Abstract
Nitrogen management in orchards should tend to improve the fertilizer N use efficiency for a sustainable agriculture where productivity, fruit quality and environment are reconciled. The use of specific nitrification inhibitors could increase the N fertilizer uptake and decrease the potential groundwater pollution by nitrate leaching. The aim of this experiment was to assess the effect of application frequency of the ammonium sulphate (AS) and the nitrification inhibitor (NI), 3,4-dimethylpirazole phosphate (DMPP) supply on: nitrate-N and ammonium-N seasonal changes in soil; N and Fe concentrations in the spring-flush leaves; and yield and fruit quality. The experiment was carried out with clementine cv. Nules (Citrus clementine Hort. Tanaka x Citrus reticulate Blanco) mandarins grafted on Troyer citrange (Citrus sinensis x Poncirus trifoliata) rootstock under field conditions during three consecutive years. The trees were fertilized with 324 Kg N/ha from which 192 Kg N/ha were applied as AS (21% NH4+ -N) either with or without NI, and the remainder N came from irrigation water. The AS and AS+NI were split into 1, 2 or 4 applications per month by drip irrigation. The NH4+ -N concentration in the 0-20 and 20-40 cm soil layers was significantly higher in the AS+NI treatment. By contrast, the NO3- -N concentration was significantly higher in the soil treated only with AS. Moreover, the addition of NI to AS originated a significantly higher N and Fe concentrations in the spring-flush leaves. The yield was higher and some fruit quality parameters improved in trees fertilized with AS+NI compared to those fertilized only with AS.
Highlights
Citrus is an intensively managed crop and the most important economically on the Mediterranean coast of Spain with almost of 3x105 ha, where the cultivation of citrus fruits predominates
The citrus tree root system is comprised of a relative shallow, well-branched framework of woody laterals and fine fibrous roots (Castle, 1980a)
The fibrous roots are usually most densely concentrated near the soil surface while few roots are found below 90 cm (Castle, 1980b; Zhang et al, 1996; Mattos et al, 2003)
Summary
Citrus is an intensively managed crop and the most important economically on the Mediterranean coast of Spain with almost of 3x105 ha, where the cultivation of citrus fruits predominates. Previous studies demonstrated that the nitrification inhibitor (NI) dicyandiamide (DCD) added to ammonium sulphate nitrate (ASN) improved the N-fertilizer efficiency and reduced NO3- leaching in young and mature citrus trees (Serna et al, 1994, 1996a). There is no information about the behavior of the DMPP in Citrus cultivated under field conditions For these reasons, the aim of this research was to evaluate the effect of the DMPP and AS application frequency on the seasonal distribution of NO3- and NH4+ concentration in the upper soil layers, leaf N concentration, yield and fruit quality in a drip-irrigated Citrus orchard
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