What fertilisers should I apply?

In our previous article, “Do your crops lack potash?”, (ProAgri Zambia No 46, page 14) we discussed the critical importance of balanced fertilisation in crop production.

In this article, we focus on vegetables, as these are particularly vulnerable to farming techniques and the environment. To achieve high output, growers should apply correct fertilisation, plant spacing, weeding, molding, pollination and pruning.

Thorough management becomes especially important under suboptimal weather conditions. Excess rainfall can lead to significant yield losses due to ponding, nutrient leaching and the spreading of diseases.

For example, correct hilling of potatoes is a good agronomical measure against waterlogging. Another practice that proved to be efficient, is establishing good canopy closure to suppress weeds and decrease their influence on crops.

Fertilisation programmes should also be well established with reference to the type of crop, the growth stage and environmental conditions. A sufficient supply of potassium (K) and calcium (Ca) builds up a strong immune system, sharply reduces the risk of physiological disorders, significantly extends shelf life of fruits, and improves their marketable appearance.

Lack of K is reflected in club-shaped cucumbers and non-uniform appearance of tomato fruits. Ca deficiencies may result in center or stem-end constrictions and fruit curling in cucumbers and blossom-end rot of tomato fruits. There are three primary sources of K in the form of mineral fertilisers: (i) potassium nitrate (NOP), which contains 46,2% K2O and 13,7% nitrogen; (ii) potassium sulphate (SOP) – 50% K2O and 45% sulphur; (iii) potassium chloride (MOP) – 60% K2O.

United Fertilizers Company Ltd (UFCL) also provides compound NPK 10:20:20+6S and NPK 10:26:26+2S as high-concentrated sources of P and K.

The decision which fertiliser to use should be made according to the fertilisation programme based on the chemical analysis of the soil and the needs of specific types of crops. NOP is irreplaceable for crops under glass and soilless growing systems, as it is characterised by a low salt index. MOP is the most concentrated source among K fertilisers, and its use is the most economically efficient due to its low cost. However, MOP should be avoided when soil chloride levels are high.

There are no alternatives for Ca in high output production systems. Calcium nitrate is the only source of fully water soluble and readily available Ca for crops.

UFCL supplies concentrated calcium nitrate, produced by Uralchem under the SOLAR brand. This product does not contain ballast substances (like water or ammonium nitrate) and contains 98% of calcium nitrate against 68% and 78% in tetrahydrate and dihydrate analogues, respectively.

As Ca is hardly redistributable between different plant organs and potassium demand steadily increases along entire vegetation period, your fertilisation planning should include these elements and peak towards fruit formation. For instance, NPK 10:20:20+6S or NPK 10:26:26+2S could be supplied shortly before planting or at the beginning of root formation stage (make sure to put fertiliser to one side of the seedling in order not to burn it). Then, depending on conditions mentioned above, the grower should split applications of nitrogen fertiliser, potassium (NOP, SOP or MOP) and SOLAR calcium nitrate.

More information about field tests will be discussed in follow-up issues and on our website at www.ufertilizers.com.