Effect of Biochar Application on Growth of Garden Pea ( Pisum sativum L . ) in Acidic Soils of Bule Woreda Gedeo Zone Southern Ethiopia

The aim of this experiment was to study the effect of types and rates of biochar on growth, yield, and yield component of garden pea at Bule wereda, Southern Ethiopia. The treatments consist of two types of biochar (corncobs and Lantana camara) and four rates of biochar (0, 6, 12, and 18 t ha). The experiment was laid out as a randomized complete block design in a factorial arrangement with three replications. Soil samples were collected at a depth of 0–30 cm and germination parameter and phonology of garden pea were recorded. The result showed that soil bulk density, porosity, pH, and exchangeable acidity were significantly (P < 0.001) affected by biochar application. The result also showed that maximum germination percentage of garden pea seeds (95.23%) was recorded at 18 t ha of Lantana biochar. The shoot length was significantly (P < 0.05) affected at 15 days and 30 days of biochar application. Moreover, fresh shoot weight and dry root biomass, number of seeds per pod, and grain yield of garden pea were significantly affected (P < 0.05). Of the substrate and application rate applied, Lantana camara 12 t ha and Lantana camara 18 t ha significantly increased yield of garden pea. Thus, further studies on effect of different biochars and their specific role are suggested to increase crop production.


Introduction
1.1.Background of the Study.Soil acidity reduces 30-40% of world's arable land crop production [1].There are several estimates of the extent of acid soils and its impacts on crop production in the world.According to [2] acidic soils cover 1,455 million ha or about 11% of the total global land surface.Other scholars such as [3] had higher estimates and reported that acid soils covered 3,950 million ha or 30% of global arable land.
In Ethiopia 40.9% of the soil is acidic; out of which 27.7% is moderately to weakly acidic (pH of 5.5-6.7) and 13.2% is strongly to moderately acidic (pH < 5.5) [4].A secondary data obtained from Gedeo zone agricultural office indicates that Bule wereda was soil strongly affected by soil acidity.The soil pH of the study area is less than 5.5.This indicates that Bule wereda soil pH is categorized under strongly acidic soils [5].
Low crop productivity in many regions of the world is mainly caused by low soil pH and high aluminum content [6].The soil amendments widely used to increase soil pH include dolomite, calcite, and lime and which in turn reduce exchangeable aluminum, iron, and hydronium in the soil [7][8][9].Application of lime not only increases the soil pH, base saturation, exchangeable calcium, and magnesium but also increases crop yield [1,10].However, limestone material is relatively expensive and challenging to afford for the subsistence farmers and the supply is limited supply in Ethiopia [11][12][13].Due to this, farmers have recently started using biochar and organic matter as an alternative soil amendment mechanism and increase crop yield as these materials are locally available and cheaper compared to limestone [12,14].
The use of biochar for soil improvement for crop yields in agricultural fields is lately recognized [15].Biochar is carbon rich product obtained from different feedstock at low temperatures (<700 ∘ C) [16].It stores carbon for long time to improve soil fertility and optimized soil pH [17].Application biochar not only increases crop productivity and soil cation exchange capacity (CEC) but also is possible to increase soil macro-and microelement [18][19][20].Biochar is made from different feedstock such as wood chip and wood pellets, tree bark, crop residues, and organic wastes [14].Different studies reported that biochar increases soil pH, plant growth, and yield [6,21] but few studies reported the influence of biochar on early stages of plant growth such as on seed germination and seedling growth in different regions of the world [8].
In Ethiopia most studies have focused on effect of biochar on soil physical and chemical properties and have not investigated the impact on seed germination or root growth [6,22].Therefore this study was initiated (1) to evaluate the effects of Lantana camara and corncob biochar on yield and yield component of garden pea at Bule acidic soils and (2) to explore the effects of biochar on growth performance of garden pea.

