Improved black soybean performances grown on selected highly weathered soils by using bio-nano-ortho silicic acid

The objectives of the study were to determine the potential use of bio-nano-ortho silicic acid (OSA) originated from locally mineral enriched with silica-solubilizing microbes to improve yield, reduce chemical fertilizer dosage, and increase water use efficiency (WUE) of black soybean grown on selected highly weathered soils. The first-year (2017) study was conducted at Majalengka and Natar area and arranged in a random block design (RBD) with three replicates, using a Detam-1 variety. Treatments of NPK fertilizers were 0, 50, 75, and 100% of standard recommended dosages in combination with 0, 2, 4, and 6 L bio-nano OSA Ha−1. In general, application of 4 L bio-nano OSA Ha−1 saved 32% NPK fertilizer dosage and improved growth and yield of Detam-1. The second year (2018) trials consisted of no fertilization (P0), farmer standard NPK fertilization (P1), P1 + organic matter (P2), 4 L bio-nano OSA Ha−1 + NPK (P1), 50% (P3); and 75% (P4) respectively, arranged in a RBD with three replicates at three regions, i.e. Majalengka (Alfisols), Natar (Ultisols), and Indramayu (Alfisols). The results confirmed that the application of bio-nano OSA at 4 L Ha−1 improved nutrient use and WUE as well as yield of Detam-1 on all three soils studied.


Introduction
Among main commodity crops in Indonesia, soybean is the third biggest consumed agricultural crop after rice and corn. However, national production so far is still deficit to satisfy the needs and therefore import is one most immediate option. Low productivity and/or limited growing area are two main factors causing this phenomenon. On the other hand, a considerably large area is available for development of soybean, such as those in Lampung [1] and West Java, especially for black soybean to supply the growing soy-sauce industry in these regions which are dominated by highly weathered soils [2]. The use of so-called marginally suitable non-irrigated soils for agricultural crops will face a major constraint, i.e. intensive drought period due to excessive evapotranspiration [3] [4]. On top of that, strong soil acidity plays important role on aluminum (Al) saturation capable of nutrient adsorption especially phosphate (P) [5]. On the other hand, silica (Si) has been shown to be able to improve plant drought tolerant as it controls stomata openings, and competes in Al adsorption releasing P available for plants [6] [7]. Reference [8] found that plants adsorb Si as much as other macro nutrients although it has not been considered as a macro nutrient yet. It has been reported also that Si readily available to plant is in the form of silicic acid (H 4 SiO 4 ) or mono-silicic acid [Si (OH) 4 ] only [9] and soil Si solubility depends on particle size of bearing material [3]. This is the reason why in highly weathered soils with relatively high Si content show positive response on Si fertilizer as the soil Si is mostly In order to provide with an efficient technology, a newly constructed Si fertilizer formula was introduced in combination with Si-solubilizing microbes [10] and evaluated on black soybean grown on three different highly weathered soils in Lampung and West Java, Indonesia. The formula socalled bio-nano-ortho silicic acid (bio-nano OSA) was derived from quartz sand originated from Bangka-Belitung islands containing > 5% H4SiO4 with average particle size of 18 nm [11] [12]. Previous results indicated that the application of the bio-nano OSA improved drought tolerant of oil palm seedlings [13], growth and yield of mature oil palm in Central Kalimantan [14]. By using 4-6 L Ha-1 of bio-nano OSA the yield of black soybean improved 36.7%, reduced 32% chemical fertilizer dosage, and tended to increase water use efficiency (WUE) up to 65% [15]. This article reports the effects of bio-nano OSA application on the yield, nutrient use, and WUE of a Detam-1 black soybean variety grown on Natar Ultisols (Lampung), Jatitujuh Alfisols (West Java), and Bantarwaru Alfisols (West Java).

Materials and Methods
This paper reports a two-years field experiments in Natar, Lampung Tengah, Lampung, and Jatitujuh, Majalengka, West Java, in 2017 and with an additional area in Bantarwaru, Indramayu, West Java, in 2018, on Ultisols and Alfisols soils. According to Soil Taxonomy [16], the Ultisols of Natar and belongs to Udults, whereas Alfisols of both Jatitujuh and Bantarwaru shows a vertic characteristics, i.e. significant cracks during dry season. The soils used were food crop (Natar), sugarcane (Jatitujuh), and rice field (Bantarwaru) area.

Materials
Bio-nano OSA was prepared by using method reported earlier containing 9% H 4 SiO 4 which enriched with selected Si-solubilizing microbes, i.e. Aeromonas punctata, Burkholderia cenocepacia, B. vietnamiensis, and Aspergillus niger [10] [11]. Black soybean variety used was Detam-1 originated from Balitkabi, Malang. Liming with CaO was applied prior to planting. Urea, TSP, and KCl were single NPK fertilizers used in these experiments. To enhance seed germination and rhizobium infection, the Detam-1 seeds were inoculated with RhiPhosAnt, a commercial rhizobium inoculant enriched with P-solubilizing microbes [17].

