Response of Coffee Husk Biochar on Growth of Faba Bean on Nitisol and Soil Nutrients

Soil fertility depletion and the associated soil acidity has become a serious problem to crop production in most highlands of Ethiopia Fortunately, such problems can be reclaimed by the application of biochar as soil amendments which can be sequestered in the soil for several years.A pot experiment was conducted to investigate the effects of biochar on soil properties, growth response and nutrient uptake of faba bean. The design employed was a randomized complete block with four replications. The parameters analyzed includes: Trace Metals using DTPA extraction, macronutrient using 1 N ammonium acetate (pH =7) extraction. Dry ashing method was used to determine nutrient uptake of plant samples. The studied soil and plant data were collected and subjected to analysis of variance and treatment means were compared at the 0.05 probability level using list significant difference test. The results revealed that application of biochar significantly improved growth of faba bean and soil nutrient content. The highest values for soil chemical parameters such as available phosphorus and exchangeable cations were obtained from the application of 20 t/ha CHB. Similarly, the highest growth performance of faba bean including plant height, leaf number, chlorophyll content, nodulation number, root and shoot biomass, uptake of N, P and K were recorded from biochar-amended soil. From this study, it can be suggested that the application of biochar could be an alternative promising amendment to lime for acid soil management and sustainable crop production. But, further investigations need to be continued under field conditions across different soil and crop types.

However, limestone material and fertilizer are relatively expensive and unaffordable to the farmers and the lime supply has limited in Ethiopia, can only amend exchangeable calcium, magnesium, and phosphorus. Due to this, researchers have recently started using biochar and organic fertilizer (compost and bio-fertilizer) as an alternative soil amendment mechanism. The biochar materials can increases crop yield, it's locally available, cheaper compared to limestone, chemical fertilizer and environmentally friend. So, the potential of biochar as a soil nutrient amendment, soil acid management in agricultural fields is a recently recognized and yet it is underutilized technology. Therefore, the aims of this study were, to test effect of the application of coffee husk biochar on nitisol 1) the response of faba bean growth (agronomic data) and nutrient uptake, 2) effect of soil nutrient properties.

Description of the Study Area
The study was conducted at Holetta agricultural research center in greenhouse and geographically located at 09 o N, 38 o E at an altitude of 2400 m above sea level and characterized with a mean annual rainfall of 1044 mm, mean relative humidity of 60.6% and mean maximum and minimum temperature of 22.1 o c and 6.2 o c, respectively. The dominant soils of the area are reported to be Nitisols which are sesquioxidic and moderately to strongly acidic [16].

Sample collection and preparation
Before sampling, there was done assessment for identification of exact area of the soil acidity problem by measuring soil pH in laboratory. Then for pot experiment and Pre-planting soil nutrients analysis composite soil sample (0-20 cm depth) at five points in zigzag pattern was collected using an auger, core samplers were used for bulk density sampling separately from the place of soil pH below 5. The collected sample kept in polyethylene bags. Coffee husk biochar was taken from Jimma University College of Agriculture and Veterinary Medicine and the collected soil and biochar sample were transferred to plastic trays and break up the large clods to speed up drying. The sample was air-dried, crushed with mortar and pestle and passed through a 2 mm opening stainless steel sieve [17].

Soil Physico-chemical Properties Analysis
All analytical measurement was performed in Agricultural Research Laboratory. The soil pH was measured potentiometric with a digital pH meter in the supernatant suspension of 1:2.5 soils to water ratio [18]. Exchangeable basic (K, Na, Ca and Mg ) ions were extracted using 1M ammonium acetate extraction buffered at pH 7 using mechanical shaking and followed by measuring the concentration in atomic absorption spectrophotometer. Micronutrients were extracted using DTPA extraction and extractant were read with AAS instrument. Total Nitrogen content in shoot part and soil was determined by digesting the samples in sulfuric acid (H 2 SO 4 ) by the Kjeldahl method [19]. Available Phosphorus was determined by Olsen and berry 2 methods using 1 g of air dry soil in 20 ml of 0.5 M NaHCO3 (pH 8.5) shaking for 30 minutes [20] and by shaking 2 g of air dry soil in 20 ml of extracting solution (0.03M NH 4 F and 0.1MHCl) followed by measuring the Phosphorus concentration in the spectrophotometer.

