Productivity gains in vegetables from rice husk biochar application in nutrient-poor soils in Timor-Leste

Abstract

Response to fertilisation with biochar is greatest in field crops on acidic tropical soils, but limited information is available for vegetable crops. As a case-study using vegetable production in Timor-Leste, we assessed if biochar alleviates nutritional constraints to vegetables in low-nutrient soils. Field trials on vegetable crops were conducted with fertiliser combinations of rice husk biochar, phosphate and local fertiliser at three sites. A pot soil incubation trial of biochar was undertaken with soil from the acid site, where rice husk biochar had a larger effect on productivity than the other fertilisers in chili pepper, tomato and soybean with an average yield increase with biochar of 230% over control. Combining phosphate with biochar augmented the yield over biochar alone in chili pepper, tomato and soybean. At neutral and alkaline sites, fertilisation with biochar lifted mean yield over the control. Soil constraints alleviated by fertiliser were primarily from P and Zn deficiencies. Marked increases in vegetable yields, among the highest globally, were achieved with fertilisation with biochar individually and in combination with phosphate in low nutrient soil in Timor-Leste. Clearly, rice husk biochar is a promising avenue to fertilise the soil with P and Zn and increase crop productivity in Timor-Leste.

Figure 1

Mean yield (t ha⁻¹) over crops of response to fertiliser treatments (1. Control (no fertiliser application); 2. Local fertiliser regime (see details below); 3. Fertilisation with rice husk biochar (20 t ha⁻¹ at Triloka and 30 t ha⁻¹ at Caibada and Natarbora); 4. Addition of SP36 (28.8 kg P ha⁻¹ and 4 kg S ha⁻¹); and 5. The combination of biochar (Treatment 3) and SP36 (Treatment 4) at (A) Caibada, (B) Natarbora and (C) Triloka study locations. The local fertiliser treatment varied by site according to local usage: At Caibada 10 t cow manure ha⁻¹ applied; at Natarbora 100 kg NPK (15:15:15) with 2 t cow manure ha⁻¹; and at Triloka 1.2 t cow manure ha⁻¹. Standard errors are indicated as error bars.

Figure 2

Response in soil pH to different biochar application rates (0, 5, 10 and 20 t ha⁻¹) for 26 weeks after application in the soil incubation trial. Interaction LSD (P < 0.05) = 0.18.

Figure 3

Changes in available P, K and Zn in an acid soil incubated for 26 weeks with four rates of biochar application (0, 5, 10 and 20 t ha⁻¹). Data shown are as a percentage of the critical concentrations of 18, 100 and 3.8 mg kg⁻¹ for Mehlich 3 extractable P, K and Zn, respectively, based on Wortmann et al. (2019).