Nitrogen in Sap of Citrus Trees Under Fertigation.

The citrus industry is a segment of great importance to Brazil, which is the world largest producer of orange. Fertigation is a technique that is increasingly expanding in the citriculture, but this technique is usually performed using predetermined doses without monitoring the nutritional status of plant and soil. The mismanagement of fertigation can cause imbalances in the conditions of soil and plant nutritional status over time. Traditional techniques for monitoring the condition of the soil and the plant do not allow the provision of data quickly, wasting this great potential of fertigation. This research project was aimed at evaluating the effect of five Nitrogen rates on the sap, observing the sensitivity of this method. For this, an experimental work was conducted in the city of Reginópolis-SP/Brasil, using ‘Hamlin’ trees, grafted on citrumelo Swingle rootstock. The treatments consisted of five N rates, applied through fertigation: T1 - control (no nutrient), T2 - 25%, T3 - 50%, T4 - T5 and 100% - 200% of N and K. The 100% rate, officially recommended, was established based on historical of soil and leaf analysis and also in accordance with the expected productivity. The remaining rates was calculated from it. To monitor the nitrogen status on the plants, sap analyses were performed. The nutrients dynamics in the soil was evaluated by soil sampling and by the soil solution analysis, with the help of porous covering soil solution extractors. The N concentrations in the sap correlated significantly with the N rates applied and with the N in the soil and soil solution, what means that sap analysis can be an efficient technique to recommend the Nitrogen fertilization.