Effect bulking agent on composting mexican sunflower (Tithonia diversifolia L) biomass and utilization on pak choi production

Jahra Pelu, Setyono Y. Tyasmoro, Moch. Dawam Maghfoer Department of Plant Science, Faculty of Agriculture, University of Brawijaya, Malang, East Java, Indonesia. Department of Agrotechnology, Faculty of Agriculture, University of Brawijaya, Malang, East Java, Indonesia. Department of Agrotechnology, Faculty of Agriculture and Forestry, University of Iqra Buru, Namlea, Maluku, Indonesia. Email: yayan2406uniqbu@gmail.com


INTRODUCTION
Food safety issues and environmental concerns about effect of the intensive use agrochemical in green revolusi era has contribute to development of organic farming over the last years. Compost almost use as a soil fertilizer or soil conditioner and to substitute commercial fertilizers in crop production. It has organic matter and nutrients content are valuable materials for increasing chemical, physical, biological properties of soil, stimulating root respira-tion and improve plant growth and yield (Cayuela et al., 2009;Guo et al., 2012). Compost is a product of breakdown biodegradable organic materials by microrganism into stabilized materials under controlled condition (de Bertoldi et al., 1983;Hubbe et al., 2010).
This biomaas potentially used as the main ingredient for composting. However, it has C/N ratio <15 where it were lower than those recomended for composting process (Bernai et al., 1998;Cayuela et al., 2009;Sahwan, 2004;Sweeten & Auvermann, 2008) caused fast mineralization nutrient especially in intial composting process that potential losses (Mahimairaja et al., 1994). Beside it, high moisture content of these biomass filled air pores and inhibit oxygen circulation or anaerobic condition. This condition can disrupt activity of microorganisms for decomposition process. Excessive moisture content of compost pile are leached also carry out dissolved nutrients that substansialy reduces the nutrient value of the compost product (Adhikari et al., 2009;Maurya et al., 2018;Sundberg, 2005;Tiquia & Tam, 2000).
Previous study showed that cocomposting high C/N and low moisture bulking material (bulking agent) with low C/N ratio and high moisture organic materials were an option strategy to provide optimizing condition for microbial activities on decomposition organic materials (Bernal et al., 2009;Nugroho et al., 2010). Bulking materials modify and prevent physical compaction of substrates, balance C/N ratio of compost pile, increasing aeration rate and improving biological activity conditions and regulation of moisture (Adhikari et al., 2009;Epstein, 2011;Rosiana et al., 2013;Zaman & Sutrisno, 2007).
Low moisture content of bulking agent can absorb leachate during decomposition and keep the moisture in the pile to sustain the composting process (Adhikari et al., 2009;Iqbal et al., 2012), reduce nutient losses and thus improving nutrient content of final Products (Gabhane et al., 2012). However, difference of C/N ratio, carbon structure, physical shape, particle size of bulking agent affected water absorption capacity, rate of decomposition, nutrition conserve and quality of final compost (Barrington et al., 2003;Bustamante et al., 2008;Chang & Chen, 2010;Supadma & Arthagama, 2008).
There were about 20-30% rice husk as waste from rice mill. It has been used as soil amendment or additive/bulking agent in composting (Adhikari et al., 2009;dela Cruz et al., 2006;Dewi et al., 2013;Zaman & Sutrisno, 2007). Convert rice husk by biochar technology to produce a char materials with higher carbon and more pore than raw rice husk (Theeba et al., 2012) that will optimizing composting process and quality of compost. However, information about effect of raw rice husk (RRH) and rice husk char (RHC) on composting T. diversifolia L biomass and compare it's potential as soil amandment and fertilizer were scarce. Therefore, we are take more attention about it in this work.
Pak choi (Brassica rapa var chinensis) is a leafy vegetable with high nutrient content, antoxidant, anticarcinogenic, antiviral properties to maintain human health. The content of vitamins A, C, folic acid, beta-carotene and calcium in pak choi is higher than other types of cabbage (Opena & Tay, 1994;Tshikalange, 2006). Pak choi often widely planted in a pot / container system because it has a shallow root structure (Boonsiri et al., 2009). The result of this study hopefully will provide practical information to use T. diversifolia L biomass compost with different bulking agent as a novel soil amandments and fertilizer on organic agriculture system.

MATERIALS AND METHODS
Research to evaluate quality of compost Compost processed in open windrow The change of temperature correlate with microbial activities during composting process (Kumar et al., 2010;Wahyono et al., 2008).
Therefore, dynamic temperature of compost pile were used as parameter to monitor the performance composting process in this study.
Gambar 1. The temperature dynamics on composting processes of T. diversifolia L biomass with bulking agent raw rice husk (RRH) and rice husk biochar (RHC). Dynamic of temperature (Figure 1) showed that there were different trend of temperature dynamic although the initial C/N ratio of TRRH and TRHC compost piles were appropriate recommended range for optimum decomposition (Bernal et al., 2009) post. Difference microbial actitivity due to different initial C/N ratio initial compost mixture (Theeba et al., 2012;Zhu, 2007). Use RHC as bulking agent on T. diversifolia L provide balance carbon an nitrogen to support growth of microorganisms and promoted abundance microbial communities. Therefore, THRC has high microbial activity than TRRH. Contrasted with previous works by (Zhu, 2007)  Losses of P and through run-off and leaching (Tiquia et al., 2002). Total phosphor (TP) decreased by 18.97% (TRRH) and 9.64% (TRHC) respectively ( Figure ). Phosphor losses in TRHC < TRRRH compost because high carbon content of RHC than RRH affected C/P ratio of composting mixture and mineralization rate of phosphor organic on beginning composting process (Dias et al., 2010). Therefore, if the concentration is low, the potential for losses by leaching were low too. Biochar has internal porosity, high surface area and surfaces sites promote absorption of nutrient and have high cation exchange capacity to retain cation include HPO 4 + (Laird et al., 2010;Novak et al., 2009). Therefore, it is assumed that this mech-anism also caused low losses of P on TRHC compost than TRRH compost.
Biochar increase soil chemical properties such as cation exchange capacity, (Biederman & Harpole, 2013;Gusmailina, 2010;Masulili et al., 2010;Prendergast-Miller et al., 2014;Spokas & Reicosky, 2009) (Gusmailina, 2010;Lehmann & Rondon, 2006) and boosts plant growth (Schulz et al., 2013) Release of nutrients from TRHC. 40 provide enough nutrients for pak choi and supported by the presence of biochar in THRC which has range of pore sizes. Micropores serve as capillary spaces with high surface area to volume ratios and can retain water dan nutrient. while macropores of biochar can serve as gas exchange channels which can directly influence root respiration . Asai et al. (2009) and Yu et al. (2013) stated that biochar has potential to increase water holding capacity and increase crop yields in loamy sand soil. Schulz et al. (2013) Prost et al. (2013) found that increased water holding capacity also help retained dissolved nutrient prevent nutrient losses, increase water available for plants and decreased drought stress of plants (Liu et al., 2012;Sohi et al., 2010). The porous structure of biochar were a suitable habitat for microbial proliferation