Methods
The bio-nano OSA was prepared by employing the method described earlier by . A randomized block design was used to examine six treatments with three replicates and plot size of 300 m 2 . The treatments consisted of (i) blank/untreated (P0), (ii) NPK farmer standard practice (P1), (iii) P1 + 2 ton farmyard manure Ha -1 (P2), (iv) 50% P1 + 4 L bio-nano OSA Ha -1 (P3), (v) 75% P1 + 4 L bio-nano OSA Ha -1 (P4), and (vi) 100% P1 + 4 L bio-nano OSA Ha -1 (P5). Black soybean var. Detam-1 was sown in hole at 40 cm x 20 cm planting distances which has been limed previously with 500 kg CaO Ha -1 (equivalent to 1500 kg dolomite). Standard fertilization used was 75 kg urea + 100 kg TSP + 100 kg KCl and applied two weeks before planting. The soybean seeds were inoculated with N-fixing and P-solubilizing microbes by using a commercial product, i.e. RhiPhosAnt, to enhance initial plant growth [17] [18]. Bio-nano OSA was applied twice by spraying to the soil after diluting the formula 100x with fresh water at 28 and 45 day after planting (DAP). Standard crop maintenance was performed including weed, pest, and disease control during the experiment period. Parameters observed include growth and yield of the plants as well as the water consumption and water use efficiency (WUE). General soil analyses were performed prior and after experimentations by using standard methods described by [19] [20]. A ring sample was taken at harvest day to determine water contents at different suction pressures to set a pF curve of each treatment plot.
Water consumption was determined based on evapotranspiration data following [21]  water content at field capacity WCpwp: water content at permanent wilting point and WCsat : water content at saturated condition. Potential evapotranspiration (ETo) data was determined from climatic data for the last four months and calculated by using FAO-CROPWAT 8.0 computer program [25] [26]. Plant transpiration of each plot was measured using a porometer at 58 days after planting [27] [28] [29]. Water use efficiency (WUE) was calculated based on the volume of water used by the crop to produce a unit weight of black soybean yield employing the formula described by [30] [31].

Results
During the first-year activity, a simpler production technology of bio-nano OSA yielding min. 5% of OSA content was successfully developed and further enriched with selected SSM as bio-nano OSA formula. The trials reported here are from second year results and indicated that bio-nano OSA improved the yield of Detam-1 (Figure 1-3). In general, application of 4 L bio-nano OSA Ha -1 saved 32% NPK fertilizer dosage, particularly on Jatitujuh and Bantarwaru Alfisols. On the other hand, the pattern was a bit different on a less fertile soils, i.e. Natar Ultisols. The lower yields obtained from Jatitujuh experiment was due to an intensive dry season when the trial commenced. However, the results confirmed that the application of bio-nano OSA at 4 L Ha -1 improved nutrient use and WUE as well as yield of Detam-1 black soybean on all three soils studied. The improved efficiency in nutrients used are shown especially in Jatitujuh ( Figure 1) and Bantarwaru (Figure 3) where the optimum yields were achieved at 32 and 49 % reduced dosages of NPK, respectively. Black soybean drops in Jatitujuh required water higher than the other two areas under P0-P3 treatments and lower corresponding WUE values (Table 1). However, the addition of bio-nano OSA at 4L Ha -1 dosage improved their WUE values when combined with 25% reduced NPK fertilizer dosage or with 100% dosage of the fertilizers.

Discussion
All soils used in this experiment were acidic in reaction with very low water-soluble Si (H 4 SiO 4 ) contents (< 5 ppm). In comparison, agricultural soils in South Korea are freed from Si fertilizer application is when the plant-available Si above 157 ppm. Therefore, it is understood that the Si addition on these three soils with very low available Si-contents responded positively to Si application. Si has been considerably long understood of having several benefits on improving nutrient efficiency, especially when it competes for aluminum (Al) in the soils, then it will free phosphate and become readily available to plants In addition, the role of Si in controlling stomatal openings have been widely reported [15] which in turn leads to a lower evapotranspiration rate as indicated by a more efficient WUE. These evidences were then assumed to benefit the plants in absorbing other nutrients, i.e. nitrogen (N) and potassium (K) so then the dosage of chemical fertilizers could be reduced significantly without affecting yield reduction [32].

Conclusion
The application of bio-nano OSA on an Ultisols and Alfisol soil under acidic in reaction with very low water-soluble Si (H 4 SiO 4 ), promoted better growth and yield performances of Detam-1 black soybean variety. Application of 4 L Ha -1 bio-nano OSA can reduce NPK fertilizer dosages up to 50%. However, further study is needed to confirm these results, under different location or ecosystems and a wider application.