Soursop Grower's Tips

1.Will higher productivity of soursop during current season require more fertilizer for next season?

  • When the plants are producing fruit, the amount of fertilizers required should also be based on the nutrients removed in the harvested fruits. In fact the nutrients removed in the fruit are an excellent guide to establish a fertilization programme for any fruit tree such as soursop. The quantity of each nutrient removed by the fruit on average of each 1mt of harvested soursop fruits are as following:
    • 2.0 to 2.7kg Nitrogen
    • 0.4 to 0.5kg Phosphorus (0.9 to 1.1kg P2O5)
    • 2.0 to 3.5kg Potassium (2.4 to 4.2kg K2O)
    • 0.2 to 0.9kg Calcium (0.3-1.3kg CaO)
    • 0.1 to 0.2kg Magnesium (0.2-0.3kg MgO)
  • Balance fertilization is important to make sure soursop plant receive sufficient nutrients within the optimum level. N and K are the nutrients in greatest demand by soursop, the amounts should increase proportionally with the age of the plant and its level of production. However, care should be taken avoid excess N because this causes the plants to grow too quickly and produce less fruit.
  • Solution:
    • Adequate fertilization for different growing stage is a basic condition for getting excellent result.
      • At planting: good seedling growth will result in a productive adult plant producing good quality fruit. The fertilizer NIFOSK GREEN 17-17-17 shall be applied which provide sufficient nutrition for the plant setting up.
      • During growth: After planting the seedlings, the fertilizer NIFOSK GREEN 17-17-17 and NIFOSK S BLUE 12-12-17+2MgO+8S+B+ZN+TE should be applied during the next three years (based on the actual growth on site). Fertilizer should be applied around the plant but only lightly incorporated into the soil to avoid damaging the developing root system whilst putting the fertilizer near them. In a dry area, the fertilization with higher P fertilizer should be used at the beginning of the rainy season.
      • During production: Fertilizer with high K such as NIFOSK S 15-5-20+2MgO+25S+TE is in greatest demand by soursop during production stage, the amounts should increase proportionally with the age and size of the plant and its level of production. On sandy soils and others where there is a risk of N and K being lost by leaching, N and K fertilizers should be applied more frequent during the growing season.

2.Are trace elements (TE) important to soursop plants?

  • In general, soursop is sensitive to trace elements, especially Zn, B and Iron deficiency.
  • Zinc (Zn): Within the plant, Zn functions as an activator of enzymes and is involved in the producing the growth hormones. A zinc deficiency can result in poor plant growth and development. The Initial symptoms include interveinal chlorosis on young leaves, which can be similar to those of iron deficiency. In later stages of zinc deficiency, newly emerged leaves will likely to be narrow and remain small. Symptoms that might occur as the severity level increases are shortening of the internodes, necrotic spots, and bronzing of the leaves.

  • Boron (B): Like Ca, B is immobile in phloem and for this reason the first symptoms of its deficiency occur in the young leaves. During flowering and the fruiting stage, maintaining adequate amounts of plant-available B and Ca reduces the possibility of internal darkening of the pulp, which is common in soursop.
  • Iron (Fe): Like Ca and B, the redistribution of Fe in the plant is practically zero. Thus the initial symptoms of Fe deficiency occur in the young leaves and are characterized by partial chlorosis with yellowish-green coloration of the lamina, which with time becomes totally yellow except in the region around the veins.
  • Solution:
    • ; an EDTA micronutrient water soluble fertilizer designed for irrigation and foliar application.
    • Not all trace elements are available to the plant. A high pH level could result in the trace elements precipitating. The same applies when the pH level is low. When this happens, the micro element is no longer available to the plant.
    • In order to prevent precipitation of trace elements, chelates EDTA has been used in TRACEION 5Fe/2.5Zn/2.5Mn/0.5Cu/1B/3Mgo/0.05Mo.
    • What are chelates? Chelates are organic molecules that have the possibility to keep many elements available in the fertilizer solution. Thanks to this claw named the chelate, the transport of nutrients towards the roots is ensured.

3.How to prevent Anthracnose to reduce damage during post harvest?

  • Disease management is one of the major tasks in soursop planting. Controlling these are essential for quality fruits and higher crop yields.
  • The common disease found in soursop are mainly root rot and anthracnose. Anthracnose is a fungal disease caused by Colletotrichum species that is detrimental to numerous fruit, including soursop.
  • The rapid softening during postharvest storage is one of the most critical problems that avoid the commercialization of this fruit. Moreover, other factors have also reduced fruit quality such as irregular production, and pathogen attack. In this regard, fruits are attacked by the fungi Colletotrichum spp., which produce a disease called anthracnose.
  • Solution:
    • Other than the use of fungicides, one alternative to this problem is the biological control using FOSFIKA, which has been applied successfully against this pathogen. The plants have generated defence mechanisms that allow them to tolerate the damages caused by pathogens.
    • FOSFIKA is able to activate the pathogen-induced signals that trigger defence strategies specific to plant immunity. One of these mechanisms is the induction of systemic defence such as phytoalexins and pathogen-related (PR) proteins to block the pathogen directly. These molecules send systemic alarm signals to the non-infected neighbouring cells and induce defensive response mechanisms including cell well modification via deposition of polysaccharides.

4. How to increase soursop fruit weight and size?

  • It is essential to improve the size and quality of fruits. Various study proved about positive effect of Potassium Nitrate on fruit yield and quality of plum.
  • Potassium nitrate (KNO₃) is a soluble source of two major essential plant nutrients. It’s commonly used as a fertilizer for high-value crops that benefit from nitrate (NO₃-) nutrition and a source of potassium (K+) free of chloride (Cl⁻).
  • Growers value fertilizing with KNO₃ especially in conditions where a highly soluble, chloride-free nutrient source is needed. Potassium nitrate contains a relatively high proportion of K, with an N to K ratio of approximately one to three.
  • Solution:
  • Applications of KM SANGRALINE PN 13-0-46+IODINE can be done during fruiting stage. A diluted solution also can be used as foliar application on plant foliage to stimulate physiological processes or to overcome nutrient deficiencies.
    • Foliar application of K during fruit development advantages soursop plants, since this growth stage often coincides with high K demands during the time of declining root activity and nutrient uptake.