Trass Effect as a Source of Silicon on Soil, Hay, Husk and Growth of Rice Plants

Silicon (Si) is one of the important things for rice growth. The importance of Si relates to increased rice yield, increased resistance to disease and resistance to falling. The rice is an accumulator plant of Si which requires Si for its growth. However, the Si in soil is continually decreased therefore the additional Si is needed into the soil. Trass is one of the natural materials containing Ca and Si, therefore it can be used as a Si fertilizer. This study aims to determine levels of soil Si, straw, husk, and growth in rice. This research consisted of three types of soil, Oxisol, Inceptisol and Vertisol as the main plot and 7 doses of burnt fuel namely 0 (D0); 1.25 (D1); 2.5 (D2); 3.75 (D3); 5 (D4); 7.5 (D5); 10 (D6) g kg-1 of soil as subplots. The treatment which is using in this research is a combination of the two factors and repeated 3 times 63 unit experiments were obtained. The results showed the Trass significant concerning to Si in the husk and Si of the soil. Vertisol gives the highest number of panicles of 27 and Si in the straw of 12.75 mg kg-1.


Introduction
Rice (Oryza sativa L.) is one type of food plant which has the important role in Indonesia society, therefore the need for rice in Indonesia has increased from year to year along with the increasing population. The consumption of rice per capita in Indonesia necessary is around 111.58 kg year -1 , in order that 29.13 million tons of rice is essential by Indonesia each year [1].
Many efforts have been made to meet domestic demand for rice. In other hand, several problem cause the need for rice itself not to be fulfilled. The conversion of agricultural land to non-agricultural land [2] and land degradation causes macro and micronutrients as well as beneficial elements such as low Si so it does not support rice growth [3]. Rice needs Si in its growth because as much as 230 -470 kg ha-1 Si is needed by rice per plant [4]. In other hand, rice soils generally have a low Si content [5,6]. This can be proven by seeing farmers the erosion of nutrients land use without proper management practices, resulting in depletion of losses in soil and resulting in reduced yields [7,8,9]. Si has an important role in rice, increasing plant resistance to disease, stress or environmental stress to disease, and reducing metal toxicity [11,12,13,14,15]. This shows that Si can be an element essential needed for rice growth and production [16]. Currently, Si ranks fourth as the most important nutrient for rice in rice-producing countries in Southeast Asia after N, P, and K [17]. In hence, the management efforts are needed to which can restore or maintain levels therefore the remaining harvest is in the form of husks and straw or the addition of Si fertilizer [18,19]. One thing which can be used as Si fertilizer is Trass.
Trass is formed from weathering of volcanic rocks which are rich in feldspar and silica [20]. Indonesia has many areas which hold Trass potentials such as Bogor, Nagrek, Yogyakarta, and Pekalongan. Trass is also available outside Java Island such as Gianyar, Lampung, Flores Island, Minahasa in North Sulawesi, and Southeast Sulawesi [21].
It is usually used as a building block for concrete therefore other functions of trass which can be used as fertilizer for Si have not yet been widely used. In this study, the trass test was carried out as a source of Si and its effect on plant growth.

Place and time of research
The research was conducted at the Laboratory of Chemistry and Soil Fertility apart from that it was also done the Greenhouse of the Cikabayan Experimental Garden, Department of Soil and Land Resources, Faculty of Agriculture, Bogor Agricultural University. The research for seven months from January to September 2017.

Materials and Tools
The materials used were three types of wetland Oxisol from Mount Sindur, Inceptisol from Ciampea Bogor, and Vertisol from Cihea Cianjur [9]. The trass used comes from Ciampea Bogor which is combined with CaCO3 as a source of silica fertilizer. The basic fertilizers used are urea, SP-36, KCl, and other materials for analysis in the laboratory.

Research procedure
The greenhouse experiment done used a factorial randomized block design consisting of two factors. The first factor is three types of soil, namely Oxisols (S1), Inceptisols (S2), and Vertisols (S3). The second factor consists of seven levels of trass burn dose, namely control (D0); 1.25 (D1); 2.5 (D2); 3.75 (D3); 5 (D4); 7.5 (D5); 10 (D6) g kg-1 and repeated three times to obtain 63 experimental units. Greenhouse experiments were carried out to determine the effect of trass on plant result, namely the number of panicles, Si content in the soil, husks, and straw.
Air-dry the soil from the field while mashing it until it passes the 5 mm sieve. Furthermore, the soil is weighed 5 kg absolute dry weight (BKM) and put in a bucket, then the trass is given into the bucket according to the treatment dose and stirred until it is evenly grounded. Subsequently incubated for seven days in the inundation conditions ± 5 cm. After the incubation period ends, followed by is carried out.

