The use of ash and biochar derived oil palm bunch and coal fly ash for
improvement of nutrient availability in peat soil of Central Kalimantan

anion  bonds  to  store  nutrients  longer,  and  reduces levels  of phenolic  acid  compounds  (Hartatik  et al., 2003).   Generally,   biomass   such  as  compost   and manure   are   applied   as   ameliorants   in   peat  soil (Widyati et al., 2010; Maftu’ah and Indrayati, 2013; Damanik  and Anwar, 2016).  However,  this practice could increase the amounts of carbon emissions into the atmosphere  due to  the  decomposition  of organic matter (Widowati et al., 2011). Therefore, wise efforts to  reduce  the  increasing  carbon  emissions  due  to organic matter decomposition  and the maintaining of soil fertility are greatly needed.

The potential ameliorant which can improve peat soil fertility can be obtained from oil palm plantation and electric steam power station (PLTU). Productive waste from the manufacture of crude palm oil (CPO) can be used in the form of  oil palm empty bunches biochar  (OPFEB)  and oil  palm  boiler  ash (POBA). One of the productive wastes in the PLTU is coal fly  ash (CFA). Indonesia has 14.3 million hectares of oil palm plantation areas with CPO production at a rate of 29.3 million tons in 2018. In the same year, Central Kalimantan  has  1.51  million  ha  with  a  total  CPO production  of 6.04  million  tons  (Central Bureau  of Statistics, 2019). OPFEB contribute 23% of biomass from CPO production (Indriyati, 2008). Therefore, the potential biomass obtained reached 1.39 million tons from    6.04    million    tons    of    CPO    processed. Management  of  OPFEB  is  still  limited.  Generally, some of them are just stacked around  the road, and others are composted. OPFEB biomass modified into biochar has been investigated by Ichriani et al. (2018). In addition,  the oil palm boiler ash (POBA) derived from  the  shell,  and  palm  fibre  combustion  at 800- 900oC is generated by CPO production. The POBA has alkaline pH and contains 30-40% K2O, 7% P2O5, 9% CaO and 3% MgO (Ricki et al., 2014).

The  coal  combustion  process  in  power  plants station produces 5% solid pollutants in the form of ash. The resulting ash consists of 80-90% CFA, and the rest is coal bottom-ash.  The  estimated coal demand  for domestic  power  plant  station  fuel  needs  by  2027 reaches 162 million tons (PT. PLN, 2018). Coal fly ash contains a high amount of Fe, Ca, Al, Si, K and Mg, a moderate amount of Zn, B, Mn and Cu, and a  small amount  of  C and  N  percentage.  The  chemical  and biological toxicity analysis showed that CFA contains less leached heavy metal, it is almost non-toxic, and it is   relatively    harmless    (Dzantor   et    al.,    2015; Damayanti, 2018). Therefore, CFA can be utilized for improving rice productivity (Prasetyo et al., 2010) and maize     productivity   (Kaur    and    Goyal,    2015; Fahrunsyah et al., 2018).

The objective of this research was to study the ability   of  OPFEB   biochar,   POBA,   and   CFA   in enhancing  the  nutrient  availability  in  peat  soil  of Central Kalimantan.

Materials and Methods

Peat  soil  used  was  collected  from   Kalampangan, Sebangau,   Central  Kalimantan   (2o16’57.9”   S  and 114o01’27.0” E). Oil palm fruit empty bunch (OPFEB) was kindly donated by PT Surya Inti Sawit Kahuripan, Parenggean,       Kotawaringin       Timur,       Central Kalimantan. The production of biochar from OPFEB was   conducted   in   the   Laboratory   of   Bioenergi, Universitas   Tribuwana   Tunggadewi,   Malang.   The biochar construction was done as a slow pyrolisis at Kalimantan. The chemical properties of CFA were the pH H2O = 9.8, total P =1378.56 ppm, total N= 0.05%, and total K =719.35 ppm (Fahrunsyah  et  al., 2018). The giant Salvinia aquatic plant (Salvinia molesta) was used as compost raw materials. The production of S. molesta compost was carried out in the greenhouse of the Department of Agronomy, Faculty of Agriculture, Palangka Raya University. The chemical properties of the compost were pH H2O (1:5) = 4.87, total P = 0.1%, total N = 0.6%, MgO = 0.19%, CaO = 0.77%, and K2O = 0.31%. The peat soil was air-dried for 7 days and sieved using a 2 mm mesh sieve, and weighed by 500 g/polybag.   The   preliminary   results   of   chemical properties of peat were pH H2O (1:5) = 3.06, available P  (Bray  I)  =  82.11  ppm,  exchangeable  K  =  0.61 cmol/kg,   exchangeable   Mg  =  1.32  cmol/kg,   and exchangeable  Ca  =  4.34  cmol/kg.  Each  ameliorant material  was  applied  on  peat  at  a  rate  of  15  t/ha (biochar,  POBA,  and  CFA)  and  20  t  compost/ha. Seven  treatments,  namely OPFEB biochar,  oil palm boiler  ash  (POBA),  coal  fly  ash  (CFA),  compost, OPFEB  biochar  + compost,  POBA  +  compost,  and CFA  +  compost,  were  arranged   in  a  completely randomized    design   of   single    factor   with   four replications.  The ameliorant sources were applied on peat soil and incubated for four weeks. The humidity was  maintained   at  field  capacity.  At  the  end  of incubation,  soil  samples  were  taken  for  laboratory analysis of pH H2O 1:5 (electrode glass), exchangeable K, Ca, and Mg (atomic absorption spectroscopy), and available  P (Bray I) (Soil Research  Institute,  2005). Statistical  analysis of observed data was done  using Analysis  of  variance  with  F-test  at  5%   level  of significance  followed  by  Duncan’s  Multiple  Range Test (DMRT) at p = 0.05.

