Effect of Municipal Solid Waste compost Treatment on Physico-Chemical Properties of Garden Soil

In the present study amendment of three types of compost made from lemon peels (LP), vegetable waste (VW) and cook food waste (CF) in garden soil was carried out. It was observed that pH in all the treatments increased from control with a maximum in LP with 22% and minimum in CF with 10% at 270 days.The soil temperature was higher than control with a maximum increase of 52% in CF and minimum of 20% in VW at 90 days. A maximum increase of OC was observed in CF compost treated soilwith 106% followed by LP with 64% and 24% in VW at 90 days.TN increased from control upto 90 days with 484, 100 and 46% rise in CF, VW and LP respectively. AP and AK also showed a very high increase rate with maximum of 551% in CF and 703% in LP respectively.


Introduction
During recent decades, the generated amount of solid wastes has exponentially increased almost all over the world due to population growth. It was estimated that about 2 billion tons of solid waste were generated in the world's cities during 2016 (World Bank 2019). Compost is made from decomposition of plant and animal remains with the objective of recycling the waste for crop production. The decomposition process during composting converts potentially toxic or putrescible organic matter into a stabilize state which can improve soil quality for plant growth (Adugna 2016). Compost has other bene cial effects, including diverting land ll wastes to alternative uses, removal of pathogens, residues of pesticides and control soil erosion. Compost can improve the capacity to produce safe "clean green" agricultural produce and importantly increase the potential for largescale organic food production (Paulin and Peter 2008). It contains organic matter providing nutrients to the soil, improves water holding capacity and good aeration providing favorable condition for germination of seeds and root development of crops (Edwards and Hailu 2011).
Soil micro and macro organisms rely on the availability of soil organic matter, therefore, organic amendments protect the soil biodiversity, the functioning of soil processes and the ecosystem services (Siedt et al. 2021).In general, the feedstock material of composts largely determines the quality of the mature compost. Most of the nutrients available from the feedstock materials are consumed by microbes during composting, and are then found in organic forms. Only about 15% of N in mature compost is available in the rst year after application, consequently composts are usually not su cient as the only measure for the management of N in the eld (Amlinger et al. 2003). However, due to reduced availability of N-forms in compost, nitrate leaching from soils after compost amendment is reported to be lesser when compared with soil treated with mineral fertilizers (Diacono et al. 2010). Therefore, higher application rate of composts reduces level of groundwater contamination (Erhart et al. 2007). Based upon the types of organic waste generated in different locations, composts having varied quality can be produced. In the present study composts derived from lemon peel, mixed vegetable waste and cooked food waste were selected and amended with garden soil. The change in the physicochemical properties of soil was evaluated in order to investigate the impact of the three types of composts on soil quality.

Experimental design
Three different types of composts derived from lemon peels (LP), mixed vegetable waste (VW) and cooked food waste (CF) were selected for amendment in garden soil. The study was carried out in Mizoram University Campus located at 20°43'44"N latitude and 92°43'48"E longitude for 270 days during 2019 to 2020. The experimental design of composting and the quality of the composts were described in Lalremruati and Devi (2021).The garden soil used during composting was used for the amendment study. Three pits having length of 58cm, breath of 48cm and depth of 15cm were made for each type of compost amendment in a polyhouse. The removed soil were air dried and mixed with the composts (w/w) at a ratio of 1:1. The soil and compost mixture were kept in the pits. A plot without any treatment of compost was maintained as control (C). The experiment was laid out in completely randomized block design. The plots were sprinkled with water whenever necessary in order to maintain 30 to 35% moisture content throughout the experiment. The experiment was conducted for 270 days.