Experimental setup
The type of soil used for all pots was nitisols and 3 kg of soil was filled in plastic pots. Each pot has four holes at the bottom and was equipped with a sealable plastic bag. Each treatment's applied on the plastic pot before planting and mechanically mixed into soil and the treatments were incubated for three weeks at 50% water holding capacity. During the incubation period, the pots were employed in a greenhouse experiment in a randomized complete block design (RCBD). 8 faba bean seeds (cultivar Tumsa) were sowed to a depth of 4 cm in the pots and thinned to 4 plants per pot after seedling emergence. The moisture content of the trial pots was maintained at field capacity by adding water until soil samples were collected after harvest time. For this study ten treatments were used; each treatment was replicated 4 times, giving a total of 40 pots. The treatments were:1) Control soil ; 2) Recommended phosphorus fertilizer only(RPF) as positive control; 3) Coffee husk biochar (10 t h -1 ) + RPF); 4) Coffee husk biochar (20 t h -1 ) + RPF ; 5) Coffee husk biochar (10 t h -1 ) + 50% RPF ; 6) Coffee husk biochar (20 t h -1 ) + 50% RPF; 7) Lime + ISSN 2224-3208 (Paper) ISSN 2225-093X (Online) Vol.11, No.10, 2021 11 RPF; 8) Lime + 50% RPF; 9) 50% lime + biochar 10 t h -1 + RPF ; 10) 50% lime + biochar 10 t h -1 + 50% RPF

Agronomic data collection and measurement
Agronomic data was recorded on a random sample of plants, taken from all four replicates of each treatment. Plant height was recorded from the base of the stem at soil level to the final shoot of the plant of a fully opened leaf on the main shoot and the mean height was expressed in cm. Plant height was recorded at flowering stage of Days after germination. A number of leaves and nodulation No on each tagged plant were counted manually at the flowering stage. Relative leaf chlorophyll content was measured using a chlorophyll meter (SPAD-502). For each chlorophyll measurement, duplicate readings were made on the second fully expanded leaf from the top of the Main plant stem. The dry weight of root and total above ground biomass were measured after 48-72 hrs. The shoot part of the plant Dried in the oven at 70 °C and after these taken for elemental analysis. The initial concentration before planting of micronutrients in the soil such as Fe, Mn, Cu, and Zn are 263.9, 117.69, 4.32 and 1.1 Mg kg -1 soil respectively. The value of macronutrients such as Ca, K, Na, and Mg are 7.28, 2.1, 0.296 and 3.86 Mg kg -1 soil respectively. In biochar sample use as amendment, the values of available K (243 Cmol (+) kg -1 ), P (1109 Mg kg -1 ) is approximately similar with the report of our finding with which is observed by [21]. Ca and Mg and Na value is 16.23, 7.63, and 0.039, respectively.

Effect of biochar on Leaf number, plant height, Root and shoot biomass
The addition of biochar combined with mineral fertilizer in nitisol can improve on the most growth parameters of faba bean as compared to untreated soil. Leaf number, plant height, Chlorophyll content, Nodule number per plant, Root and shoot biomass were significantly higher at (P<0.05) in the application of 20 t h -1 CHB + RPF and 20 t h -1 CHB + 50% RPF than other treatments. The highest values of leaf number and plant height increase by 31 and 12%, as compared to the control and 23% and 9% as compared to mineral fertilizer only respectively and increasing value of shoot and root biomass respectively 2-28% and 2-44% as compared to the control. The observed increase value either due to the addition of biochar in the presence of containing a greater amount of primary nutrient (k and p), due to liming effect to making available P in addition to supplying nutrient to reduced exchangeable acidity (Aluminum toxicity) and some micronutrient to be detrimental to root and plant growth and favorable pH range (> 5.5) for faba bean growth, or (improving chemically, physically and biological properties of soil leads to good soil structure, aeration, porosity, and transportation of available nutrient through the root system. This properties also speed up the microbial reactions and provides micro and macro elements for plant production. These improvements in crop performance are corresponding with other studies [22].

