The Modelling Study for Potassium Fertilizer Requirements in Hazelnut (Corylus avellana L.)
Potassium is probably the second most important nutrient in hazelnuts (Corylus avellana L.) and an adequate supply of potassium is required for the maximum yield and nuts with high quality. The available amount of this element is often insufficient in soils and must be supplied as fertilizers, which is an essential input for the successful nut agriculture. This modelling study was conducted to determine potassium fertilizer requirement depending on the existing potassium levels of hazelnut orchard soils in the Black Sea Region. The trial was carried out on 'Tombul' (Turkish hazelnut variety) hazelnut orchard in Hazelnut Research Station located in the Black Sea Region, Turkey. It was designed as a randomized complete block design with five potassium doses (0, 200, 400, 600 and 800 kg ha-1 K2O) and three replications per treatment. Besides, other nutrient elements were applied according to the soil analysis results. During three years, each hazelnut ocak (hazelnut branch planting system) was harvested and their total yield was determined. In order to determine the impact value of existing potassium in soils and fertilizers, Modified Mitcherlich equation log (A-y) = log A-c1.b1 was used. Using Mitcherlich equation, the impact value of the existing potassium in the trial orchard soils was found as c1=0.0026, the impact value of potassium in the fertilizer was found as c=0.0038. Potassium fertilizer amounts which should be used according to the contents of various potassium nutrient elements in the soils were calculated by using the log (A-y) = logA-c1b1-cx equation. The obtained data were analyzed with regression and to achieve the maximum yield values at different rates, the formula Y=a+byxX can be used on the calculation of the amount of fertilizer. In order to obtain 90%, 92%, 94%, 96%, 98% and 99% yield out of the maximum product level in hazelnuts, useable models on the potassium fertilizer recommendations were determined as Y90=263.0-0.684X, Y92=289.0-0.684X, Y94=322.0-0.684X, Y96=368.0-0.684X, Y98=447.0-0.684X and Y99=526.0-0.684X.
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