+14% export yield in Capsicum Pepper thanks to improved root development with Ultrasol®ine K Plus

The application of Ultrasol®ine K Plus resulted in improved root growth, reduced incidence of BER and 14% higher yields of exported fruit in Capsicum bell pepper.

Iodine (I) should be considered as a plant nutrient. This is the main conclusion of Kiferle et al., 2021. In that work they published the presence and identity of natural iodinated proteins in higher plants, which had never been described before. Eighty-two iodinated proteins have been identified that are involved in important biological processes in higher plants. Like deficiency of any other plant nutrient, iodine deficiency can lead to yield losses.

In fertigation and protected horticultural crops grown in a commercial production environment, iodine deficiency can occur when the presence of iodine in the nutrient solution is below a target value of sufficiency. In intensive and fertigation under cover cropping systems, the nutrient solution and irrigation water are the main sources of iodine. This deficiency will manifest itself in the form of suboptimal root or leaf development, delayed flowering, reduced fruit growth and reduced stress resistance, resulting in lower yields compared to a crop that has been supplied with sufficient iodine in the nutrient solution.

To demonstrate the effect of improving iodine supply in an iodine-deficient crop, Ultrasol®ine K Plus (potassium nitrate containing a fixed amount of iodine) was applied as a source of K and N - and iodine - in the nutrient solution of an Italian type sweet bell pepper 'Kapiamo' in sandy soil at a commercial production site in Agadir, Morocco. The effect of this application was compared with that of the normal iodine-deficient nutrient solution in two plots of 1 ha each in adjacent greenhouses. Prior to the trial, irrigation water samples were taken and the iodine concentration in these samples was measured. The iodine concentration in the irrigation water was less than 0.1 μmol ^L-1, which was considered deficient.

Both greenhouses were planted with the same variety, on the same date, and fertigated with the same nutrient program. The only difference between the greenhouses was the use of the regular potassium nitrate source in one greenhouse, and Ultrasol®ine K Plus in the other. Ultrasol®ine K Plus was applied starting in November, two months after transplanting in late August, and continued until the end of harvest in May. Table 1 shows the composition of the concentrated solution, injected 2 times per week into the irrigation system. A total of 420 kg _KNO3/ha was applied in each greenhouse between November and May. The total yield for the season was recorded for both greenhouses separately.

The farmer observed clear differences in crop development between the sectors. The first notable difference was root growth. In the control greenhouse, root growth was as expected from the grower's experience. In the greenhouse where Ultrasol®ine K Plus was applied, a clear improvement in fresh root growth was observed throughout the greenhouse (Figure 1). At the end of the season, total fruit yield was 10% higher in the greenhouse where Ultrasol®ine K Plus was applied, and in particular the yield of export quality fruit was 14% higher in that greenhouse compared to the greenhouse with a low iodine supply (Table 2). The higher yield of export quality fruit was related to a lower incidence of fruit quality disorders such as apical rot (BER, Figure 1). Clearly, here the application of iodine prevented the

yield loss due to lower fruit quality as a result of iodine deficiency.

Apical rot is a fruit quality disorder that is related to a local calcium deficiency in the distal part of the fruit. The cause of this calcium deficiency is a complex interaction between the ability of the root system to absorb calcium from the root solution, the rate of expansion of the developing fruit, and the ability of the vascular system to transport calcium to the apical end of the fruit to meet the calcium demand in that tissue. Iodine enhances root growth and acts synergistically with potassium nitrate to improve calcium uptake from the root zone and calcium translocation to the fruit. In addition, the effect of iodine to enhance photosynthesis and prevent leaf and root stress may explain the grower's observations of improved root system and reduced incidence of root-end rot (ER) in the crop that has been supplied with sufficient iodine in the root zone with Ultrasol®ine K Plus.

Table 1. Fertilizer sources, injected twice a week into the irrigation system, from 200 L of a concentrated stock solution.

Figure 1. Improved root growth and reduced incidence of apical rot of bell pepper fruits in the greenhouse where Ultrasol®ine K Plus was applied.

Table 2. Improved all-season Capsicum bell pepper fruit yield in the greenhouse where Ultrasol®ine K Plus was applied.

La publicación original está disponible en: https://doi.org/10.17660/ActaHortic.2021.1321.27