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Growth and flowering of young cocoa plants is promoted by organic and nitrate-based fertiliser amendments
- Smilja Lambert, Hussin bin Purung, Syawaluddin, Peter McMahon
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- Journal:
- Experimental Agriculture / Volume 56 / Issue 6 / December 2020
- Published online by Cambridge University Press:
- 15 December 2020, pp. 794-814
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Cocoa (Theobroma cacao) farmers in Sulawesi, Indonesia typically use subsidised, ammonium-based rice fertilisers that in combination with poor agricultural practices have resulted in soil acidification, loss of organic matter, aluminium toxicity and lower soil fertility. As a result, these soils are only marginally appropriate for replanting cocoa to boost production. A field experiment was performed to test alternative soil amendments for successful replanting of cocoa on these deficient soils. In a trial with a randomised block design, 6-month old seedlings, top-grafted with the local MCC02 clone, were planted under light Gliricidia sepium shade and after 3 months treated quarterly with two options of mineral fertilisers: either a customised fertiliser, consisting of Nitrabor (a combination of calcium nitrate and boron), dolomite, rock phosphate and KCl or a NPK/urea mix used by farmers, each supplied with or without ‘micronutrient’ rock salt, organic fertiliser and beneficial microorganisms or their culture medium, a mixture of chitin and amino acids (a total of 20 treatments). Over a 4-year period, the marginal mean rates of stem diameter increment and flowering score were higher in customised fertiliser than NPK/urea treatments. The average growth rate was highest in the first year and was increased by supplying organic fertiliser. A significant correlation (r = 0.22, p < 0.05) occurred between growth and available P, but concentrations of available P were higher in the NPK/urea plots, which also had lower mean growth rates. Combined supply of organic fertiliser and microbes increased available P, as well as growth rates, in both the customised and NPK/urea treatments. In contrast, NPK/urea-treated plots without these amendments demonstrated very low growth rates. The customised formulation was more effective with or without added organic fertiliser or inoculated microbes. Micronutrient supply stimulated flowering. Growth rates in trees supplied with NPK/urea were also promoted by micronutrients. Leaf flush production occurred in regular cycles and was unaffected by the nutrient amendments. After 3 years, the customised and organic fertiliser application increased soil pH and exchangeable Ca and Mg concentrations, although they remained below recommended levels for cocoa production. These treatments had little impact on soil C content (about 1.3%) which was also deficient. Exchangeable Al and total Zn concentrations were higher in soils amended with NPK/urea. The results of the trial provide evidence that utilisation of organic fertiliser in combination with customised nitrate-based formulations improves cocoa establishment, growth and soil properties and should be recommended as a replacement for the NPK/urea fertilisers traditionally used by farmers.
EFFECT OF ORGANIC AND INORGANIC AMENDMENTS ON PRODUCTIVITY OF COCOA ON A MARGINAL SOIL IN SULAWESI, INDONESIA
- SAHARDI MULIA, PETER J. MCMAHON, AGUS PURWANTARA, HUSSIN BIN PURUNG, FADJRY DJUFRY, SMILJA LAMBERT, PHILIP J. KEANE, DAVID I. GUEST
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- Journal:
- Experimental Agriculture / Volume 55 / Issue 1 / February 2019
- Published online by Cambridge University Press:
- 10 November 2017, pp. 1-20
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Reduced soil fertility and damage from pests and diseases have contributed to a decline in productivity of cocoa (Theobroma cacao L.) smallholdings in Sulawesi, Indonesia over the last decade. In a trial on a marginal, acidic soil in South Sulawesi, young PBC123 cocoa trees were supplied with compost, mineral fertiliser (NPK fertiliser and urea) or dolomite, alone and in combination. After 20 months, the trees supplied with compost were taller, flowered more profusely and had a five-fold higher dry bean yield than other treatments. Treatments had no impact on incidence of cocoa pod borer, Phytophthora pod rot and vascular streak dieback. All of the trees supplied with compost survived, while the control, mineral-fertiliser- and dolomite-treated trees had a mortality rate of 22–45% and symptoms of interveinal necrosis. Leaf concentrations of N, P and K were within the normal range in all treatments. In the control and mineral fertiliser treatments, leaf concentrations of Ca (0.28–0.30%) and Mg (0.11–0.15%) were deficient, but were higher in trees supplied with compost (0.78–1.21% and 0.26–0.29%, respectively). The Mg/K ratio in soil-exchangeable cations and leaves was increased three-fold by the combined compost/dolomite treatment. Supplying mineral fertiliser alone resulted in 3.3 cmol kg−1 exchangeable Al, compared to 2.2 cmol kg−1 in control soils. Since 10 kg tree−1 year−1 compost was supplied, a rate that is not practical on most cocoa smallholder farms, further investigation of cost-effective applications of organic matter in conjunction with appropriate formulations of inorganic fertilisers is recommended.
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