Soil Test Based Fertilizer Calibration for Common Bean ( Phaseolus vulgaris L. ) Varieties of the Southern Ethiopia

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Introduction
Low crop production is inappropriate soil fertility management [1]. Te relatively low yield of common beans in Ethiopia including the study area is as a result of the low use of enhanced variety and low soil fertility status and poor management practice which are the major production constraints [2]; ATA [3]. Wossen [4] reported NPKSB nutrient ratios for common bean growth and yield. However, soil fertility mapping projects in Ethiopia recently reported the defciency of K, S, Zn, B, and Cu in addition to N and P in major Ethiopian soils, and thus recommend the application of customized and balanced fertilizers [5]. Common bean N fertilizer requirement depends on soil fertility levels; for low soil nitrogen levels (below 34 kg N·ha −1 ) N fertilizer is generally recommended in order for defciency symptoms not to manifest and for full development up to production, inorganic phosphorus fertilizer has a positive efect on the yield and yield components of common bean and sulfur is required in similar amount as that of phosphorus [6]. In Ethiopian soils, the defciency of K, S, Zn, B, and Cu in addition to N and P have common bean recently reported by soil fertility mapping project, and thus recommend the application of customized and balanced fertilizers [11]. Te fertilizer recommendation did not consider the existing soil nutrient supply and resulted in low crop yield response in the region [2]. To correct these nutrient defciencies, farmers in the Gurage zone of the Southern Ethiopia have been using a uniform blanket application of 100 kg NPSB ha −1 for all legumes including common bean to increase crop yields and this did not consider soil fertility status and crop requirement. Terefore, this study was initiated with the following objectives to determine the efect of blended fertilizer on growth, yield, and yield components and on nutrient uptake and nutrient use efciency of common bean varieties and to identify and suggest the economically feasible rates of NPSB fertilizer for common bean varieties production in the study area.

Description of the Study Site.
Te experiment was conducted at Dobo Tuto Kebele, Meskan District, Gurage Zone, Southern Ethiopia, during the 2020 rain season. It is located 135 km south of Addis Ababa at a latitude and longitude range of 7°.99′35″-8°.02′781″N and 38°.26′31′-38°.57′86″E, respectively ( Figure 1). Te area has an elevation range of 1823-2000 meters above sea level. Te mean annual rainfall is 1000-1200 mm with a bimodal pattern, which extends from February to April and June to September. Te mean annual minimum and maximum temperatures are 10.3°C and 26°C, respectively ( Figure 2).

Experiment Design and Treatments.
Te treatments were consisted of a factorial combination of six blended NPSB fertilizer rates (0, 50, 100, 150, 200, and 250 NPSB kg ha −1 ), and two varieties (awassa dume and Nasir) were evaluated in a factorial arrangement laid in a randomized complete block design with three replications. Each plot size was 2.4 × 3 m 2 , which contained six rows per plot and the four central rows were used for data collection, the spacing between rows and plants were 40 cm and 10 cm, respectively. Blended NPSB (19% N, 38% P 2 O 5 , 7% S, and 0.1% B) was used as sources of N, P, S, and B, respectively, for the study.

Soil-Plant Samples and Analysis.
Before planting, soil samples were taken randomly in a zigzag manner to a depth of 0-30 cm from 20 spots of the experimental feld (Table 1). Te soil samples were composited to one sample and airdried ground and sieved using 2 mm and 0.5 mm (for organic carbon). Ten, the composite soil sample was analyzed for soil pH in water and was determined potentiometrically in a supernatant suspension of 1 : 2.5 soils: water ratio using a combined glass electrode pH meter [14]. Soil texture was determined by the Bouyoucos hydrometer method [15]. Soil organic carbon (SOC) was using the Walkley and Black method [16], total nitrogen (TN) was using the Kjeldahl method [17] available phosphorous (AP) was using the Olsen method [13], cation exchange capacity (CEC) was extracted by 1M ammonium acetate (pH 7) method [18], available sulfur (AS) was determined using the turbid metric method, and available boron (AB) was determined using the hot water method [19]. After harvesting the plant samples was collected, dried, processed, and analyzed for total N, P, S, and B contents were determined by wet acid digestion procedure as suggested [20].

Data Collection
An efect of blended NPSB rate was examined by measuring data on phenology, growth, yield, and yield component parameters.

