Greenhouse experiments were carried out to study the effect of biochar and other organic amendment (Chicken Manure, CM; and City waste compost, CW) using on the growth and N fertilizer requirement of maize. The first experiment was carried out to study the effect of biochar application to maize growth, and then continued to study the residual effect of biochar. The second experiment was carried out to study the effect of biochar application on nitrogen fertilizer requirement. The results show that the first season of maize biomass of organic amendment of treated soils did not significantly different from no organic amendment. However, organic amendment improved soil fertility status, especially increasing C-organic, N, K and CEC. The biomass of the second season maize of biochar of treated soil was higher compared to the other treatments. The second experiment shows that biochar application decreased N fertilizer requirement. To produce 3.23 Mg ha -1 biomass, it required 90 kg ha -1 N for 15 Mg ha -1 CM biochar treated soil, and 160 kg ha -1 for the non treated soil.

: Application of biochar can increase availability of plant nutrients and yield. A field experiment was conducted on anInceptisol with aim to determineresidual potassium fertilizer and biochar application on growth and yield of maize in the second season. A randomized block design was used with three replication. The treaments were residual application of potassium and biochar that consisted of biochar only (30 t/ha), and biochar plus several levels of potassium apllication (0, 50, 100, 150 and 200 kg/ha), included application of 200 kg/ha potassium without biochar. Basal fertilizersapplied in the first season were 90 kg N/ha and 100 kg P 2 0 5 , and in the second season was 90 kg N/ha. The results showed that residual biochar alone or combined with different levels of potassium application increased yield of maize. Residual biochar increased avalilabilty of N, P, K, Ca, and Na in the soil. : biochar, maize, potassium, residual, yield To cite this article: Widowati, Astutik, Sumiati, A. and Fikrinda, W. 2017. Residual effect of potassium fertilizer and biochar on growth and yield of maize in the second season. Keywords

Nutrient leaching is often a problem especially in tropical areas with soil fertility constraints. This study aims to reveal the effect of biochars on leaching and uptake of nitrogen and potassium from degraded soils cultivated with maize. Each of three types of biochar originated from rice husk, wood, and coconut shell, was applied to the soil placed in PVC tube at four rates (0, 15, 30, and 45 t/ha). Maize was then planted in each pot. All pots received urea (135 kg N/ha), SP36 (36 kg P 2 O 5 /ha), and KCl (110 kg K 2 O/ha). Twelve treatments (three biochars and four application rates) were arranged in a factorial randomized block design with three replicates. Results of the study showed interaction effects of biochar materials and biochar rates on nitrate leaching (except on day 1 to 30) and potassium, N uptake, and plant growth. On day 1-30, leaching of nitrate and potassium was reduced by biochar application. The lowest nitrate leaching was observed at rate of 45 t /ha of wood biochar, while application of 45 t coconut shell biochar / ha resulted in the highest K leaching. Beside, wood biochar resulted in a similar nitrate leaching with that of coconut shell biochar, but nitrate leaching increased with increasing rate of rice husk biochar on day 30-60. All biochar materials yielded similar potassium leaching at all rates. Application of 45 t rice husk biochar /ha resulted in the best maize growth.

The increase in black soybean production is constrained by the decreasing productive land area due to increasing population pressure. Dryland is an alternative that can be developed because of its availability. This study aimed to determine the best dosage of biochar and NPK for black soybean plants in dryland. The treatments were arranged in a randomized block design with two factors that were repeated three times. The first factor was the dose of tobacco Jengkok biochar (0, 10, 15, and 20 t ha-1) and the second factor was the dose of NPK Phonska fertilizer (0, 25, 50, and 100 kg ha-1). Soil used for this study was collected from dry land in Gading Kulon Village, Dau District, Malang Regency. Ten kilograms of the collected soil was placed in a polybag and mixed with biochar according to the treatment dose. After 7 days of biochar application, soybean seeds of Detam 1 variety were planted, and soil samples were taken to observe soil organic C, N, P, and K contents. NPK fertilizer was applied according to the treatment dose at 10 days after planting, Plant height and number of leaves were observed at 2, 4, and 6 weeks after planting. Biomass and crop yields were observed at physiological maturity at 85 days after planting. The results showed that the highest levels of organic C, total N, and K were at a dose of 20 t biochar ha-1, but the use of 15 t biochar ha-1 was the optimum dose for biomass and yield of black soybeans. The highest seed weight was obtained from 100 kg NPK ha-1.