Transcript PowerPoint-Präsentation - International Plant Nutrition Institute

Universität
TROZ Centre for Agriculture
Hohenheim
in the Tropics and Subtropics
Institute of Plant Nutrition (330)
A BIOLOGICAL DISEASE-MANAGEMENT SYSTEM FOR
CITRUS PRODUCTION IN SAO PAULO STATE / BRAZIL
1. PROBLEM
2. OBSERVATIONS
During the last decade, severe distribution of the bacteriosis CVC
(Citrus Variegated Chlorosis, Xylella fastidiosa; Fig. 1B) and of the
virus "Sudden Death" (Tristessa Virus) has been observed in widespread traditional citrus production systems. Intensive use of herbicides (Glyphosate) and of mineral fertilizers, applied between the
tree rows is characteristic for these production systems (Fig.1A).
Meanwhile, more than 50% of the citrus orchards in Sao Paulo State
are affected by these diseases and farmers have to change to other
crops (e.g. sugar cane).
In some organic farms, a biological management system with
intensive mulching using Brachiaria grass (Fig. 2A) and without
application of herbicides, alleviated or even avoided expression
of disease symptoms on trees and fruits (Fig. 2B).
Traditional Biological
A
B
Mn 12.3
Zn 13.3
A
49.0 mg/kg
57.3 DM
Brachiaria mulch
B
Fig. 2A/B) Biological production system
Fig. 1A/B) Traditional production system
3. WORKING HYPOTHESIS
Predominant use of nitrate fertilizers in the traditional Citrus production
system limits plant availability of Mn and Zn (Fig. 1B), which is further
aggravated by regular application of Glyphosate herbicides (Tab.1). A low
Mn-, and Zn-nutritional status will result in low disease resistance (e.g.
against CVC).
In contrast, in the innovative biological production system, Brachiaria
mulch inhibits nitrification, which will lead to rhizosphere acidification by
preferential ammonium uptake and will thereby increase the plantavailability of Mn and Zn, which is further improved by omission of
Glyphosate herbicides and inoculation with Mn-mobilizing microorganisms
(e.g. Trichoderma as biofertilizers; Fig.3)
Fig. 3) Model for the working hypothesis
4. RESEARCH APPROACH
4.1 Field Experiments in Brazil
In Sao Paulo State, three field experiments (Novais, Ibira, Uchoa) with
varied fertilization (Fig.4) were set up as a long-term study.
4.2 Model pot experiments in Hohenheim
with Citrus seedlings, sunflower and soybean as model plants.
- Incubation experiments to confirm inhibition of nitrification
under Brachiaria mulch and resulting rhizosphere acidification.
- Nutrient solution-, and rhizobox-experiments to demonstrate
inhibition of Mn acquisition by root-released glyphosate from
target plants (Table1, Fig.5) and improved Mn uptake by inoculation with Mn-mobilising microorganisms (Trichoderma).
Conventional practice (Glyphosate)
Conventional + soil and foliar Mn, Zn
Conventional + (NH4)2SO4+ NI
Conventional + (NH4)2SO4+ NI + Mn, Zn
Conventional – Glyphosate
Conventional + Trichoderma konegeir.
Innovative with Brachiaria mulch
Innovative + soil and foliar Mn, Zn
Treat Mn-Translocation (rel. values)
Innovative + (NH4)2SO4+ NI
ment Sunflower Soybean Soybean
Innovative + Trichoderma konegeir.
BTX
(NI = Nitrification inhibitor)
Fig. 4) Field experiments in Brazil
5. EXPECTATIONS
An improved Mn(Zn)-nutritional status will result in:
- better disease resistance against CVC and Sudden Death
- reduced application of herbicides
- improved soil fertility and reduced soil degradation by mulching
as an approach for sustainable citrus production
Glyphosate
0%
100
2%
4
6%
3
100
12
4
100
57
60
Table 1) Effect of glyphosate at drift concentrations (2% and 6% of the recommended
minimum Dosage = 15%) on Mn translocation
in sunflower and soybean plants at 24 h after
glyphosate application.
Soybean
Target
Sunflower
Indicator
Fig. 5) Chlorosis symptoms on sunflower leaves after simultaneous
cultivation with Glyphosate-treated
soybean plants
M. Guldner, G. Neumann, V.Römheld - Institute of Plant Nutrition (330), Hohenheim University, Stuttgart, Germany
R. Cabrera - Novais-SP, Brazil
co. V. Römheld: Phone: +49 711 459 3714
T. Yamada - POTAFOS – Piracicaba-SP, Brazil
Fax:
+49 711 459 3295
I. Cakmak – Sabanci University, Istanbul, Turkey
e-mail: roemheld@uni-hohenheim.