Soil chemical properties
Data from the chemical analysis of soil, namely pH, C, N and C/N ratio before treatment and 60 days after treatment with organic mulches are presented in Table 1.
Soil pH
The results of the statistical analyses demonstrated that soil acidity (pH) in treatments with RSM, RHM and SDM were not significantly different (p>0.05) from control (NM). As shown in Table 1, there is a slight increase in soil pH value after the application of organic mulch from rice straw, rice husk and sawdust as compared to control, where the average acidity level is pH 6. A stable soil pH value is around 7.0
(Pan et al., 2014), while a pH below 7 is acidic and a pH above 7 is basic or alkaline. Most plants require pH between 5.5 and 7.0, but some other plants can grow and adapt beyond the optimum pH (
Salahudeen and Sadeeq, 2018). Soil acidity (pH) is directly and indirectly affected by changes in soil communitystructure
(Zhang et al., 2021) in the form of nitrogen fixation, ammonification, nitrification and denitrification with the participation of certain microorganisms
(Hasan et al., 2019).
Carbon (C)
Based on the statistical analyses, the average C content of the soil (Table 1) in treatments with RSM, RHM and SDM resulted in significant different results (p<0.05) as compared to control (NM), organic mulch with rice straw, rice husk and sawdust can increase the C content of the soil. This increase is influenced by organic matter from mulch containing carbon which can be utilized by soil microbes. Among all mulches sawdust takes the longest time decompose because of its high C/N ratio and nutrient status. These findings confirm by
Peera et al., (2020) reported that sawdust contains high amounts of carbon and nitrogen and is prone to clumping, making it take long time to decompose compared to other mulch materials. According to
Bajoriene et al., (2013), organic mulches in the form of sawdust and rice straw are able to increase the C-organic content of the soil.
Lalruatsangi et al., (2018) also stated that organic mulches from rice straw and rice husk also contain carbon that can increase the population of soil microbes such as bacteria and fungi. C-organic content contributed to the soil in the decomposition process of organic mulch can help to improve soil structure.
Nitrogen (N)
The average N content value of the soil (Table 1) indicates that treatment with SDM is significantly different (p<0.05) from control (NM), whereas treatments with RSM and RHM are not significantly different (P>0.05). Data presented in Table 1, indicated that the average N content in the sawdust mulch treatment is higher than control. The rice straw and rice husk mulch treatments also demonstrates slightly higher average value than the control, although not statistically different. The organic matter content of the mulch resulted in the nitrogen level of the soil through microorganisms. These results corroborate with the findings of
Paunovic et al., (2020) found that soil treated with sawdust mulch increase humus content (1.0%) and N content (0.05%).
Korkanç et al., (2021) also reported that organic mulch can affect soil nutrients and effectively prevent nutrient deficiencies and improve nitrogen availability.
C/N ratio
The results of the statistical analyses showed that the C/N content (Table 1) in treatments with RSM, RHM and SDM was not significantly different (p>0.05) from the control (NM), with the average C/N content in all organic mulch treatments being slightly higher than the control. Carbon and nitrogen contents are the main components of organic matter for soil fertility (
Swangjang, 2015). The quality of organic matter is determined by the ratio of carbon to nitrogen (C/N ratio) which is related to the utilization of organic N by plants as mineral N. After the decomposition of organic matter, soil microorganisms use nitrogen for enzyme production and growth.
Abbasi et al., (2015) revealed that the mineralization process of nitrogen can occur at a C/N ratio below 15, while N inhibition occurs if the C/N ratio is above 25. The C and N content and lignin in the soil are the main drivers of the C/N ratio which affects soil quality, soil biology and the activity of decomposing microbes
(Mueller et al., 2015). Therefore, the selection of raw materials for organic mulching must pay attention to the C/N ratio, which ranges from 30:1 to 80:1 without acidic or alkaline, non-toxic and abundant materials
(Peera et al., 2020).
Effects of organic mulches on weeds
Table 2 showed data pertaining to weed population, fresh weight and dry matter across all treatments, wherein treatments involving RHM and SDM exhibit statistically significant differences (P<0.05) from the control treatment (NM). The average values of weed population, fresh weight and dry matter in plots treated with rice straw, rice husk and sawdust mulches were lower than those without mulch. This proves that organic mulch can suppress the growth of weeds around Super napier grass plants. These findings support previous studies which have proven that straw mulch and other organic mulches are successful in controlling weeds in the cultivation of lentil and other crops (
Verma and Pradhan, 2024;
Rhioui et al., 2023) and blocking the light that weeds need for photosynthesis
(Iqbal et al., 2020).