Analysis of soil
At an interval of 30 days 300g of the compost amended soil were sampled from each plot from a depth of 0-15cm in order to study the physicochemical properties. Soil sample from the control plot was also collected for the analysis. Three replicates were maintained for each sample totaling to 30 samples. Soil temperature was recorded using a Digital Thermometer at an interval of 30 days in each plot maintaining three recordings in each plot. The composts amended soil were air dried till constant weight, grounded and nely sieved (0.15mm) and evaluated for organic carbon (OC) using Walkley and Black's titration method (Anderson and Ingram 1993), total nitrogen (TN) by using Kjeldahl's digestion method (Bremner 1982), available phosphorus (AP) using molybdenum blue method in NaHCO 3 extract (Olson et al. 1954) and available potassium (AK) using Flame Photometer. pH was determined using fresh soil sample taking 1:2.5 compost amended soil :water using Digital pH Meter (Anderson and Ingram 1993).

Statistical Analysis
Analysis of variance (ANOVA) was used to nd variation between the physicochemical properties between the different composts amended soil and between the sampling days. Pearson's coe cient of correlation was evaluated to nd correlation between the different parameters. The statistical analysis was done using MS-Excel and SPSS.

Change in physicochemical properties
The initial pH in all the composts treated soil was acidic and higher than control (Table 1), with 5.45, 6.52, 6.62 and 6.92 in C, LP, VW and CF composts treatments respectively. During the treatment period it was observed that in all the three types of composts amendment there was no signi cant variation among the sampling days ( Fig.  1), although showing a rise till 120 days and a gradual declining pattern. Maximum increase was recorded in LP with 22% and minimum in CF with 10% (p<0.01) at 270 days (Table 2) with nearly neutral pH of 7.1 in LP and a minimum in CF compost treatment with 6.4(P<0.001).Compost that have a near-neutral or slightly alkaline pH with a high buffering capacity usually elevate pH of acid soils (Shiralipour et al. 1992). Lee  During the amendment period soil temperature in composts treated soils showed a higher level till 240days than control with a maximum range of 28.3 to 45.5 o C in CF and minimum of 28.0 to 38.5 o C in VW compost treated soil (Fig. 2). Soil temperature showed signi cant variation among the sampling days (P<0.001)and within the different treatments (P<0.001). At 30 days the increase in temperature was maximum in all the three treatments compared to control with 52, 24 and 20% increase in CF, LP and VW respectively (P<0.01). However, a gradual declining pattern was shown in all composts treatments. At 270 days soil temperature was lower than control in LP and almost similar with control in VW but in CF there was still a 2% higher rate than control. Deguchi et al. (2009) have stated, the main factors contributing to increase in soil temperature due to compost application was the decrease in amount of water drawn from the deeper layers which decreased evaporation. Reduction in evaporation results from reduction in bulk density of soil. Amlinger et al. (2007) have cited more absorbing capacity of solar radiation by the dark colored decomposed organic matter and humic substances contained in the compost. The increase in soil temperature was very high although a gradual decline was observed. The reason can be attributed to the high rate of compost application in the present study. A step to reduce the soil temperature can be, allowing the composts to stabilize for at least 30 days before application in eld.
OC was higher in all the composts treated soil compared to control in the initial quality (Table 1). Signi cant variation of OC was observed among the sampling days (P<0.001)and between the different composts treatments (P<0.001). Maximum range of 3.0 to 4.58% was recorded in CF compost treated soil and minimum in VW with 2.1 to 3.5%during the 270 days period. There was a gradual increase in the initial days, however a declining pattern was recorded till the end of the experiment (Fig. 3).Maximum increase of OC was observed in CF compost treated soil with 106% followed by LP with 64% and 24% in VW at 90 days (P<0.01). At the end of 180 days it was more or less similar with control in VW and LP composts treated soil. However, CF compost treatment showed increase of 2% at 270 days. Brown and Cotton (2011) reported an increase of OC in agricultural soils in California by 3 times due to treatment of compost in comparison to control soils. Riwandi et al. (2015) also reported an increase of OC at 2.76% due to application of compost. Total C increased upto 1.86gkg -1 from 0.76gkg -1 indicating a rise of 145% and it was positively correlated with microbial community composition(Lee et al. 2019). Application of compost leads to increase in soil organic matter thereby increased OC and providing more void space in soil. The organic matter has a lower density than the mineral fraction of soil which is also refer to as uff effect (Kranz et al. 2020).
