PENGARUH ASAM HUMAT TERHADAP PERTUMBUHAN BIBIT KAKAO (THEOBROMA CACAO) DAN POPULASI MIKROORGANISME DI DALAM TANAH HUMIC DYSTRUDEPT - Santi, Laksmita Prima (Balai Besar Penelitian dan Pengembangan Sumberdaya Lahan Pertanian, 2016)
Abstrak: Asam humat merupakan bahan organik alam yang ketersediaannya cukup melimpah dan berpotensi dalam meningkatkan pertumbuhan tanaman. Peran asam humat dalam meningkatkan kadar hara bagi bibit kakao dan perkembangbiakan bakteri serta sifat kimia Humic Dystrudept tekstur berpasir menjadi fokus utama dalam riset ini. Kegiatan riset ini dilaksanakan di Pusat Penelitian Bioteknologi dan Bioindustri Indonesia pada tahun 2014. Populasi Azotobacter beijerinckii dan Aspergillus niger di dalam tanah dievaluasi di laboratorium. Perlakuan dengan penambahan 0; 2,5; 5,0; 7,5; 10,0; and 12,5 mL asam humat ke dalam 10 kg tanah steril. Sementara itu pengujian di rumah kaca untuk mengetahui pengaruh asam humat terhadap pertumbuhan bibit kakao didesain dengan Rancangan Acak Lengkap dengan dua belas perlakuan dan tiga ulangan melalui penambahan 25; 50; 75; 100 % dosis pupuk NPK; 3,75; 7,5; 11,25; dan 15 mL asam humat; 100% NPK + 7,5 mL asam humat; 50% NPK + 7,5 mL asam humat; 25% NPK + 7,5 mL asam humat ke dalam 10 kg tanah; dan blanko (tanpa pupuk dan asam humat). Berdasarkan penelitian ini diketahui bahwa penambahan asam humat memiliki korelasi positif terhadap peningkatan populasi mikroorganisme tanah dan serapan hara. Kelimpahan terbesar dari populasi A. beijerinckii dan A. niger diperoleh pada penambahan 7,5-12,5 mL asam humat. Penambahan asam humat serta kombinasinya dengan pupuk NPK dapat meningkatkan kadar hara daun N (5,7%), P (21,4%), dan K (17,2%) serta 5,4 - 41,7% bobot kering bibit kakao. Abstract. Humic acid is a natural organic material relatively abundant and potentially be used to improve plant growth. The role of humic acid in improving nutrient content of cocoa seedlings and in improving the growth of soil bacteria and fungi, as well as improving chemical properties of sandy Humic Dystrudept were the main foci of this research. This research was carried out at Indonesian Research Institute for Biotechnology and Bioindustry in 2014. Population of Azotobacter beijerinckii and Aspergillus niger in the soil were evaluated in the laboratory. Treatments were the addition of 0; 2.5; 5.0; 7.5; 10.0; and 12.5 mL humic acid into 10 kg of sterile soil. The greenhouse experiment to determine the effects of humic acid on the growth of cocoa (Theobroma cacao) seedlings was arranged in a completely randomized design with three replications and twelve treatments: 25; 50; 75; 100 % dosages of NPK fertilizer; 3.75; 7.5; 11.25; and 15 mL humic acid; 100% NPK + 7.5 mL humic acid; 50% NPK + 7.5 mL humic acid; 25% NPK + 7.5 mL humic acid into 10 kg of soil; and blank (without fertilizer and humic acid). The results of these research showed that humic acid have a positive correlation in increasing soil microbial population and nutrient uptake. The most abundant population of A. beijerinckii and A. niger were under the addition of the 7.5-12.5 mL of humic acid. The addition of humic acid and its combination with NPK fertilizer increased N content 5.7%, P content 21.4%, and K contents 17.2% in cocoa seedling leaves and seedling dry weight 5.4 - 41.7%.