The results showed that the highest percentage of weed index and weed efficiency control was found in the SDM treatment (Table 2). Organic mulch is able to suppress weeds, as shown by the percentage of weed index and weed efficiency in the control, which reached 83% and 88.92%, respectively, especially in the SDM treatment. According to
Kumar et al., (2021), Organic mulch is effective in reducing weed growth with an average organic mulch weed efficiency control of 70% and resulted better crop growth. Organic mulch are effective alternatives for suppressing weed growth by 70-95% and tilling the soil between crops without using chemicals
(Mairata et al., 2023).
Effects of organic mulches on the growth of super napier grass
Table 3 shows that the plant height and stem length of Super napier grass in plots treated with RSM, RHM and SDM are significantly different (p<0.05) from the control (NM). Organic mulch maintain water content, prevent evacuation and increase soil nutrients, thus helping the growth of Super napier grass. These findings are in line with the results of
Utamy et al., (2012) reported that weed control management resulted in significant effect on plant height and tiller density of dwarf Napier grass. Another study by
Thakur and Rakesh (2021) also found that organic mulch increase plant height. In this study, the average plant height was found to be higher at 60 days after treatment, where RHM recorded significantly highest forage yield which was followed by highest yield, followed by RSM and SDM, while the lowest yield was obtained from the control (NM).
Data on the length and width of Super napier grass leaves in Table 3 showed that treatments with RSM, RHM and SDM are significantly different (p <0.05) from the control (NM). This indicates that these organic mulches influence the growth of Super napier grass. In line with
Verma et al., (2022) stated that organic mulch treatment produces plants with excellent growth rates in higher average plant height and dry weight compared to the control. According to
Shashikanth et al., (2022), organic mulch can improve growth attributes since it helps maintain soil water content, allowing the plant to absorb water. Mulch also prevents soil erosion and has a good impact on soil microbes, nutrient balance and plant growth
(Iqbal et al., 2020).
As displayed in Table 3, the results of the analysis of the number of leaves are not significantly different (p>0.05) in all treatments, with the highest average number of leaves obtained in the RHM treatment. These findings confirm the results of a study by
Ikhsan et al., (2022) that treatment with rice straw mulch does not significantly influence the number of leaves of the plant. The results of another study by
Pangaribuan et al., (2023) also indicate significant impact of rice straw mulch and cow urine on plant height, number of leaves, leaf greenness and N nutrient uptake. The number of tillers in plots treated with RSM and RHM is higher than those treated with SDM and NM. Treatment with sawdust mulch results in a smaller number of tillers because the hardened sawdust inhibits the growth of some tillers. This is in line with
Peera et al., (2020) stated that sawdust contains high amounts of carbon and nitrogen which makes it easy to harden. In contrast, the results of
Utamy et al., (2012) showed that the number of tillers increased significantly over time with paper mulch.
Yang et al., (2020) also reported that mulching wheat plants can increase the number of tillers, as evidenced by the higher tillering capacity (TC) in mulch-treated plots compared to untreated plots.
Effects of organic mulches on the production of super napier grass
As shown in Table 4, the average fresh weight production of Super napier grass (kg/plot) is not significantly different in all treatments, with the fresh weight of stems in plots treated with RHM, RSM and SDM being higher than the control (NM). Meanwhile, the fresh weight of leaves in the RHM treatment shows significant difference compared to control (NM). The production of fresh weight and dry matter of Napier grass increases as the plant ages
(Samarawickrama et al., 2018). The biomass production yield of Super napier grass aged 70 days is 60 tons/ha
(Liman et al., 2020).
The results of the dry matter of the stems and leaves of Super napier grass are not significantly different in all treatments (Table 4). The dry matter production of the stems and leaves of Super napier grass in the RSM, RHM and SDM treatments is found to increase, even though not significantly different from the control (NM). Increase in the dry matter of Super napier grass is influenced by the contribution of mulch organic matter which can increase soil nutrients through decomposition by soil microorganisms. In addition, mulch can retain soil moisture and suppress weed growth around plants, positively affecting the main crop. Even though it is not commonly used in the cultivation of grass, the use of mulch in controlling weeds have positive impact on the growth and dry matter content of dwarf Napier grass
(Utamy et al., 2014). The dry matter of Napier grass will increase as the plant and the accumulation of fibrous tissue and cell wall structures increases
(McDonald et al., 2022). Dry matter production is a vital indicator of forage production as it is considered a representation of all processes and events that occur in plant growth
(Budiman et al., 2012).