It is convenient to apply nutrients in fertigation at an appropriate depth, in order to locate those elements at a convenient place for plant uptake. So, an experiment was carried out under laboratory conditions using percolation columns, to establish the irrigation lamina fraction in which N (NH4+ e NO3-), K+, and H2PO4- doses must be applied as well as the optimum dose fractioning of these nutrients so as to locate their adequate depth and determine the distribution of fertigated NH4+, NO3-, K+, and H2PO4-. The treatments consisted of a 4 (1 + 7) factorial, using four Latosols from Minas Gerais (two dystrophic Red-Yellow, one dystroferric Red, and one dystrophic Red), a control (aplication of deionized water) and seven modes of application of 1 mmol dm-3 of NH4+, 1 mmol dm-3 of NO3- , 2 mmol dm-3 of K+ and 2 mmol dm-3 of H2PO4-. The irrigation lamina was divided into five equal fractions (F1 to F5) and the nutrient dose was applied whole (D), or fractioned two (D1/2) or three times (D1/3). Hence, nutrient application was performed according to the following scheme: F2D, F3D, F4D, F2D1/2F3D1/2 , F3D1/2F4D1/2 , F2D1/2F4D1/2 or F2D1/3F3D1/3 F4D1/3. Sub-samples were used to analyze NH4+, NO3-, K+ and H2PO4-, through the determination of the profile of distribution of these nutrients. Mobility was in the following order: NO3- > NH4+ > K+ > H2PO4-, on soils LVAd1, LVAd2 and LVd. For the soil LVdf, the order was: NH4+ > NO3- > K+ > H2PO4- . And the risk of contamination of groundwater caused by NO3-: LVAd1 > LVAd2 > LVdf > LVd. The amount of water added to the column, lower than half pore per volume, was not sufficient to displace H2PO4-beyond the first ring. Regarding the other ions studied, localization at a higher depth when applied as a single pulse, was verified with a higher pulse concentration (D > D1/2 > D1/3) and with a greater irrigation lamina following its application (F2D > F3D > F 4D and F2D1/2F3D1/2 > F3D1/2F4D1/2 ). The results shows that the differential mobility of (N-NNO3- e NH4+ ) and K+ would require a careful dosage of these nutrients in the solution to prevent nitrogen losses due to leaching, or excessively superficial localization of potassium. The extremely low mobility of H2PO4- shows that fertigation would not be an appropriate technique for incorporation of this mineral into soil for crop fertilization purposes.
fertigation; nutrient moviment; nitrogen; irrigation lamina; fratioaneted dose
