LIBRO-CONGRESO-CITRUS

gas exchange, foliar SPAD index and yield when compared with superficial irrigation. On the other hand, deficit
irrigation increased P, K and Na foliar concentrations but reduced yield and affected fruit quality (increasing
fruit acidity). Overall the results indicate that deficit irrigation and the sub-surface irrigation system can be
both used as measures for increasing plant WUE. However, PRD, contrarily to previous evidence obtained
in more arid environmental conditions, did not allow any gain in plant performance when compared with a
similar watering regime. Our results question the applicability of the more expensive PRD irrigation system in
the commercial citrus orchards of the Valencia region.
S10O06
A critical evaluation of citrus leaf mineral status guidelines for optimal yield in Israel
Raveh E.
Agricultural Research Organization (ARO), Fruit trees, Israel. eran@agri.gov.il
Maintaining orchards at optimal leaf mineral concentration is one of the key issues for maximal yield. Experiments
for verifying and updating guidelines are very rare since they require several years of field experiments in mature
bearing trees which are expensive. The evaluations of such guidelines at the grower level are more complicated
processes and therefore usually not done. -In the present paper we first evaluate the Israeli guidelines for citrus
by comparing them to the Israeli orchards leaf mineral status using a 10 year leaf mineral database (results from
20244 leaf analysis that were sampled from commercial orchards all over Israel). Then we tried to create an
updated guideline using a second database that summarized yield and leaf mineral concentration collected from
122 orchards all over Israel over 7 years (the Israeli National Wastewater Effluent Irrigation Surveys database).
There was a disagreement between the local recommendations and the orchards leaf mineral status (e.g local
recommendation were higher than orchard median values), which demonstrates the needs for guidelines
updating. Based on the Israeli National Wastewater Effluent Irrigation Surveys database a new guideline was
set. It was found that the optimal leaf mineral concentration for grapefruit is 1.7-2.1% DW of N, 0.08-0.010% DW
of P, 0.37-0.48% DW of K, and 0.33-0.45% DW of Mg. For orange trees the optimal leaf mineral concentration is
1.9-2.3% DW of N, 0.11-0.14% DW of P, 0.80-1.00% DW of K, and 0.19-0.26% DW of Mg. For easy peelers trees
the optimal leaf mineral concentration is 2.0-2.4% DW of N, 0.09-0.12% DW of P, 0.55-0.69% DW of K, and 0.19-
0.26% DW of Mg. Maintaining the leaf within this rages can allow maximal yield of 110-120 t/ha for grapefruits,
65-70 t/ha for oranges, and 60-70 t/ha for easy peelers.
S10O07
What limits nitrogen fertilization responses of fertigated citrus orchards under tropical
conditions?
Mattos Jr. D. 1 , Quaggio J.A. 2 , Boaretto R.M. 1 , Souza T.R. 2 , and Zambrosi F.C.B. 2
1 Instituto Agronômico (IAC), Centro de Citricultura Sylvio Moreira, Brazil; and 2 Instituto Agronômico (IAC), Centro de Solos e Recursos
Ambientais, Brazil. ddm@centrodecitricultura.br
Fertigation of citrus orchards was recently adopted by growers in Brazil. The inherent low fertility and
acid soils under the tropics implies that efficient nutrient management practices need to be conducted to
ensure high fruit quality and yield. A field experiment with Valencia sweet oranges on Swingle citrumelo was
established in 2003 when trees were 3-4-year old and conducted during a six-year period. Trees received
60, 120, 180 and 240 kg/ha per year of N, as ammonium nitrate (AN) or calciun nitrate (CaN), via fertigation
using two dripper lines per row. Fruit yield for pooled data reached 70 t/ha with 180 kg/ha of N as AN, what
agrees with reported fertilization curves, in which this maximum is attained with N rates of approximately
200 kg/ha. On the other hand, fruit yield increased linearly up to 85 t/ha with the highest N rate as CaN. Soil
analysis demonstrated that acidification was greater after AN applications. In this case, soil pH was below
4.6 in the surface and 3.8 at deeper soil layers despite frequent liming applications to the soil. This resulted
from increased ammonium uptake by roots, what correlated with nutrient concentrations in soil solution
extracts. Leaf Ca was