Results and Discussion

Soil pH

Biochar,  POBA, CFA and compost gave  significant enhancement of peat soil pH compared to its initial pH (Figure 1). The low increment at a  rate of 0.1 point occurred  on CFA  treatment  which was higher  than POBA, CFA and compost application. The result is in line with Maftu’ah and Indrayati (2013) investigation on coconut shell biochar in peat soil. Application  of biochar + compost that increased the pH by 0.72 points showed   that   the   combination   of   compost   with inorganic ameliorant (biochar and CFA) increased soil pH. The effective improvement of pH that was resulted from  the soil buffering  reaction  was caused  by the combination  of  organic  and  inorganic  ameliorant, particularly     biochar.     The    decomposition     and mineralization of compost produce CO2 functioning as a buffer compound  to increase soil pH (Bohn et al., 1985; Stevenson, 1994). In addition, the compost and biochar   contain   the   negatively   functional   groups (Ichriani et al., 2018) that are beneficial to bind soil H+ (Bohn et al., 1985). Peat soil has organic compounds that come from the result of decomposition of organic matter  and  high  in  lignin  content.   Lignin   which undergoes   a  degradation   process  under   anaerobic condition, will break down into humic compounds and phenolic acids. Phenolic acid is one of the contributors to acidity in peat soils due to the functional groups (i.e. carboxyl   groups,   hydroxyl   groups).   Lesbani   and Badaruddin (2012) reported that humic acid extracted from Muara Kuang Ogan Ilir peat soil was dominated by  carboxyl  groups  (-COOH)  of 560  mmol/kg  and hydroxyl groups (-OH) of 125 mmol/kg. 

The activity of organic acids (especially phenolic acid derivatives)  can be reduced through the provision of biochar, POBA, and CFA. Increasing the resistance of rice against organic acid poisoning resulted from the application  of  EPOEB  ash  was  able  to  reduce  the concentration of phenolic acid derivatives, i.e. ferulic, syringic,   and   p-cumarate   (Haryoko,   2012).   The decreasing  of  hydroxybenzoic  acid  and  p-coumaric from 53.45 ppm and 26.18 ppm to 0.24 ppm and 0.13 ppm  were  demonstrated  by  ameliorating  peat  soil using fly-ash from pulp boiler waste (Rini et al., 2007). The addition CFA of 5% by and 15 t/ha by increased soil pH on peat soil. In our study, the increase in soil pH was low, indicating the organic acid activity decrease was not maximal.

The availability of K, Ca, and Mg

The peat soil nutrient status underwent changes with the application of biochar, POBA, CFA and compost (Figure   2).  A  significant   increment   occurred   on exchangeable   K  and  exchangeable   Ca  except  for exchangeable    Mg.    However,    these    ameliorants showed inconsistent positive effects in the availability of peat soil nutrients such as compost, which impacted the increase  of  availability  of K, Ca, and Mg.  The   nutrients impacted by POBA that was higher than CFA treatment  has  not  been  able  to  improve  the  soil nutrients   in  the  short   term   (Utami,   2018).   This phenomenon was due to the impact of CFA and POBA as slow-release ameliorant resulting in a long time to dissolve and increase the nutrient content in the soil. The CFA and POBA ameliorant sources contain high macro  and  micronutrients  (Sulistiyanto  et al., 2015; Fahrunsyah et al., 2019).