Description of Study Area.
The experiment was carried out at Bule woreda, Gedeo Zone, Southern Ethiopia (Figure 1).The area lies between 6 ∘ 04  16  and 6 ∘ 23  50  N latitude and from 38 ∘ 16  20  to 38 ∘ 26  11  E longitude at an altitude ranging from 1700 to 3000 meter above sea level [23].The mean annual rainfall ranges from 1200 mm to 1800 mm.The area is characterized by a bimodal rainfall distribution (Figure 2).The mean annual temperature is 10.6 ∘ C and lies in the cold thermal zone of Ethiopia [24] indicating that only cold growing crops can be cultivated in the area.The area is also categorized as moist dega zone as per traditional system.The soils of the experimental site are mainly nitisol [25].The land-use system of the study area is a mixture of crop farming and agroforestry system [24].Thus, 85% (21, 890 ha) of the land is used for growing annual and perennial crops while 497 ha are used for grazing, 1,904 ha  [15].After pyrolysis process, the biochar was grounded to small granules and passed through 2 mm sieve in order to have the same particle size as that of soil.

Experimental Treatments and Design.
The experiments consist of two types of biochar (corncob and Lantana camara) and four rates (0, 6, 12, and 18 t ha −1 ).The experiment was laid out as a randomized complete block design in a factorial arrangement with three replications.A total of 24 plots each measuring 2 m × 2 m (4 m 2 ) were used for the experiment.Plots were separated by 0.5 m and each replicate was by 1 m apart to avoid edge effect.The description of treatment is shown in Table 1.

Experimental Procedures.
Treatments were incorporated into the plots manually and left for 60 days.Priming of seed 24 hours before sowing was done to regulate the germination process.Plant to plant spacing is maintained 5 cm and row to row spacing is maintained 20 cm and planting depth was 1 cm.There were 9 rows in each plot and 14 plants in each row and a total of 126 plants per plot.Weeding was done manually at two weeks interval till harvest.The recommended fertilizer 2 kg NPS (each 0.6 kg) were applied during planting and the tested crop was raised under rain feed system.
2.5.Soil Sampling.Initial soil samples were collected randomly from twenty-four observational points on the site at the depth of 0-30 cm before the experiment.The soil samples were thoroughly mixed to form a composite soil sample and used for the determination of the soil physical and chemical properties.Also, core soil sampler of 167 cm 3 was collected from 36 plots at the depth of 6 cm in each plot at 90 days and used for the determination of soil bulk density.
2.6.Soil Laboratory Analysis.Soil texture was determined by the hydrometer method.Bulk density was determined using the core method [26] in which a stainless steel core (5 cm in diameter and 10 cm in height) was used to collect soil core to determine soil bulk density (Bd) in each sampling time during incubation.Total porosity (Tp) is calculated from bulk density using the formula Tp = 100(1 − Bd/Pd), where Bd is bulk density, Pd is particles density, and Pd is assumed to be 2.65 g cm −3 [27].Soil organic carbon was determined by the Walkley-Black oxidation method [28].Total nitrogen was measured by the Kjeldahl method [27] and soil pH (H 2 O) by a pH meter with soil to water ratio of 1 : 2.5 [29].
Available phosphorus was determined by Bray-1 method, while potassium was measured with the flame photometry method [31].

Germination Parameter Study
Germination.Germination percentage of seed from each treatment was calculated on the basis hypocotyls appeared above the surface of soil.
Percentage of seed germination (%) =   * 100, where  is percentage of seeds germinated between two consecutive counts,  is time taken since germination experiment started, and  is total percent of seeds germinated.
Germination Index.The numbers of germinated seeds were counted daily until the completion of experiment.Germination index (GI) was calculated using the following formula recommended by Khandakar and Bradbear (1983): where  1 ,   root length.The shoot and root length were measured in fresh using a ruler from the point near to soil surface to the longest portion of the plant tip at maturity and then average was calculated [32].The parameters such as number of pods/plants, number of seeds/pods, fresh weight of shoot and roots, and dry biomass of shoot and root and the grain yields (kg/ha) were assessed [32].
2.9.Data Analysis.The data collected were subjected to descriptive statistics to calculate germination percentage, mean germination time, and germination index by using Ms-Excel spreadsheet version 2010.SAS version 9.1.3was employed to determine analysis of variance (ANOVA) different phonological data of garden pea and the mean values were compared with least significant difference (LSD) at  value 0.05.[33] for Ethiopian soils and tropical soils.The pH of the soil was 4.7 showing very strongly acidic nature of the soil [24], bulk density (0.82 g/cm 3 ), particle size (51%), sand (36%), silt (13%), and clay and textural class is sandy loam.The textural class of the experimental site was sandy loam.