Planting and Maintenance
For 20 days old, 3 seeds are planted in each pot. The basic fertilizers given are Urea, SP-36, and KCl which is supplied according to the recommended dosage, namely 0.6 g Urea kg-1, 0.2 g SP-36 kg-1, and 0.2 g KCl kg-1. Urea and KCl were given three times, namely at planting time, 2 MST, and maximum vegetative time (10 MST). SP-36 is given once during planting. Stagnant water conditions of ± 5 cm were maintained throughout the experiment. Weeding is done manually to weeds are found by removing them. Pest control is carried out as necessary with insecticide beta siflurine. At 10 WAP measurements were taken to calculate the number of tillers and plant height.

Harvest
Harvesting is done when the rice reaches the yellow cooking criteria, namely 90% of the panicles have turned yellow. This condition is reached about 35 days after flowering, which is 120 days. Harvesting is done by cutting the rice stalks just above the soil surface, the grain is knocked down, weighed and dried to get the weight of milled dry grain.

Result and Discussion
Soil analysis was carried out to determine nutrient levels in the soil before being applied the treatment ( The results of the analysis of variance showed that the soil type had no significant effect on the number of panicles 10 MST, while the type of soil combined with trass too no significant effect. The Duncan test results stated that the effect of trass and soil type on the number of panicles (Table 2) showed that the number of panicles in Vertisol (S3) was higher than Oxisol (S1) and Inceptisol (S2). The presence of Si is sufficient to strengthen the stems, help form panicles, increase the number of panicles and the percentage of ripe rice grains, and maintain upright leaves [22]. Vertisols with high Si content in the soil and coupled with trass as the Si source help to increase plant growth. Oxisol is a type of soil which has undergone further weathering and has a limiting factor, namely the low level of soil fertility [23]. This is evidenced by the results of the initial soil analysis (Table 1), Oxisols have a lower fertility rate than other soil types. Inceptisol is soil with moderate Si nutrient content which has Mn content of 61.15 ppm, Fe 23.42 ppm (Table 1). This is thought to be a limiting factor in rice growth. The results of variance analysis showed that soil type had no significant effect on rice straw Si content, while soil type combined with trass too no significant effect. The Duncan test results stated that Vertisol (S3) had the highest Si content in straw compared to the other two soils (Table 3). Si content in rice straw ranges from 4-20% [24]. This is the result of the Si analysis carried out on the husks. In addition it can be seen that in Vertisol (S3), the increase in each dose of trass given also making the increase of Si level in the straw. The provision of adequate Si fertilizers causes an increase in the absorption of Si by rice and subsequently, the Si content in straw also increase [25].
In addition, it can be seen that in Vertisol (S3), the increase in each dose of trass given, the Si level in the straw also increase. The provision of adequate Si fertilizers causes an increase in the absorption of Si by rice and subsequently, the Si content in straw also increases [25]. The results of the variance analysis showed that there was an interaction between soil type and trass against Si in rice husks. However, it can be seen that Vertisol has a lower Si content in the husk. This can be caused by the very high Fe content in Vertisols compared to the other two types of soil. The rice husk is usually around 10%, but in this study, it produced up to 38.77%, therefore the return of plant residues to the soil can help restore Si which has been lost during planting [26,27,28]. The harvest of 5 tons of grain ha-1, 4.5 tons of straw and husks covers 30% of the grain weight, in hence in one harvest in the rice fields of Lembur Leutik hamlet (behind the Darmaga IPB campus, West Java) 971 kg of SiO2 will be transported ha -1 [29]. The SiO2 content of husk and rice straw in this area was 21.23 and 16.01%.
Based on table 4, it can be seen that the increasing dose of trass, the higher Si content in the soil. Increasing the dose of trass increases the available soil Si because the H4SiO4 from the trass dissolves into the soil, so the soil Si concentration increases. This proves that Si fertilization is needed in rice fields in Indonesia. As previously known, Si is a very abundant element in the soil with a range of 25 to 35%, repeated planting without the addition or addition of Si can reduce the available soil Si content [29]. In Indonesia, the soil Si content is lower in rice fields that are intensively planted where the very large Si uptake is not followed by a return of harvest residues or the addition of fertilizers [3]. Noted: The number followed by the same letter in the same column shows that it is not significantly different at the level of α = 5% with Duncan's continued test.
In this study, the application of Si fertilizer caused the higher Si uptake in rice biomass (grain + straw) compared to the control. Lack or sufficiency of Si in the soil is mainly determined by the speed at which it is filled in the soil solution and its absorption during plant growth. This is consistent with the statement of Jawahar & Vaiyapuri (2013) that Si uptake in plants depends on the ability of the soil to supply Si [30].
The summary of Si in general is that Si fertilization can increase Si availability when the Si content is low in the soil. Si which is given through fertilization can increase the availability of Si in the soil and Si uptake in straw and grain [25].

Conclusion
1. Trass has a significant effect on the Si content in the husk and Si of the soil. Vertisols gave the highest number of panicles, namely 27 and Si in straw at 12.75 mg kg -1 . 2. Returning plant residues to the soil is very helpful in restoring or maintaining Si in the soil.