Early winter spray of low biuret urea improves marketable yield and fruit quality of sweet oranges

The purpose of this study was to determine the optimum time of low-biuret urea (LBU) applied as a foliar spray to improve marketable yield and fruit quality of Sweet Orange (Citrus sinensis L. Osbeck.) cv "Blood Red́. Two percent solution of LBU was sprayed on 15 years old plants to the point of run off, on 15 ^th of October, November and December in 2004. Simple water spray was used as control. Plants selected for the experiment were grafted on rough lemon (Citrus jambhiri Lush.) rootstock and were grown at University of Agriculture Faisalabad (Latitude 31° 25' North; Longitude: 73° 09'), Pakistan. Experiment was laid out in RCBD, using single plant as a treatment unit with three replicates. Foliar spray of 2% LBU on 15 ^th November, 2004 significantly increased total yield (102%) as well as grade-I fruit yield (75%) compared with control. Fruit quality including pulp colour score (40%), TSS (33%), vitamin C (10%), TSS/TA (19%), sugars (44%) and taste score (37%), of November treated samples were significantly greater as compared to control. Significant decrease in fruit weight, fruit diameter, and number of aborted seeds/fruit was recorded in all the treatments as compared to the highest values in control, followed by the treatments applied on 15 ^th of December, October and November, 2004 respectively. Highest value of 108.3g for fruit weight and 56.9mm diameter were found in plants treated on 15 ^th November, 2004. No effect was observed in juice contents, peel weight or acidity with LBU treatments. Overall, foliar spray of 2% LBU applied on 15 ^th November, 2004, produced better results for improving marketable yield and fruit quality of "Blood Red́ sweet orange.