However,   the  compounds   contained   in  CFA   and POBA were crystalline silicate compounds that were formed  due  to  heating  to  high  temperatures.   The crystalline  silicate compounds resulted in macro and micronutrients  difficult  to  dissolve. Likewise,  OPEFB biochar  has a structure  of aromatic  ring  compounds  (C  =  C)  and  crystalline which is formed from cellulose and lignin compounds.  These structures are formed due to the high heating of cellulose and lignin compounds in the slow pyrolysis process.

The GCMS analysis of OPEFB biochar indicated that    the    dominant    organic    compounds  presumably  in the form of cyclopropane compounds (15.51%)  and cycloheptatriene compounds  (12.04%). The  application  of biochar or biochar+compost  could escalate the availability of K nutrient, among others. In the short term, biochar was able to increase the availability of K, and in the long term,   it   had   the   effect   of   preserving   nutrients. Biochar application has increased 69-89% availability of soil K and the residual biochar still has a positive.

 

Presumably  in the form of cyclopropane compounds (15.51%)  and cycloheptatriene compounds  (12.04%) . The  application  of biochar or biochar+compost  could escalate the availability of K nutrient, among others. In the short term, biochar was able to increase the availability of K, and in the long term,   it   had   the   effect   of   preserving   nutrients. Biochar application has increased 69-89% availability of soil K and the residual biochar still has a positive.

effect  on  the availability  on the soil K in the  next growing  season.  Synergism between the mixing of inorganic ameliorants (biochar, POBA, and CFA) and organic ameliorants (compost) triggered    an    increase    in   exchangeable    K   and exchangeable Ca because of its capability to provide higher K and Ca availability compared to the unmixed treatments.

The  increase  in soil  nutrients  availability  was thought  to  be  due  to  the  presence  of  organic  acid compounds  such  as  humic  acid  compounds  from compost. Besides, the process of decomposition  and minerals release through compost mineralization      results      in      increased      nutrient availability.

Availability of P

The application of biochar, POBA, and CFA provided a significant increase in the peat soil P availability (Figure 3). The biochar + compost amendment produced the lowest P compared to other treatments, even though there was an increase of 135.7% available P compared to the initial P of the soil. Application of coconut shell biochar mixed with chicken manure was able to increase the available P of peat soil from 31.63 ppm P2O5 to 232.03 ppm P2O5. Other studies have shown similar results that the CFA application can increase the availability of nutrients in the soil, including the et al., 2016). This is because soil P is dominated by organic P. Soil P is also bound by organic acid compounds . The total orgnic P of peat soils from Air Sugihan Kiri, South Sumatra, ranged from 77-90% and P-inorganic 10-23% P nutrient . The significant enhancement in P availability was not optimal when compared with the total P content in the ameliorant source because all P compounds were not changed completely into available form. The total P content at POBA was 6,492.44 ppm P2O5 and 1,378 ppm P2O5 at CFA. In peat soil, the availability of inorganic P is low.
The not optimal availability of P is thought to be due to not all P compounds  contained  in the  ameliorant material have changed into available forms. Another thing is thought to be due to the low activity of soil microbes  that  help  dissolve   phosphate,   especially phosphate solubilizing microbes. Soil microbes helped dissolve phosphate, especially phosphate solubilizing microbes,    through   their   organic    acid   secretion (Cunningham and Kuiack, 1992). The soil pH of peat soil  was  low  (Figure  1), indicating  a high  level  of acidity.  Soil  acidity  conditions  do  not  support  the presence  of  microbes,  so  that  the  activity  of  the phosphate    solubilizing    microbial    is    still    low. Phosphate solubilizing microbes are able to secrete the enzyme   phosphatase   and   low   molecular   weight organic  acids,  namely  oxalate,  malic,  succinic,  and fumarate. The existence  of the enzyme helped the hydrolysis of P soil which were still bound to form soluble P or available P (Lal, 2002). Soil cations (Al3+, Fe3+, and Ca2+) which fixation of P can also be chelated  by  organic acids derived  from phosphate  solubilizing  microbes  ().  This  mechanism  has  the effect of increasing soil P availability and efficiency of P fertilization. The production of phytohormones,   vitamins,  or  amino  acids  resulted from  the  activity  of  soil  microorganisms  may  also affect  soil  P release. Therefore,  further  research on the application  of the indigenous   phosphate   solubilizing   microbes   and specific locations needs to be studied to maximize the availability of P in agriculture on peat soils.