Papaya is one of the most important tropical produced fruits. Production and consumption has increased due to its popularity as source of nutrients for human diet. Papaya has a high potassium (K) requirement due to its yield potential and constant bearing. Research shows important improvements in fruit quality and yield under adequate soil and plant K levels.
Papaya (Carica papaya) production ranks among the top ten fruit crops produced worldwide with about 12.4 t produced during 2012 (FAOSTAT, 2014). More than the half of papaya production takes place in Asia, where most of the fresh fruit is destined for exports. From the nutrition standpoint, papaya is an important source of vitamins A and C, iron, as well as papain, which helps to improve digestion in humans. Ideal fruit size varies depending on the destination market but the dominant types are small (0.45 to 0.70 kg) and large (up to 4.5 kg) papayas. The major limitations for papaya production are diseases, such as ringspot virus and post-harvest pathogens, which could result in up to 60% yield loss. Additionally, there is a need to improve nutrition practices, particularly in developing countries, where fertilizer production practices are a limitation for papaya production.
Uptake of K in papaya is relatively high compared to other crops due to its high yield potential, early bearing, and continuous growth. Thus, it is important to maintain a constant K supply, especially after pollination to ensure adequate fruit size and quality traits, such as sugar, papain, and latex content, as well as pulp thickness, and carotenoid levels. Nitrogen (N) and K are usually applied at 1:1 ratio (Jeyakumar et al., 2008; Kumar et al., 2006; Oliveira and Caldas, 2004), with split applications throughout the season to avoid K deficiencies, which could affect crop growth and yields.
Deficiencies of K include interveinal and edge chlorosis in old leaves first, followed by necrosis of leaf edges, and ultimately leading to leaf drop. Under severe deficiency, plant stunting is also observed. On the other hand, excess of K application will lead to a reduction of calcium, magnesium, and boron plant uptake. Available research on the effects of K fertilizer management on papaya quality and yield has improved both situations. However, more efficient and sustainable practices are needed around the world to increase yields.
Figure 1. Potassium deficiencies in papaya. Left side: K-deficient plant. Right side: adequate K supply (credits: IPI, 2016).
Case Studies. A study was conducted by Kumar et al., (2006) to identify the effect of K rates on papaya growth and yield. Treatments consisted of following K rates: 0, 150, 300, and 450 g/plant/year of K2O equivalent. Fruit weight was significantly affected by K fertilizer rates with the highest weight observed at 300 g/plant/year with a detrimental effect at further K fertilizer increments (Figure 2).
Figure 2. Effect of K application rates on fruit weight and fruit total yield in papaya production (from Kumar et al., 2006).
Another study was conducted to determine the effects of K and N fertilization in papaya quality. Treatments consisted in the combination of four doses of K (380, 475, 570, and 665 g of K2O) and N (320, 400, 480, and 560 g/plant). Leaf tissue analysis were collected at early blooming and differences in papaya quality parameters were analyzed. Results showed a significant positive correlation between leaf K content and pH pulp and soluble solid content (SSC) in papaya fruits. Fruit pulp pH was around 5.0 in all treatments (Figure 3A), which is within the accepted ranges for the papaya processing market. With regards to SSC content, the highest value was measured at 37.5 g/kg K leaf content (Figure 3B).
Proper K fertilizer management has the potential to improve other papaya quality traits such as pulp thickness and acidity, which in combination would result in better fruit quality for the fresh and processing market.
Figure 3. Effect of K leaf tissue concentration on pulp pH (A) and fruit soluble solid content (B) in papaya production (from Santos et al., 2015).
Food and Agriculture Organization of the United Nations, Statistics Division. (2015). FAOSTAT. Available at: http://faostat3.fao.org.
International Potash Institute. (2016). K gallery. Available at: http://www.ipipotash.org/en/kgallery#ipi-slide65.
Jeyakumar, P., Amutha, R., Balamohan, T. N., Auxcilia, J., and Nalina, L. (2008). Fertigation improves fruit yield and quality of papaya. In: II International Symposium on Papaya, 851, 369-376.
Kumar, N., Meenakshi, N., Suresh, J. and Nosov, V. (2006). Effect of potassium nutrition on growth, yield and quality of papaya (Carica papaya L.). Indian Journal of Fertilizers, 2(4), 43-47.
Oliveira, A. M. G., and Caldas, R. C. (2004). Papaya yield under fertilization with nitrogen, phosphorus and potassium. Revista Brasileira de Fruticultura, 26(1), 160-163.
Santos, E. M., Cavalcante, I. H. L., da Silva Junior, G. B., and Albano, F. G. (2015). Impact of nitrogen and potassium nutrition on papaya (pawpaw) fruit quality. Bioscience Journal, 31(5).