Fertigation frequency, wetting patterns and nitrate leaching from lysimeter-grown citrus trees

J.P. Syvertsen, S.M. Sax

Abstract


Eighteen 'Hamlin' orange (Citrus sinensis [L.] Osb.) trees on 'Swingle' citrumelo (C. paradisi Macf. × Poncirus trifoliata [L.] Raf.) rootstock were individually transplanted from the nursery into 7.6 m3 (2000 gallon) lysimeter tanks filled with native Candler sand, irrigated similarly and grown for 5 years from 1994 to 1998. During 1997-98, all tanks were fertigated at similar annual rates of N using 360°; or 180°; pattern microsprinklers. To investigate management practices that might minimize leaching of NO3-N, six trees with 360°; jets and six trees with 180°; jets were fertigated weekly (avoiding rainy periods) or 28 times in each year. Six additional trees with 180°; jets were fertigated twice as often using only half the amount of N in each application. There were no effects of wetting pattern or irrigation frequency on canopy growth, tree water usage, fruit yield or quality in either year. Root density and total root wt. in the 180°;-wetted zone was greater than that in the non-wetted root zone but wetting pattern (180°; vs. 360°;) had little effect on the total N leached in Iysimeters. Thus, results of this study do not support the idea of reducing NO3 leaching by reducing the wetted surface area of the soil. The 180°; treatment with 56 split applications per year, leached the least N, 38% and 40% of that applied in 1997 and 1998, compared to about 53% and 52% in the other treatments. These results underscore the importance of a high frequency of split applications in reducing the concentration of N that is susceptible to leaching. Using frequent fertigations, well-fertilized young citrus trees can be grown on a vulnerable soil and still maintain NO3-N concentrations in ground water that do not exceed the maximum contamination level, 10 mg N liter1.


Keywords


'hamlin' orange; 'swingle' citrumelo; nitrogen; tree growth; evapotranspiration; fruit yield; fruit quality

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Proc. Fla. State Hort. Soc.     ISSN 0886-7283