Biochar, because of its porous nature, calcium carbonate (CaCO₃) equivalent, surface functional groups, and other properties, could serve as an acid soil amendment. To investigate the liming potential of biochars, laboratory characterization and greenhouse and field experiments were conducted in Hawaii and West Java, Indonesia, respectively. Six wood-derived biochars were characterized and amended to a Hawaiian acid soil (pH 4.6, exchangeable aluminum [Al] 1.8 cmolc kg⁻¹) at 2% and 4% alone or in combination with 2 cmolc kg⁻¹ of lime and then planted with Desmodium intortum (a forage legume sensitive to Al) twice in a greenhouse trial. To the Indonesian acid soils (pH 3.9–4.0, exchangeable Al 8–14 cmolc kg⁻¹), a rice husk and a lac tree biochars at 4% and 8% alone or in combination with lime at 4 and 8 cmolc kg⁻¹ and compost at 0.1 and 0.2% were applied and then planted with soybean (Glycine max) cv. Anjasmoro twice in field trials. Biochar effects on soil properties and plant growth were measured. The results indicated that the six biochars varied in pH, ash content, CaCO₃ equivalent, total basic cations, cation exchange capacity, and other properties (pore size, surface functional groups). Soil pH was increased, soil exchangeable Al was reduced, and plant nutrients were enriched to different degrees upon additions of biochars. Total dry weights of Desmodium were increased 2- to 4-fold over the control or lime treatment upon applications of biochar. Similar effects on soils and soybean were obtained for the Indonesian field trials. It was concluded that CaCO₃ equivalent and total basic cations were among the most important properties of biochar responsible for improving acid soil productivity and plant growth.

Highly weathered soils in Hawai’i are low in fertility, negatively affecting plant growth. The potential of biochar for improving soil nutrient availability to crops is promising, and prompts this study. Two biochars at 2% (w/w) made of lac tree (Schleichera oleosa (Lour.) Oken) wood and mixed wood (scrapped wood and tree trimmings) with and without vermicompost or thermocompost at 2% (w/w) were added to an Ultisol (Ustic Kanhaplohumult, Leilehua series) and an Oxisol (Rhodic haplustox, Wahiawa series) of Hawai’i. In each soil two additional treatments—lime + compost and un-amended soil—served as the control. Chinese cabbage (Brassica rapa cv. Bonsai) was used as the test plant in two greenhouse plantings, which had a factorial completely randomized design with three replicates per treatment. The results indicated that soil acidity, nutrient in the soils, plant growth and nutrient uptake were improved by the amendments compared to the control. The combined additions of biochar and compost significantly increased pH and EC; reduced exchangeable Al; reduced Mn and Fe in the Oxisol; increased P, K, and Ca content of the soils; and increased Ca, Mg and Fe uptake. Exchangeable aluminum in the Ultisol decreased from 2.5 cmol+/kg to nil; Mehlich-3 extractable P, K, Ca, Mg, Fe, and Mn in the Ultisol increased by 1478%, 2257%, 1457%, 258%, 125% and 72%, respectively compared to the un-amended soil, while the same nutrients increased or decreased in the Oxisol by 180%, 59%, 308%, −14%, and −36%, respectively. Shoot and total cabbage fresh and dry matters increased by 94%, 96%, 107%, and 112%, respectively, as compared to the lime plus compost treatment. Cabbage growth in the Ultisol amended with the lac tree wood biochar and vermicompost was almost twice over the lime and vermicompost treatment. Essential nutrients in the plant tissues, except for N and K, were sufficient for the cabbage growth, suggesting increases in nutrients and reduced soil acidity by the additions of biochar combined with compost were the probable cause. It is recommended that locally produced biochars and composts be used to improve plant nutrient availability in the highly weathered soils.

Highly weathered soils in the tropics are low in fertility, negatively affecting plant growth. The potential of biochar for improving soil nutrient retention is reportedly promising, triggering this study to assess the nutrient retention capacities of two biochars when applied at 2% in combination with two composts also applied at 2% to an Ultisol (Ustic Kanhaplohumult, Leilehua series) and an Oxisol (Rhodic haplustox, Wahiawa series) of Hawai’i. Chinese cabbage (Brassica rapa cv. Bonsai) was used as the test plant in two greenhouse plantings, which had a factorial completely randomized design with three replicates per treatment. The results indicated that the combined additions of biochar and compost significantly increased the pH, EC, P and K of the soils; improved Ca, Mg and Fe uptake; and increased shoot and total cabbage fresh and dry matter. Exchangeable aluminum in the Ultisol was decreased from 2.5 cmol+/kg to virtually zero. Extractable Mn and Fe in the high Mn-Oxisol were decreased by 55 and 42%, respectively. Chinese cabbage growth in the Ultisol amended with the lac tree (Schleichera oleosa) wood biochar and vermicompost was almost twice over lime at 2 cmol+/kg. Essential nutrients in the plant tissues, with the exception of N and K, were sufficient for the cabbage growth, suggesting increases in nutrients and reduced soil acidity by the additions of biochar combined with compost were the probable cause.

Improving mungbean growth in a semiarid dryland system with agricultural waste biochars and cattle manure

Selada darat (Lactuca sativa L.) merupakan salah satu komoditi sayuran hortikultura yang memiliki prospek dan nilai komersial yang tinggi. Penelitian ini bertujuan menguji efek aplikasi takaran biochar dan kompos kirinyuh tahun keduaterhadap sifat fisik tanah, pertumbuhan dan hasil tanaman selada darat. Penelitian dilaksanakan pada bulan Maret-Mei 2018, dikebun percobaan Fakultas Pertanian Universitas Timor. Rancangan yang digunakan dalam penelitian adalah rancangan acak lengkap faktorial 5 x 3 yang di ulang 3 kali. Faktor pertama adalah takaran biochar yang terdiri dari 5 aras, yaitu 0 t/ha, 2,5 t/ha, 5 t/ha, 7,5 t/ha dan 10 t/ha. Faktor kedua adalah kompos kirinyuh yang terdiri dari 3 aras, yaitut anpa kompos kirinyuh 0t/ha, 5 t/ha, dan 10 t/ha. Campuran tanah, biochar dan kompos kirinyuh yang digunakan tahun sebelumnya, dikeringanginkan, dihaluskan, diayak dan dimasukan kembali ke dalam pot, diairi dan ditanami dengan bibit selada yang telah disemaikan 2 minggu sebelumnya. Parameter yang diamati dalam penelitian ini: suhu tanah, kadar lengas tanah, daya hantar listrik, PH tanah, berat volume tanah, tinggi tanaman, jumlah daun, luas daun, berat segar trubus per tanaman, berat kering per tanaman, Panjang akar, berat segar akar, berat kering akar, rasio akar tajuk, indeks panen. Hasil penelitian menunjukkan bahwa perlakuan biochar pada takaran 2,5 t/ha menghasilkan trubus segar terberat 16,64 g/tanaman lebih tinggi dibandingkan tahun pertama (0 t/ha), sedangkan kompos kirinyuh pada takaran 10 t/ha menghasilkan trubus segar seberat 15.11 g/tanaman lebih tinngi dari pada hasil tahun pertama (0 t/ha). Hasil tersebut menunjukkan adanya aging effect aplikasi biochar sekam padi dan kompos kirinyuh terhadap pertumbuhan dan hasil selada darat.