Interactions of Biochar Briquette with Ammonium Sulfate Fertilizer for Controlled Nitrogen Loss in Soybean Intercopping with Melaleuca cajuputi

Soybean is a valuable food commodity in Indonesia after rice and maize (Ministry of Agriculture, 2015). The average volume and value of soybean imports over the 6 years (2013-2018) in Indonesia were 1.9 million tons and US$ 1.09 billion, respectively and the conversion of agricultural areas to non-agricultural areas was 96,512 ha year^-1 (Mulyaniet_al2017, Statistics Indonesia, 2018). Alternative strategies are to intensify the areas between Melaleuca cajuputi stands and reduce nitrogen loss (NL) (Alam et al., 2020, Suryanto et al., 2020).
 
Nitrogen plays a role in chlorophyll formation in leaves (Marschner, 2012). The problem with nitrogen fertilization is the low efficiency due to high NL (Zhao et al., 2019). Biochar is an organic material formed from pyrolysis. Biochar can absorb CO₂ in the atmosphere, improve soil physical and chemical properties and increase inorganic fertilizer efficiency and crop yields (Coumaravel et al., 2011). Waste from the distillation of M. cajuputi leaves is a problem in Indonesia because of its enormous availability and un-utilization. M. cajuputi has the potential to be used as biochar and compost (Alam et al., 2020). Nurmalasari et al., (2020) reported that M. cajuputi biochar could increase the efficiency of urea fertilization by 18.22% while reducing N loss and increasing maize yield by 46.81% and 61.78%, respectively, compared with single urea application.
 
The deep placement application of 10 tons ha^-1 biochar made from M. cajupti waste of 100 kg ha^-1 ammonium sulfate produces soybean yield by 1.42 tons ha^-1 (Alamet_al2020). This value is still lower than the potential and actual yield of Grobogan varieties, which are 3.40 and 2.77 tons ha^-1, respectively (Indonesian Legumes and Tuber Crops Research Institute, 2016). The release rate of nutrients from fertilizers must be slower than that from fertilizers in which the nutrients are readily available for plant uptake. Use of nutrient briquette has the potential to increase fertilization efficiency and yield and reduce soil nutrient loss (Torne et al., 2017).
 
This study aims to evaluate the interaction of biochar briquette (BB) with ammonium sulfate fertilizer (ASF) for controlled NL in soybean intercropping with M. cajuputi.

The study was conducted in the wet season from November to February 2020 at Menggoran Forest Resort, Playen Forest Section, Yogyakarta Forest Management District, Indonesia. The average air temperature and relative humidity were 29.50 °C and 85.90%, respectively. The soil type was Lithic Haplusterts (Alam et al., 2019, Suryanto et al., 2020). The soil texture was dominated clay texture. CEC and pH H₂O were included in a very high category (58.78 cmol⁽⁺⁾ kg^-1) and alkaline category (8.16). The SOM (2.62%), total N (0.13%), available of P (7 ppm) and available of K (0.41 cmol⁽⁺⁾ kg^-1) were classified into the low category.
 
Experimental design
 
The experimental design was a randomized complete block design factorial with three blocks as the response surface methodology (RSM). The treatments included different levels of biochar briquette from M. cajuputi waste (0, 2 and 4 grain plant^-1 or 0, 5 and 10 tons ha^-1) and nitrogen fertilizer supplied by ammonium sulfate (0, 50 and 100 kg ha^-1) as independent variables.
 
Biochar was made from the waste of distilled M. cajupti leaves using the Kiln Traditional Method (Emrich, 1985). The process of making BB consisted of mixing, molding and drying. Each briquette weighed 10 g. The ASF used was from Zwavelzure Ammoniac (ZA) brand. The ZA fertilizer used in this study contained 20.93% N-NH₄⁺ and 23.84% S-SO₄^2-. The pH(H₂O), C, H, N and O in the biochar briquette used in this experiment were 8.05, 738.8 g kg^-1, 23.2 g kg^-1, 1.7 g kg^-1 and 22.58 g kg^-1, respectively (Alam et al., 2020).
 
Soybean variables
 
The observation parameters were nitrate reductase activity (NRA) (Krywult and Bielec, 2013), total chlorophyll (TC) (Gross, 1991), leaf photosynthesis rate (LPR) (Li-Cor, 1999), nitrogen loss (NL) (Fageria, 2014), nitrogen use efficiency (NUE) (Rathke et al., 2016) and seed yield (SY) (Alam et al., 2019, Suryanto et al., 2020).
 
Statistical analysis
 
The RSM equation used in this experiment applied the uncoded independent variables as follows (Koocheki et al., 2014, Myers et al., 2009). The fitted model was an evaluation by the R², RMSE and lack-of-fit. The lack-of-fit criterion used in this study was that the significance of lack-of-fit tested with a F-test should be less than 5% (Myers et al., 2009). The optimum levels of BB with ASF were calculated under the economy scenario using the SY variable and estimation with ridge regression (Koocheki et al., 2014, Marquardt and Snee, 1975). All analyses were performed using PROC RSREG in SAS 9.4 (SAS Institute, 2013).