Efciency Parameters.
Te actual uptakes of N, P, S, and B based on the potential supplies of N, P, S, and B were calculated using equations (1)-(4) as described in [21] as follows: where PE is thephysiological efciency, BY f is the biological yield (grain plus straw) of the fertilized pot (kg), BY u is the biological yield of the unfertilized plot (kg), N f is the nutrient uptake (grain plus straw) of the fertilized plot, and N u is the N uptake of the unfertilized plot (kg).
where RE is the recovery fraction, TU a -average total nutrient uptake, kg ha −1 from treatments receiving a dose Fr (a) TU a0 -average total nutrient uptake, kg ha −1 , from the control treatments, F ra is the rate of fertilizer application (kg ha −1 ), and (a)-nutrient under consideration, namely, N, P, or K. where AE is the agronomic recovery, kg kg −1 ; G f is the grain yield of the fertilized plot, kg; G u is the grain yield of the control plot, kg; and N f is the quantity of N, P, and K fertilizer applied, kg. Where EU: Utilization efciency, Nutrient utilization efciency is the product of physiological and apparent recovery efciency. It can be calculated as follows:

Efciency of Soil Nutrient Was Calculated from Soil Test
Value. Calculation of the important parameters (NR, Cs, and Cf ) was computed following the formula as defned by [22] as follows:

Percent contribution of available Nutrient from soil(%Cs) �
Total uptake of nutrient in control plot Soil test value of that nutrient in control plot x 100,

Fertilizer Requirement Equations
where (% Cf ) is the percent contribution of nutrient from fertilizer, FN is the fertilizer nitrogen (kg N ha −1 ), FP 2 O 5 is the fertilizer phosphorus (kg P 2 O 5 ·ha −1 ), FS is the fertilizer sulfur, and FB is the fertilizer boron. T is the targeted yield (q ha −1 ), SN is the soil test value for available nitrogen (kg ha −1 ), SP is the soil test value for available phosphorus (kg ha −1 ), SS is the soil test value for available sulfur (kg ha −1 ), and SB is the soil test value for available boron (kg ha −1 ).

Economic Analysis.
Economic analysis was performed using partial budget analysis following the procedure of CIMMYT [28].

Statistical Analysis.
Agronomic data were subjected to analysis of variance (ANOVA) using SAS 9.0 version software [29]. Least signifcant diferences (LSDs) were used for mean separation comparison at a probability 5%.

Efect of Blended Fertilizer on Yield and Yield Components of Common
Bean. Te analysis of variance indicated that the main efect of varieties and NPSB rates had a highly signifcant efect (p < 0.05) on plant height (Table 2). Te tallest plant height (97.96 cm) with the application of 100 kg·ha −1 NPSB rate, whereas the shortest plant height (79.6 cm) was recorded from 0 kg·ha −1 NPSB rate for the same variety (Table 2). Te highest number of nodules per plant (39.2) and nodule dry weight (0.76 g) were recorded from variety awassa dume with application of 100 kg·ha −1 NPSB blended fertilizer, whereas the lowest nodules number (21) and nodule dry weight (0.20) were recorded from 0 kg·ha −1 by variety Nasir (Table 2). Te highest number of primary branch per plant (4.6) was recorded for the Nasir variety with a blended fertilizer treatment (NPSB) of 100 kg·ha −1 , while the minimum number of primary branch per plant (2.8) was from the awassa variety Dume (Table 2). Te highest number of pods per plant (52.04) was obtained from the application of 100 kg·ha −1 blended NPSB fertilizer rate from Nasir, whereas the minimum number of pods per plant (39.65) was recorded from 0 kg ha· −1 NPSB fertilizer rates gave from awassa dume ( Table 2). Tese results were consistent with the fnding of Haleh et al. [30], Lake and Jemaludin [31] and, Turuko and Mohammed [28] reported yield and yield components statistically infuenced by the application of NPSB application. Te analysis of variance showed that the main efect of varieties and blended NPSB fertilizer rate had shown a highly signifcant (p ≤ 0.01) efect at the same time the interaction of fertilizer application and varieties also had showed signifcant (p < 0.01) efect on the above ground dry biomass. Te highest above ground dry biomass yield (5358 kg·ha −1 ) gave at a fertilizer rate of 100 kg·ha −1 NPSB with variety awassa dume, whereas the lowest dry biomass yield (3918 kg·ha −1 ) was obtained from control with variety Nasir (Figures 3(a)-3(c)). Te highest hundred seed weight (28) was recorded from the variety awassa dume, while the minimum seed weight (21) gave with control from the Nasir variety (Figures 4(a)-4(c)). Te highest harvest index (36.2) with an application rate of 100 kg·ha −1 blended fertilizer, whereas the lowest record (24.06) was registered from 0 kg·ha −1 NPSB rate for the same variety (Tables 3-5). According to Girma [29] who found a signifcant increment in the biological yield of common bean with an increased rate of NP fertilizers from 0 kg P 2 0 5 ·ha −1 and 69 kg P 2 0 5 ·ha −1 (150 kg DAP) and Tesfaye [30] reported that 100 seed weight in common bean increased with increase in phosphorus fertilizer application (69 kg·ha −1 ).

