LIBRO-CONGRESO-CITRUS

S10
optimum value. Available nitrogen content was highest in XH and the lowest in JS, but all of the areas were
lower than the optimum. There was similar trend for leaf nitrogen content. Phosphorus contents in soil and
leaves varied in different areas; tree leaf phosphorus from XH and BJ reached the optimum value, while others
were lower than that. Soil potassium was the lowest in JS and LX orchards, while leaf potassium content in all
area orchards was lower than the optimum value. Magnesium and calcium availability in soil were high in all
areas, but very low in leaves. Zinc in all areas reached the optimum value in both soil and leaves. Data of fruit
quality analysis indicated that Ponkan fruits from five areas had similar fruit weight, TSS and titratable acid,
while fruits from XH presented the highest sugar and lowest acid contents.
S10P18
Boron supply affects growth of citrus and correlates with hydraulic conductivity and gas
exchange of rootstock varieties
Mesquita G.L., Mattos Jr. D., Ribeiro R.V., Boaretto R.M., and Quaggio J.A.
Instituto Agronômico (IAC), Tecnologia de Produção, Brasil. gelm_1@hotmail.com
Boron (B) nutrient disorders cause malfunction of the vascular cambium and growth inhibition. The
nutrient distribution and its concentration in the leaves of citrus vary among rootstocks, mainly due to the
characteristics of roots and water transport in the plant. The objective of this study was to evaluate the
effect of B availability on tree growth, and correlate it to hydraulic conductivity and gas exchange of two
citrus rootstock varieties. The experiment was conducted in nutrient solution in a factorial design with 1-yrold
Valencia orange trees on two rootstocks: Swingle citrumelo (SW) and Sunki mandarin (SK) supplied with
three B levels: poor, adequate and excessive (0, 0.5 e 2.5 mg L -1 of B). The hydraulic conductivity of the plant
(KL) and gas exchange were measured 130 days after beginning the experiment, when plants were collected
and separated into roots, stems and leaves for dry mass estimations. The dry mass production, KL and CO 2
assimilation (A) were differentially affected by the levels of B. Growth and KL increased linearly with B rates
in the nutrient solution for trees on SW [81.3 g per plant and 3.16 mmol(H2O) m –2 s –1 MPa –1 , respectively],
whereas A was maximum with the adequate nutrient level (3.49 µmol m -2 s -1 ). Excess B caused significant
injuries on trees on SK, which showed optimum plant growth, KL and A with the adequate B level [53.3 g per
plant; 6.02 mmol(H 2 O) m –2 s –1 MPa –1 , and 6.05 µmol.m -2 .s -1 , respectively].
S10P19
Silicon uptake in citrus and the validation of an analytical method
Vahrmeijer J.T. 1 , Asanzi N.M. 2 , and Taylor N.J. 2
1Citrus Research Inernational (CRI), Fruit Production and Quality, South Africa; and 2University of Pretoria (UP), Plant Production and
Soil Science, South Africa. jtv@up.ac.za
The importance of silicon as a beneficial element for improving yield and quality of many crops, including citrus,
is well-known. However, whilst analytical methods to determine Si in plant material have been developed and
the uptake of Si in other plants is well documented, there is limited information on the uptake and analysis
of Si in citrus. Therefore, experiments were conducted to validate an analytical method for Si and to assess
the uptake of Si in citrus. Microwave-assisted digestion was used for Si extraction and the Si concentration
was determined with an induced couple plasma optical emission spectrum (ICP-OES), which was compared
to the standard colorimetric method. Silicon uptake experiments in citrus varieties (Valencia and Clementine)
were conducted in winter and summer with two Si formulations, potassium silicate and silicic acid and was
applied to the roots (0, 75 and 150 mg kg -1 ) and as a foliar spray (0, 100 and 500 mg L -1 ). A correlation of 98%
was found between the ICP-OES and the standard colorimetric method.- The uptake study results showed no
significant differences (P≤0.05) in Si content for different Si formulations and citrus varieties, but Si content in
citrus leaves increased significantly (P≤0.01) with maturity. Silicon absorption increased significantly (P≤0.05)
with application rate and Si content in the leaves was significantly higher (P≤0.05) when applied to the roots,
than when applied to the leaves. Si uptake was also significantly higher in summer than in winter.
168 - VALENCIA CONFERENCE CENTER, 18th-23rd NOVEMBER 2012