Fitted models for soybean variables
 
RSM is one of the statistical methodologies used to obtain optimum results (Myers et al., 2009). The lack-of-fit test was used to evaluate the quality of the fitted model. The lack-of-fit test was not significant for all soybean variables so that all models were fitted to use (Table 1).
 

 
Estimated response for soybean variables of experimental factors
 
An interaction was found between BB with ASF in all soybean variables (Table 1). The applications of BB and ASF significantly increased NRA. BB showed a linear pattern, whereas ASF showed a quadratic pattern (Table 1). The applications of 4 grain plant^-1 BB with 100 kg ha-1 ASF produced the highest NRA by 3.86 μmol NO_2- g^-1 h^-1 (Table 2). NRA showed a positive correlation with ammonium and nitrate content in the soil (Loussaert et al., 2018). Purbajanti et al., (2016) reported that 100 kg ha^-1 ASF increases NRA content by 120.88% compared with that without ASF.
 


The applications of BB and ASF significantly increased TC. The BB showed a linear pattern, whereas the ASF showed a quadratic pattern (Table 1). The treatments of 4 grain plants^-1 BB with 100 kg ha^-1 ASF produced the highest TC value by 0.69 g g leaf^-1 (Table 2). Solanki et al., (2018) informed that integration between organic with inorganic fertilizer increases the chlorophyll content in leaves compared with that without fertilizer and a single application of inorganic fertilizer.

The applications of BB and ASF significantly and very significantly increased the LPR. The BB and ASF showed quadratic patterns (Table 1). Treatments of 4 grain plant^-1 BB with 100 kg ha^-1 ASF showed the highest LPR of 437.72 μmol CO₂ m^-2 s^-1 (Table 2). Increased photosynthesis capacity contributed to an increase in biomass and yield. The application of biochar increased the photosynthesis rate and the WUE in potatoes (Akhtar et al., 2014). Increased N fertilization into the soil significantly increases stomatal conductance, transpiration rate, intercellular CO₂ concentration and soybean growth (Zhang et al., 2013).
 
BB significantly increased NL, whereas ASF very significantly increased NL. The regression patterns of BB and ASF were quadratic (Table 1). The applications of 0 grain plant-1 BB with 100 kg ha^-1 ASF showed the highest NL of 35.60 kg ha^-1 (Table 2). The integration between organic and inorganic fertilizers is useful for increasing N uptake, NL and maize yield (Dunjana et al., 2012). Increased N fertilization showed a significantly positive correlation with increased N loss through the leaching process, namely, 187.50% nitrate and 28.10% ammonium (Zhao et al., 2019).

The BB treatment did not significantly increase NUE, whereas ASF very significantly increased NUE. BB and ASF showed quadratic patterns (Table 1). The applications of 4 grain plant^-1 with 100 kg ha^-1 showed the highest NUE of 6.53 kg grain kg N_fertilizer^-1 (Table 2). Biochar can increase plant growth and yield, as well as NUE, by rising the CEC and sustaining the water holding capacity in the soil (Hagner et al., 2016). A positive relationship was established between N fertilizer and increased NUE. Biochar exerts a positive influence on plant growth by increasing NUE (Clough and Condron, 2010). NUE has a positive correlation with N application in the soil. Fertilization of N under optimum conditions maximizes NUE (Abebe et al., 2017).
 
The applications of BB and ASF very significantly increased SY. The treatments of BB and ASF showed quadratic patterns (Table 1). Under the treatments of 4 grain plant^-1 of BB with 100 kg ha^-1 ASF showed the highest SY of 1.568 ton ha^-1 (Table 2). Kanouo et al., (2018) reported that biochar has the potential as a soil amendment on degraded soil while increasing the legume yield by 40% and total biomass by 25%. The addition of NH₄⁺_-N is significantly correlated with the increased soybean yield intercropping with kayu putih (Alam et al., 2019).
 
RSM revealed that the optimum dose of 3.70 grain plant^-1 or 9.25 tons ha^-1 BB with 76.31 kg ha^-1 ASF yielded the maximum NRA, TC, LPR, NL, NUE and SY values of 3.73 μmol NO₂^- g^-1 h^-1, 0.67 g g leaf^-1, 428.82 μmol CO₂ m^-2 s^-1, 21.31 kg ha^-1, 5.93 kg grain kg N_fertilizer^-1 and 1.44 tons ha^-1, respectively (Figs 1a, 1b, 1c, 1d, 1e, 1f). Coumaravel et al., (2015) informed that the application of biochar combined with NPK fertilizer can increase the sustainability of soil fertility and maize productivity.
 

 
The theory behind the briquette is that a smaller surface area to volume ratio of briquette can significantly reduce N loss through ammonia volatilization (Torne et al., 2017). Urea applied on the surface can reach N loss as high as 35%. However, buried briquette only lose approximately 4% N, which is a considerable improvement in NUE (IFCD, 2013).

A positive interaction was found between BB from M. cajuputi waste with ASF for all soybean variables. The optimum values were 3.70 grain plant^-1 or 9.25 tons ha^-1 BB and 76.31 kg ha^-1 ASF reduced the use of ASF by 23.69% and increased NRA, TC, LPR, NL, NUE and SY by 6.09%, 6.25%, 4.07%, -38.25%, 19.07% and 13.02%, respectively, compared with the single application of ASF.