Optimizing the potassium (K) dose of fertigation for the Nagpur mandarin (Citrus reticulate Blanco)

To standardize the potassium sulphate fertilizer dose through fertigation system during three Ambia flowering (October flush) on yield and quality of 14-16 years Nagpur mandarin a field experiment was conducted at National Research Centre for Citrus, Nagpur during 2009-2012. The Nagpur mandarin plants requires potassium besides N and P which, when applied in during the flower bud initiation to before fruit maturity can affect the yield and fruit quality. The treatments in experiment consisted of; F1- Fertigation with 20 g K2O/plant/month, F2- Fertigation with 30 g K2O/plant/month, F3- Fertigation with 40 g K2O/plant/month and F4- Fertigation with 50 g K2O/plant/month. The recommended fertigation dose was 500:150:150 (N:P:K) and given through these treatments along with various fertilizers combination of urea of phosphate, urea and potassium sulphate. Nitrogen and phosphorus was given from October to January month and N, P and K all were given from February to June month. Each fertigation treatment was given at 30 days interval and fruit yield and quality were measured at harvest. Results showed the highest response of the fruit yield (26.67 tonnes/ha) with 50 g K2O/plant potassium sulphate followed by in K-fertigation with 40 g K2O/plant dose (25.52 tonnes/ha). The total soluble solids was highest (9.74 0Brix) in K fertigation with 50 g K2O/plant dose followed by fertigation with potassium sulphate 40 g K2O/plant dose (9.61 0Brix). Highest juice content (39.72 %) and low acidity (0.86 %) was found in K fertigation with potassium sulphate 50 g K2O/plant dose. The highest TSS to acidity ratio (sweetness indicator) was observed in 50 g K2O/plant dose (11.32) followed by 40 g K2O/plant dose Potassium sulphate (10).