Nutrient Use Efciency.
Variation in agronomic use efciency appeared to result from diferences between varieties and levels of NPSB fertilizer. Among NPSB application, the Nasir variety interacted with 100 kg·ha −1 NPSB level being observed with the greatest agronomic efciency which reached 7.43 kg·kg −1 whereas, the awassa dume variety interacted with 250 kg·ha −1 NPSB level was low agronomic efciency which reached 1.84 kg·kg −1 . As results indicated in (Table 6), the highest nutrient recovery efciency (38.2%) was revealed with Nasir variety by fertilizer rate 100 kg·ha −1 , and the lowest nutrient recovery efciency (3.67%) and (4.15%) was found from a fertilizer rate 250 kg·ha −1 with awassa dume and Nasir varieties, respectively (Figures 3(a)-3

(d) and 4(a)-4(d)).
Te highest physiological nutrient use efciency (6.74 kg·kg −1 ) was recorded from the Nasir variety by a fertilizer rate of 100 kg·ha −1 . Since overhead fndings, it was manifested that higher application of nutrient has resulted in more nutrient uptake (Figures 4(a)-4(d)). In line with this result, Malakouti [31] reported that the NPK fertilizer can increase fertilizer use efciency and grain yield for diferent crops. Likewise, Jones et al. [32] stated that macronutrients and micronutrients of the grain yields of common bean were also increased [31].

Validation of the Fertilizer Requirement Equation.
A confrmation study was leaded on the farmers' feld for one year to verify the routine of the equation. In the confrmation study, six treatments including the soil-test based of NPSB rates, 98% of the soil test-based P rate, 93% of the soil test-based S rate, 61% of the soil test-based B, and NPSB recommendations (100 kg NPSB kg ha −1 ) were evaluated on the grain yield of common bean verities. Te data for calculating the fertilizer dose for the target yields of the awassa dume and Nasir varieties are shown in Tables 4 and 5. Te application of NPSB blend fertilizer has a benefcial result of improving soil fertility and higher fertilizer use efciency at 250 kg·ha −1 in both cases. For soil fertility management, it is necessary to select appropriate yield targets and apply fertilizers that produce the highest yields of awassa dume (2312 kg·ha −1 ) and Nasir (2995 kg·ha −1 ) at 100 kg NPSB ha −1 . Consistent with Tedesse and Dechassa [33] reported that the nutrient requirements of the common bean are high yielding.   Applied and Environmental Soil Science 4.4. Partial Budget Analysis. Te result of the data showed that the maximum and minimum gross beneft was obtained 70065 and 47736 ETB (Ethiopia Birr ha −1 ) from a fertilizer rates 100 kg·ha −1 and 0 kg·ha −1 from Nassir and Hawssa Dume varieties, respectively. Te highest net beneft 67665 ETB was recorded from a treatment treated by a fertilizer rate of 100 kg·ha −1 with the Nasir variety and the lowest net beneft 47736 ETB was received with a rate of 0 kg·ha −1 from the awassa dume variety. At the same time, the maximum rate of return (8.66%) was obtained with a fertilizer rate of 50 kg·ha −1 in the awassa dume variety (Table 7) and (13.65%) with a fertilizer rate of 100 kg·ha −1 with Nasir variety (Table 8).

Conclusion
Low use of fertilizer and crop nutrient imbalance are the major constraint in realizing the high productivity of all cultivated crops in the study area. Tus, the study was conducted to assess the efect of diferent levels of blended NPSB fertilizer on growth, yield, and yield components, and use efciency of common bean varieties. Treatments consisted of two common bean varieties with six blended NPSB fertilizer rates (0, 50, 100, 150, 200, and 250 kg·ha −1 ) applied in RCBD with three replicates. Te result of the experiment revealed that the interaction of varieties and NPSB fertilization had showed a signifcant (p ≤ 0.01) efect on plant height, nodule number, nodule dry weight, number of primary branches, number of pods per plant, biomass yield, grain yield, and harvest index. Te partial budget analysis indicated that the highest net beneft (67665 ETB ha −1 ) was obtained from variety Nasir with the application of 100 kg·ha −1 NPSB, whereas the lowest was from variety awassa dume (47736 ETB ha −1 ) with no fertilizer application. Tus, it can be inferred that the application of 100 kg·ha −1 NPSB with variety Nasir was found to be higher and can be used for common bean production in the study area. However, the result of the study must be validated and approved in diferent agroecologies to give a comprehensive recommendation for a wide range of common bean production.

Data Availability
Te data used to support the fndings of this study are available from the corresponding author upon request.

Conflicts of Interest
Te authors declare that they have no conficts of interest.