There was a signi cant variation of TN among the treatments (P<0.001) and within the sampling days (P<0.01).
Compared between the three types of composts treatments initial TN was very high in CF with 2.98gkg -1 as well as throughout 270 days treatment. In CF the TN increased rapidly upto 60 days recording upto 6.36gkg-1 providing a maximum range of 2.7 to 6.36gkg -1 . Minimum range was recorded in LP with 1.15 to 1.89 gkg -1 . In the composts treated soils a comparatively higher level of TN upto 90 days with 484, 100 and 46% rise in CF, VW and LP (P<0.01) was recorded respectively. However, in LP and VW composts treatments a drastic decline started from 120 days which gradually equals with control at 270 days. However, at 270 days there was still 48% increase of TN in the CF compost treated soil. The high release rate of TN in CF compost can be attributed to the low initial C/N ratio. Similar observations on increase in TN due to treatment of food waste compost was reported by Kelly et al. (2020) with 11%. They also observed that compost derived from food waste provided more N bene ts than cow manure-derived composts and have greater nutrient value.
Initial AP was higher in the composts treated soils compared to control (Table 1). Signi cant variation of AP was observed among the sampling days (P<0.001) and within the treatments (P<0.001).A gradual increase in AP upto 60 days in all composts treatments was recorded (Fig. 5). Maximum was recorded in CF with a range of 43.42 to 121.03mgg -1 throughout the experiment. In VW it varied from 43.73 to 102.42mgg -1 and in LP it varied from 32.0to 108.3 mgg -1 . At 90 days a maximum increase of 787% in CF, 541% in LP and 532% in VW (P<0.001) was recorded followed by a gradual declining pattern. At 270 days there was still a very high increase rate with 551, 350 and 269% in CF, VW and LP treatments respectively. Kelly et al.(2020) reported a similar increase of 127% in AP due to treatment of food waste compost in soil. Manirakiza and Seker (2020) was reported an increase of AP by 48.7mgkg -1 in soil due to application of compost.
Initial AK was maximum in VW with 320mgkg -1 and minimum in CF with 80mgkg -1 . Signi cant variation of AK was also observed among the sampling days (P<0.03) and within the treatments (P<0.001). Maximum AK was recorded in VW with a range of 230.2 to 648.42mgkg -1 and minimum in CF with a range of 103.3 to 256.0mgkg -1 throughout the experiment (Fig. 6). Maximum increase of 1383% in VW and minimum of 207% in CF was recorded at 90 days. There was a gradual decline in all treatments however similar to AP at the end of 270 days the level of AK was still high with 703, 503 and 170% increase rate in LP, VW and CF treatments respectively (P<0.05). Manirakiza and Seker (2020) reported an increase of AK by 397 mgkg -1 with 2% application rate of compost due to high presence of potassium in compost which was later released into soil through microbial degradation. Akoijam et al. (2017) also reported a signi cantly higher level of AK in soil due to treatment of ower waste, sh waste and sugarcane bagasse.

Correlation among the soil characteristics
In LP compost treated soil OC showed signi cant positive correlation with AP (r=0.83;P<0.05) and AK (r=0.74;P<0.05) ( at a rate of 10Mg/ha/yr will save around 2282kg CO 2 equivalent green house gas emissions. Application of compost in agricultural elds reduced cost of managing solid waste, provides alternative to inorganic fertilizer and also serves the purpose of reducing impact of climate change.      Variation of organic C (%) in the composts treated soil and control. Variation of total N (gkg -1 ) in the composts treated soil and control.

Figure 5
Variation of available P (mgkg -1 ) in the composts treated soil and control.

Figure 6
Variation of available K (mgkg -1 ) in the composts treated soil and control.