Effect of Biochar on Soil Physical and Chemical Properties.
Soil bulk density, porosity, pH, and exchangeable acidity were significantly ( < 0.001) affected after the application of biochar Table 2.This is due to the presence of ash in the biochar that decreases in bulk density and exchangeable acidity and increases soil pH and soil porosity of the biochar amended soil [34].These findings are in agreement with the recent research work by [11] who reported a decrease in soil bulk density and exchangeable acidity and increases in soil porosity and soil pH after biochar application, whereas total nitrogen, soil organic carbon, available phosphorus, and potassium are not significantly affected after application of (Table 2).This is attributed to the large carbon, nitrogen, and potassium component of inside the biochar [35].Similarly [36] reported that significant increase of soil potassium, carbon and nitrogen, potassium, and available phosphorus was recorded by the application of biochar.

Effect of Biochars on Germination of Garden Pea Seed.
The germination percentages (GP) range from 77 to 96.02% in different treatments but the statistical analysis revealed that it is not statistically significant differences (Figure 3).Similarly, other parameters such as mean germination time (MGT) and germination index (GI) were also affected by different rate of biochar as compared to the control.Biochar application did not decrease germination.The maximum germination percentage (GP), mean germination time (MGT), and germination index (GI) were (96.02% and 24.03%) at rate of 18 t ha −1 of Lantana biochar application, respectively.This is due to the fact that biochar had a certain degree of adsorption and contains a certain amounts of minerals elements of soils which may provide nutrients for seed germination.Similarly [32] reported that biochar sorptive capacity for allelochemicals may increase in plant germination.This study was in agreement with [37] who reported that biochar application has been increase germination parameter of pea seeds.

Plant Height.
Plant heights were influenced by biochar 15 and 30 days after planting.However, these differences disappeared by 15 days (Table 3).This could be due to the slow release of nutrients/to neutralize the acidic soil.The application of 12 t ha −1 of Lantana camara biochar significantly increased plant height as compared to other treatments in contrast to [36] where it was reported that biochar did not influence plant height.

Root Biomass.
Both fresh and dry root biomasses were significantly affected by application of different rate of biochars ( < 0.005).Application of Lantana biochar at 6 t ha −1 and 18 t ha −1 significantly increased (4.9 and 4.7 kg, resp.)fresh root biomass whereas application of Lantana biochar 6 t ha −1 increased (3.10 kg) the dry biomass as compared to other treatments (Table 4).One of the reasons for root biomass increased in this study was that the biochar of Lantana greatly improves the soil acidity and enhances root growth.

Pod Number per Plant.
Pod number per plant was also significantly affected by different rate of biochar.The results indicated that the highest pod numbers (28.67 kg) were recorded under the application of Lantana biochar at the rate of 12 t ha −1 (Table 5).This might be due to the fact that soil amelioration and crops supplied with adequate nutrients have more vegetative growth, longer linear growth rate, and more dry matter accumulation which is directly related to an increment in pod number.This result is in agreement with that of [32] who reported enhancement of pod number of pea in response to applying of rice husk biochar, while wood biochar has its less effect than all other biochar applications.

