Development of a user friendly and cost effective nutrient management strategy for simplified hydroponics

Abstract

To increase the profitability in agriculture, low cost, readily available, simple, attractive technologies which can utilize space and water efficiently are required. Simplified hydroponicsis a system that is affordable and also adaptable to any part of Sri Lanka. So far,no scientific research involving simplified hydroponics technique has been reported in Sri Lanka. For this technique to be used locally, it is important to develop a formulationfor a nutrient solution which is of low cost, suitable to the climatic conditions in SriLanka and compatible with locally available, low cost growing media such as rice hulland river sand. The possibility of introducing a buffer system and use of silicon as a beneficialelement were considered when designing the new formulations. In this study, two new formulations "new formulation with silicon" (NFS) and "new formulationwithout silicon" (NF) were prepared using locally available commercial gradechemicals. A buffer system KOH / KH2P04 (with a capacity of 4 mmol / dm\ was incorporatedinto the new formulations. Potassium silicate with a molar ratio of Si : K of I: 0.53 (prepared using sodium silicate and KOH) was selected as the source of silicon in thenewformulation, NFS. The composition of formulation, NF was (in ppm), N = 167, P = 80,K = 281, Ca = 234, Mg = 57, S = 251, Cu = 0.01, Fe = 3.9, Zn = 0.13, Mn = 1.2 and Mo= 0.13. The composition of formulation, NFS was the same as that ofNF, except for S (Ill ppm) and Si (l00 ppm). In both formulations, the ratio ofN: K was 1: 1.7. The"inertness"of the medium (rice hull: sand = 3 : 2) was evaluated by determining the cationexchangecapacity(CEC),anionexchangecapacity(AEC)andby leachingstudies withdistilledwater and Albert's solution. Both CEC (7.38 Cmmol/ 100 g) and AEC (14.17x3 Cmmol/ 100 g) were low. Only very small quantities of nutrients (except Si) areleachedfromthe medium. Unlike with sand, leaching of silicon ions from rice hull increasedwith time. Since rice hull was used as a medium in this study, it was not possibleto studythe effect of silicon on plant growth. "Albert's solution" (CIC) is the commercially available nutrient pack widely used by farmersand for research in Sri Lanka. The drawbacks of this nutrient pack were studied andsolutionswere sought. On analyzing the "Albert's solution", the compositions of the workingsolutions prepared were found to vary greatly especially with respect to the micronutrients. The most suitable weights of "Albert's solution" for plants were 1.6 g (pH 6.12 and EC 1.63) and 2.6 g (pH 6.01 and EC 2.92) in 1.0 dm3 of tap water. The weightof undissolvedmatter of both the solutionsincreasedwhen the pH was increased from5.8 to 6.5. At pH above 6.1 in the working solution of "Albert's solution", it is likelythatFe,Ca and pol precipitate while at pH 6.5, sol precipitates as CaSO4.Mn ' alsoprecipitatesin sampleshavinghigheramountsof Mn at this pH. Whenthe pH is increasedfrom6.1 to 6.5, the amount of Ca in the precipitate increases by 3 - 4 fold whiletheamountof Fe in the precipitate increases by two fold.