessary knowledge and resources to ensure that every resource is used optimally – both now and in the uncertain future.

By André Labuschagne
Agronomist - Free State Business Unit