Seed Number per Pod.
Seed number per pod at physiological maturity was significantly affected by different rate of biochar ( < 0.005).The higher number of seeds was recorded under Lantana biochar at the rate of 6 t ha −1 as compared to other treatments (Table 5).This implies that as the number of productive seeds per pod increases the yield per hectare also increases.The increase may be associated with increase in the number of seeds per plant, sustained nutrient supply, increased photosynthetic activity [38], and good translocation efficiency [39].Similar to the present study, high seed numbers per pod were reported for soybean sown in low pH soil that was amended with biochar [32].According to [36] number of seeds/pods of pea was highly significantly affected by application of biochar of different origin.
3.8.Shoot Biomass.Shoot fresh and dry biomass yield was enhanced by application of Lantana biochar 6 t ha −1 and Lantana biochar 18 t ha −1 , respectively (Table 5).One of the reasons for shoot biomass yield increase in this study was the production of more vigor growth in the higher rates of Lantana biochar.Similar to the current study, [12] reported that the highest shoot biomass yield was obtained under plants supplied with high rate of biochar.
3.9.Gain Yield.Grain yield was significantly affected by different rate of biochar ( < 0.05).Application of Lantana biochar at increased rates from 12-18 t ha −1 significantly increased grain yield compared to the rest of the treatments (Table 4).Significantly lower (134.17kg/ha) grain yield was recorded under unfertilized corn control and corn biochar at the rate of 6 ton/ha.Application of Lantana biochar significantly increased grain yield over the corn biochar and control treatments (Table 5).This could be attributed to reclaim in the level of soil acidity from application of biochar and in turn increases the number of pods and seeds per plant and hence grain yield.
Similarly, [30,40] noted significant increase in grain yield of teff with increasing rates of biochar.[41] also reported that application of biochar on maize grain yield had significant effect in subsequent years and maize yield increased with increasing biochar rate.

Conclusion
This study indicates that different physical properties of the soil such as bulk density, total porosity, and the chemical properties such as total nitrogen, available phosphorus, potassium, and pH and soil organic carbon of the soil were improved due to application of biochar compared to the control.The increased soil pH and soil porosity and decreasing bulk density and exchangeable acidity value may be due to the ash content in biochar.Similarly increasing soil pH and a reduction of exchangeable acidity were observed from the experiment.Due to the application of biochar germination percentage, mean germination time, and germination index, plant height, fresh and dry weight of shoot and roots, number of pods/plants, number of seeds/pods, and yield of it were significantly increased.Of the two feedstocks, Lantana biochar was found to have greatest effect in pea seedling growth compared to corncob biochar.Among the biochar from different feedstock, Lantana camara biochar was found to be effective in increasing agronomic parameter in comparison to other corncobs biochars.Farmers in Bule mostly practice to use liming in acidic soil, which is a shortterm increase in nutrient availability with not any longterm effect on the soil health.This practice could be easily replaced by the formation and application of biochar.This could produce the long-term beneficial effect on the soil health together with the increased yield.

Figure 3 :
Figure 3: Effect of biochar on garden pea germination parameter.

Table 1 :
Treatment used in experimentation.
2 ,  3 , . . .,   , are proportions of seed which germinate on days 1, 2, 3, . . .,  following setup of the experiment.If seeds sown were germinated at the same time equally, we considered all are germinated 100% while if none of the seeds are germinated all in all we considered the germination index is 0%.
2.8.Phonological Observation of Garden Pea.Ten sample plants from each plot were selected randomly to determine various phenological characters such as shoot length and

Table 3 :
Mean fifteen days, twenty days, twenty-five days, and thirty days of pea as influenced by different rate of biochar at Bule.

Table 4 :
Mean root length, root fresh weight, and root dry biomass of pea as influenced by different rate of biochar at Bule.

Table 5 :
Effect of different biochar on shoot fresh weight, shoot dry biomass, pod number, seed per pod, and grain yield of pea as influenced by different rate of biochar at Bule. = shoot fresh weight, SDB = shoot dry biomass, PN = pod number per plant, SP = seed number per pod, and GY = grain yield.Means with same letters are not significantly different from each other at 5% probability level. SFW