The road to high yielding and sustainable citrus production

Citrus nutrient requirements

The citrus fruit family comprises of several species, most notably oranges (Citrus Sinensis), lemons (C. limonum), grapefruits (C. paradisi ) and mandarins (C. reticulata), with each type of citrus fruit having several dozen of varieties. Although the nutrient needs of citrus trees are broadly similar, their exact requirements will vary according to the species cultivated and/or plantation growing conditions. In general, high yielding citrus trees will take up large quantities of the major mineral nutrients – nitrogen (N), phosphorus (P), potassium (K), and calcium (Ca).
These macronutrients need to be supplemented by minor quantities of magnesium (Mg), sulphur (S) and micronutrients. Most of the nutrients removed by citrus trees during the growing season are subsequently exported with the fruit at harvest. N, P and K. More precisely, one tonne of harvested oranges removes:

• 1.18-1.90 kg of N
• 0.17-0.27 kg of P
• 1.48-2.61 kg of K
• 0.36-1.04 kg of Ca
• 0.16-0.19 kg of Mg

As with most crops and farming systems, fertilization management is essential to properly regulate the uptake of nutrients by citrus plants and maintain nutrient availability during the growing season in response to demand. A proper fertilization programme is also necessary to maintain soil fertility and citrus productivity over the longer term.

The fertilization programme recommended for citrus varies according to the climatic conditions and production system (irrigated or rainfed). In general, irrigated production systems are found in the Mediterranean climates of both the northern and southern hemispheres – including California, Chile, parts of Australia, South Africa, and the growing areas that fringe the Mediterranean basin in Israel, north Africa, and southern Europe. Rainfed production systems, meanwhile, predominate in tropical and wet subtropical climates that are typical of the main citrus producing regions of China, India, and South America.

For citrus plantations in full production, the fertilization programme needs to consider the nutrients status of soils and crops, the yield target, and the end-market for the produce. Orange and mandarin plantations growing fruit for fresh consumption, for example, need around 200, 100 and 180 kg/ha of N, P₂O₅ and K₂O, respectively, for a yield of 40-50 t/ha, assuming a fertile soil and a well-nourished plantation. These application rates will, however, need to be adjusted according to the nutrient status of the plantation, the end-market and the yield target.

For oranges destined for the juice industry, the fertilization plan requires a higher nitrogen application rate together with a slightly lower application rate for potassium – although, again, these rates need to be adjusted for the yield target and nutrient status of the plantation. In rainfed systems, fertilizers are applied to the soil surface with two-thirds applied under the canopy and one-third outside. The total fertilizer supply is usually split between five or six applications across the growing season. The use of controlled release fertilizers (CRFs), such as ICL’s Agrocote product, is advantageous, as this allows the number of applications to be reduced while, by ensuring a maintained availability ot nutrients, and avoiding “hunger” periods in between fertilizer applications, improving yields as well as nutrient use efficiency (NUE) in most cases. Citrus fertilization programmes can also include ICL’s Polysulphate fertilizer, either applied together in combination with Agrocote or as a separate application. This multi-nutrient (K, Mg, Ca, and S) unique mineral continues to supply nutrients to the plants over extended period due the natural prolonged availability of its nutrients.

In irrigated systems, crop fertilization can combine fertigation with soil on the soil, and with fertigation. ICL’s Agrolution family of water-soluble fertilizers (WSFs) are ideal for the fertigation of citrus trees. Agrolution and Nova product lines provide a complete range of formulations for the requirements of the different stages and different formulations for different kinds of waters, including Nova PeKacid and Agrolution pHLow for fertigation with hard waters. A fertilization programme that combines fertigation (e.g., Agrolution or Nova) with soil application (e.g., Agrocote and Polysulphate) can be suitable for citrus growing in areas with meaningful spring rainfall (>200-300 mm). Fertigation with the Agrolution and Nova product range allows the matching of precise nutrient requirements during most of the season while applying Polysulphate ensures the supply of secondary macronutrients to the crop during wet periods.