Abstract
Biofertilizer enable to improve nutrient cycle in soil and induce plant growth and production, but sweet potatoes farmers in Indonesia are still use only chemical fertilizer as a source of plant nutrient. The objectives of this experiment were to evaluate the effect of different doses of consortium biofertilizer to reduce chemical fertilizer dose; and maintain yield and sweetness of two sweet potato varieties. The experimental design was completely randomized block design which tested six combinations of different chemical fertilizer and biofertilizer doses. Analysis of variance was performed to determine any significant differences between the means of treatments. The results showed that the response of both sweet potatoes varieties on combined application of chemical and bio fertilizer was differ. All treatments did not change tuber number and weight of sweet potato var. Awachy-1 but increased those of var. Rancing. Application of diazotrophic bacteria (Azotobacter, Azospirillum and Acinetobacter) mixed with phosphate solubilizing microbes (Pseudomonas and Penicillium) with reduced fertilizer doses up to 75% did not alter soil available nitrogen and phosphorous. Despite different fertilizer rates, tubers number of both sweet potato varieties in individual plot was similar. Yield did not change due to reduction of fertilizer dose up to 75% when biofertilizer was applied. However, yield was potentially decreased when chemical fertilizer was only 50%. All fertilizer treatments did not change the sweetness of tuber which indicated by constant brix. Research suggested that biofertilizer might substitute 25% of chemical fertilizer to obtain the same yield and quality of tuber, and maintain the availability soil nitrogen and phosphorous.
Highlights
At least 200 varieties of local sweet potatoes grow in Indonesia and mostly exported to other countries and consumed locally as staple food
To overcome limited availability of nitrogen and phsphorous, farmers applied chemical fertilizer combined with organic fertilizer to increase the yield
Nitrogen (N) and Phosphorus (P) are macro essential nutrient for producing marketable tuber (6,14,16). Both nitrogen-fixing bacteria (NFB) and phosphate solubilizing microbes (PSB) are beneficial soil microbes well known as Plant Growth Promoting Rhizobacteria
Summary
At least 200 varieties of local sweet potatoes grow in Indonesia and mostly exported to other countries and consumed locally as staple food. Sweet potato in Indonesia typically cultivated in upland region dominated by low to medium soil fertility includes Ultisols, Oxisols and Inceptisols. These soils order contains low nitrogen and phosphorus that limited plant productivity (9) and become a constrain to increase sweet potatoes productivity. Integrated use of chemical fertilizer and biofertilizer will be important for long term sustainable agriculture in low fertility soil to increase nutrient availability as well as maintain enzymatic nutrient cycle and beneficial microbe occurrence in soil. Nitrogen (N) and Phosphorus (P) are macro essential nutrient for producing marketable tuber (6,14,16) Both NFB and PSB are beneficial soil microbes well known as Plant Growth Promoting Rhizobacteria. Both microbial groups synthesized and secreted phytohormones to the soil; which is in turn uptake by plant roots to regulate cell development and elongation
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