Improving shallot (Allium cepa Aggregatum group) production in acidic soils in West Java, Indonesia : a dissertation presented in partial fulfilment of the requirements for the degree Doctor of Philosophy of Gina Aliya Sopha in Horticulture at Massey University, Manawatu, New Zealand

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Massey University
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In the West Java region, Indonesia, the wide range of shallot (Allium cepa) bulb yields suggests that there is potential for productivity improvements, especially for smallholder farmers. This study, which involved a farmer and soil fertility survey, two field trials and a laboratory incubation study, aimed to improve the shallot productivity of smallholder farmers. The survey, conducted in four districts of West Java, identified that the Pacet District had the lowest average bulb yield of 5.4 t ha⁻¹ and also had a wide range of yields (2.3 to 11.8 t ha⁻¹). The two common soil fertility constraints were very low soil pH and low available soil phosphorus (P). The first field trial aimed to determine the optimal P fertiliser rates, when rates of up to 1 tonne of lime ha⁻¹ were applied, for three different farm sites in the Pacet District. These sites had strongly acidic soils with constraining exchangeable Al³⁺ and available soil P levels. The second field trial aimed to determine the response of shallot bulb yield to P fertiliser once exchangeable Al³⁺ had been decreased to a low level using high rates of lime. This field trial used a single farm site with a very low soil pHH₂O of 4.1, a high exchangeable Al³⁺ of 1.9 cmol (+) kg⁻¹ and a low Bray1-P of 10 mg P kg⁻¹. The incubation experiment assessed the effect of a range of liming materials, as well as rice husk biochar and zeolite, on soil pH, exchangeable Al³⁺ and cation exchange capacity (CEC). This study quantified the benefits of improved lime and P fertiliser practices and identified constraints to their implementation. Farmers should aim to ensure that soil exchangeable Al³⁺ levels are maintained < 0.5 cmol (+) kg⁻¹, which will be at soil pH levels of approximately > 4.7. Monitoring soil P status through soil testing and achieving Bray1-P levels above 28 kg ha⁻¹ also improves the likelihood of achieving high yields. Very good financial returns can be achieved from high yielding shallot crops; however, farmers need better access to the services of agricultural field officers to conduct and interpret soil tests.
Onions, Yields, Farms, Small, Indonesia, Jawa Barat, soil acidity, lime, P fertiliser, aluminium toxicity