Effect of biochar on Chlorophyll content
Chlorophyll is a light-absorbing pigment (chloroform molecules), and it actually gets its green color since it absorbs blue and red wavelengths of light. The green wavelengths are reflected, giving that particular color to plants and also they related to the N content in green plants and helps as a measure of the response of crops to N fertilizer application and soil nutrient status subsequently deficiency of nitrogen leads to loss green color in the leaves, decrease leaf area and intensity of photosynthesis. Data in Table 2 show that effect of biochar application to soil; significantly change at (p ≤ 0.05) increased the mean values of chlorophyll in a plant grown as compared with the untreated plants.
Similarly, chlorophyll content on the application of lime in acid soil showed significant change but not mineral fertilizer alone is insignificant. In other words; the highest values were recorded in the application of 20 t h -1 CHB and increased by a factor of 27% than control. The increase in leaf chlorophyll content with the plant due to the addition of biochar better to the availability of nutrients and improvement of soil structure such as surface area, porosity, soil reaction, and such properties to makes suitable condition for soil microbial activity. Microbial activity is good decomposer of organic materials that increased N content of faba bean. So this result endorsed in Chlorophyll content, a pointer of photosynthetic activity is related to the N content in green plants and serves as a measure of the response of crops to N fertilizer application and soil nutrient status. The report of this finding is similar with the result which is observed by [23]. Table 2 has shown that all faba bean plants under the different rate of treatments including control showed nodulation may be the inoculation of their seeds with rhizobia, which were responsible for nodulation. The lowest values of nodulation parameters were observed in faba bean under no-biochar application. On the other hand, higher values of nodule number were observed under the treatments of 20 t h -1 CHB + RPF and 20 t h -1 CHB + 50% RPF . Range of nodulation number in plant cultivated in amended soil with biochar was found 6% to 57% increase compared to control. Addition of lime combines with mineral fertilizer also shows significant value on nodulation number of faba bean.

Effect of biochar on nodulation number
The positive effect of the application of biochar due to the result of promoting the efficiency of inoculants or native microorganisms, and increasing soil pH also enhanced mediated microorganisms. The report of this finding is similar with the result which is observed by [24,24], possibly through the release of its labile organic matter, which may have caused immobilization of N [25].

