Potassium and sodium extraction in cocopeat for potato (solanum tuberosum l.) minituber production under varied calcium nitrate soaking durations and cocopeat-pumice media

Abstract

The low potato productivity of 9-10 tonnes ha-1 in Kenya arose from the rampant use of uncertified seeds in unhealthy soils. The objectives of this study were to improve the cocopeat soilless medium through the extraction of high K and Na using calcium nitrate (Ca(NO3)2) and soaking duration and to evaluate cocopeat-pumice mixtures for potato minituber production. Three successive experiments were conducted in a greenhouse at the Climate and Water Smart Agriculture Centre of Egerton University, Kenya. The treatments for the first and second experiments were five soaking durations (12, 24, 36, 48, and 72 hours) and four levels of Ca(NO3)2 (0, 60, 100, and 150 g) levels mixed with 1.5 kg of cocopeat in 15 litres of water. Soil and untreated cocopeat were used as positive and negative controls, respectively. The third experiment comprised of six cocopeat-pumice mixtures (ratios), viz 100% cocopeat (T1), 75:25% (T2), 50:50% (T3), 25:75% (T4), 100% pumice (T5) and 100% soil (T6). The General Linear Model procedures were used for the Analysis of Variance at (P≤0.05) as well as regression analyses to develop nutrient-to-yield relationships. The result showed that K and Na in treated cocopeat were significantly (P<0.05) reduced by 78.44% and 92.00%, respectively when 1.5 kg of cocopeat was soaked for 36 hours with a concentration of 100 g Ca(NO3)2. In all the treatment combinations, after the cocopeat was washed, the EC was reduced from 1.55 to <1 mS cm-1 and pH from 5.83 to between 5.66-5.71. There were significant (P<0.05) correlation and regression relationships between soaking duration of various Ca(NO3)2 concentrations with K, Na, N, Ca, EC and pH in both the leachate solution and the cocopeat filtrate. For the second experiment, the interaction of Ca(NO3)2 × soaking duration significantly (P<0.001) increased all the yield parameters. The highest growth and yield (464.67 g plant-1) observations were obtained from the combination of 100 g of Ca(NO3)2 with a soaking duration of 36 hours. In the third experiment, the highest (P<0.05) plant heights (67.57 cm and 63.87 cm) and minituber yields (402.68 g and 372.68 g plant-1) were achieved with 100% cocopeat medium followed by the 50:50% cocopeat-pumice mixture, respectively. The highest minituber yields and economic returns were obtained with a 100% cocopeat medium. Seed potato producers using hydroponics systems can effectively optimize concentrations of K, Na; EC and pH levels in (cocopeat soil) media by soaking (ratios) of 1.5 kg untreated cocopeat in 100 g of Ca(NO3)2 for 36 hours.