Effect of Biochar on Nutrient (N, P, and K) Uptakes of Faba Bean
Results of the shoot part of analyses for their N, P and K contents (%) have listed in Table 3. From the table the application of the different amount of biochar amendments on the nutrient uptake of N, P, and K is a significantly at (p ≤ 0.05) positive effect as compared to control. These indicate that the application of different treatment supported nutrient uptake of faba bean in the soil solution .N, P, K is the primary nutrient for plant. Most agricultural plants primarily take up inorganic N, P, K which comes from the conversion of organic form to inorganic form (mineralization), although a few crop species like faba bean were observed to directly take up organic N for energy and growth. 3.58 4.85 1.01 LSD; least significant difference; CV the coefficient of variation. Within columns, means followed by the same letter are not significantly different at P = 0.05.
Both 20 t h -1 CHB + RPF and 20 t h -1 CHB + 50% RPF were showed highest value of %N content than with the other treatments but does not showed a statistically significant difference between them. Generally the application of biochar and lime showed a statistically significant difference on the value of %N content compared to control. The lowest value of N uptake obtained from the control (1.43) and highest value 3.28 at the rate of 20 t h -1 biochar. The positive effect of this result indicated due to the addition of biochar to improve soil nutrient solubility, availability, porosity, surface area, soil reaction, water uptake and transportation by the plants through root systems. Since acid soil toxicity of Al 3+ is one of the major limiting factors for crop production by inhibiting root cell division and elongation, reducing water and nutrient uptake. The functions of Biochar not only provide nutrients but also improve physical, chemical and biological aspects of soil fertility and crated optimum condition for active microorganism. The report of this finding is similar with the result which was observed by [1,2,25,26]. Since the solubility of a complex form of iron and aluminum phosphate in soil solution and , due to microbial activity conversation of organic N to the inorganic form of No 3 --N and NH4 + -N increase with soil pH. In acidic soil solubility of Al increase can be toxic to rhizobia and plant roots, limiting legume production of N.
Similar result is observed on P-uptake of faba bean as compared to the control experiment (Table 3). This might be due to increased soil pH as a result of lime application of biochar, which enhances the release of phosphate ions fixed by Al and Fe ions into the soil solution in addition to its Capacity to supply soil nutrients and increased the absorption of P by faba bean compared to the control. Similarly, application of lime together with full and half recommended mineral fertilizer (p) increased P-uptake of faba bean treated with the respective levels as compared to control. Table (3) shown positive increment indicated due to the acid neutralizing capacity of lime. Related to Nuptake, the highest P-uptake 0.16%, 0.15% was obtained from the application of Biochar at the rate of treatment 20 t h -1 CHB + RPF and 20 t h -1 CHB + 50% RPF respectively, while, the lowest (0.084%) was obtained from the control (Table 3). Phosphorus content of the shoot biomass recorded from 20 t h -1 CHB + RPF and 20 t h -1 CHB + 50% RPF greater by a factor of 48 and 44 respectively that of the control. These result indicated both treatments between the combination of biochar and lime with mineral fertilizer and mineral fertilizer alone are 14 shown P uptake of faba bean due to direct transport of available phosphors through root system from it. Like to the % content of N available K was shown a significant change in the application of the rate of biochar and lime at (P < 0.05) compared to control and mineral fertilizer alone. The increment of the result due to the addition of biochar supply K nutrient to plant root and may be due to the rise of soil pH, Plant macronutrient dependent on soil pH. Similar explanations were reported by [2,21,29]  Our results indicated enhance of soil exchangeable base such as K, Ca and Mg but the application of biochar in soil was not a significantly positive effect on the property of soil exchangeable Na + . The treatment of biochar in soil, exchangeable K more improves when compared to the other three elements. The application rate of biochar increase with increased availability of soil exchangeable K. Addition of 20 t h -1 CHB the highest value of exchangeable K + compare to inorganic fertilizer (P) alone and control and increased by a factor of 82% and 85% respectively. In other word, addition of mineral fertilizer for each treatment is not shown a statistically significant difference on the property of soil available nutrient. However, acid soil amended with lime positively influenced on the nutrient availability of soil. These increment of nutrient availability may be due to the liming effect of the addition of biochar and lime to retained nutrients (reduced leaching of nutrient) and also due to the presence of a maximum amount of available K in the biochar to release into the soil system due to decomposition and mineralization. The report of this finding is similar with the result which is observed by [29,30]. Coffee husk compost contains high organic agricultural waste and potassium was good material for composting process in agricultural products further designate by [31,32]. Our findings indicate that the effect of biochar on soil micronutrient was significantly reduced at (P ≤ 0.05). micronutrient are trace elements used for plant as nutrient but may also pose a toxicity risk if present at elevated levels as their availability and mobility increases under acidic condition. Application of 20 t h -1 CHB reduced the Concentration of iron by 32% and manganese by 25% as compared to the control. This observation may be due to the liming effect of biochar addition immobilized the micronutrient in soil by precipitation which reduces the concentration of Fe, Cu, Mn, and Zn. From the above discussion of exchangeable acidity reduced due to the addition of biochar and increased soil p H , as soil p H increase rise availability (solubility) of macronutrient and formation of complexes with micronutrient increased. Our finding associated with [30] reported that the application of coffee waste increased soil pH due to its liming effect. This brought about an increase in cation exchange capacity with a substantial reduction in phytotoxic Al and decrease in the availability of a number of metals (Cu, Zn, Mn, and Fe) and significantly reduced their uptake by ryegrass.

CONCLUSIONS
Initially the study soil was showed that deficient in plant-available nutrients and application of the biochar and lime significantly positive effect on soil nutrients in addition to nutrient supply, by increasing soil pH and reduced exchangeable acidity, in a way that enhanced the availability of plant nutrients. Applications of 20 t h -1 CHB were more efficient in improving soil nutrient availability, and nutrient uptake of faba bean than other treatment. The relatively high alkalinity and probably the proton consuming ability of ash materials, as well as the high nutrient contents in biochar, were considered the main factors responsible for the reduced soil acidity and improved nutrient supply of the amended soils. Generally, all the result of soil and plant nutrient obtained with the acceptable analytical methods which were evaluated by analytical method validation and quality control parameters such as precision accuracy, reliability by measurements of replication, method blank, spike recovery was taken.
The positive growth response of the faba bean to biochar and lime soil amendments than control indicated that the soil collected for this research was inherently low in some essential nutrients, hence the level of many essential nutrients in these soils was fixed and lower which was readily available and supplied by biochar and lime amendments. The faba bean was more responsive to the organic source (biochar) amendments compared to the lime, thus indicating there were some important nutrients that were being supplied to the faba bean beside its liming effect. While lime was not used as nutrient sources other than reducing the Aluminum toxicity effect and making the nutrients available for the growth. Liming acid soils result in the release of fixed macronutrients specially phosphorus for plant uptake by decreasing Al. Therefore this is particular importance as it indicates the value of biochar as alternative amendments to ameliorate soil nutrient and acid soils for small-scale farmers who cannot afford to regularly purchase lime and mineral fertilizers.