The Response of Haricot Bean (Phaseolus vulgaris L.) Varieties to Phosphorus Levels on Nitosols at Wolaita Zone, Ethiopia

A field experiment was conducted at two locations (Bolosso Sore and Damot Sore) in Wolaita Zone of Southern Nations Nationalities and People’s Regional State (SNNPRS) to evaluate the response of two varieties of haricot bean (Phaseolus vulgaris L.) to phosphorus fertilizer rates on acidic soils. Combinations of four levels of P (0, 10, 20 and 30 kg ha -1 ) were used on two varieties. The treatments were arranged in factorial RCBD with three replications. Analysis result of soil samples showed that OC, Av.P, TN and soil pH values were very low. Application of lime with P results significant changes on these chemical properties of the soils in the two locations. The maximum values of these parameters were recorded at 30 kg Pha -1 . Growth parameters, yield and yield components were significantly increased with increasing rates of P at the two locations (year1&2). Maximum grain yields (1488.40 and 1523.7 kgha -1 for Hawasa Dume at Gununo and Dolla, respectively and 1242.12 and 1352.01 kgha -1 for Omo-95 at Gununo and Dolla, respectively) were recorded at rates of 30 kgPha -1 in both locations. From the result of this study it could be conclude that it can improve soil pH, Av. P and performance of haricot bean varieties but till now there is some gap on correcting P application of grain yield of the varieties. So application of P could be increased the production of the crops.


INTRODUCTION
Haricot bean (Phaseolus vulgaris L.) is annual pulse crop with considerable variation in habit, vegetation characters, flower color and the size, shape of pods and seeds (Onwueme and Sinha, 1999). It was probably first cultivated with maize, and it seems likely that the two crops evolved together in a cereal-Legume farming system in much the same way as cowpeas and sorghum in West Africa. It is widely cultivated throughout different parts of Ethiopia. It is produced in four major agro ecological zones, including the central, eastern, southern and western zones. Haricot bean is mainly used as source of food and cash. It is exported to earn foreign exchange and is also one of the cash crops locally used by farmers as source of food. Additionally farmers also grow the bean to use as forage for livestock and mulching. Haricot bean cultivation can be carried out without large input and intensive practices and this makes it suitable for poor farmers where the need in food supply is important. It can be used in intercropping system with maize and between young trees until canopy closure.
Yield of legumes in farmers' field is usually less than 0.65t/ha against the potential yield of 1.2t/ha suggesting a large yield gap (CACC, 2002). Low yield potential of legumes has made them less competitive with cereals and other high value crops. The yield of haricot bean increase with p application and its nodulation and fixation of N can also be improved with the application of P (Gemetchu, 1990). The average national productivity of haricot bean is 0.72t/ha (CACC, 2002) and its regional productivity is 0.81t/ha.
The major bean producing area in the southern zone includes Gamo Goffa, Sidamo and Wolaita (Gemetchu, 1990). Haricot bean is also one of the most communal cultivated pulse crops in the Wolaita area where its yield is lower than regional and national yields. The low yield is contributed from acidity of soils which reduce availability of P and basic cations as Ca and Mg and also affect activities of soil microorganisms (Havlin et al., 1999).
Besides, the farmers also grow the bean to use the straw as forage for livestock, source of fuel, mulching, bedding, and covering material for houses of poor farmers. Despite all these advantages, little effort was made to improve its productivity and the yield is comparatively low because of depletion of nutrients as a result of erosion and crop mining, lack of optimum fertilizer rate, etc. One of the solutions to alleviate the problem could be applying P fertilizers from external sources based on recommended rate for the crop . In order to make site -specific recommendation of P for haricot bean production, characterization of the soil at the experimental site, and nutrient rate experiment are needed. Therefore, this study was initiated with the objectives to characterize the soil of the experimental site, and evaluate the response of haricot bean to increasing levels of P application.
Even though application of lime with P brings positive effect on soil conditions and crop performance, in Wolaita area where the problem of soil acidity is very chronic, little or no work is done to verify whether there is response of crops to P application rates with liming or not. Furthermore, to use fertilizer with lime as source of nutrients, there should be site-specific recommendation to maintain optimum level of nutrients. Therefore, this study was initiated with the following objectives.
To evaluate the response of haricot bean varieties to different rates of P fertilizer To compare the performance of haricot bean varieties To observe the interaction effect of P with haricot bean varieties

Description of the Study Site
The researches were conducted during the 2012-2013 rainy season at two locations, which is located in Wolaita Zone, Southern Nations Nationalities and People's Regional State (SNNPRS). The first one was at Boloso Sore district, which is located at 307 km south of Addis Ababa and 5 km from Areka town, at 7°04.196 ' N and 37°41.330' E and altitude of 1790 meters above sea level.
The second location was Damot sore district, which is located 330 km south of Addis Ababa and 2 km from Gununo town, at 6°56' ' N and 37°.39' E and altitude of 1790 meters above sea level. There was no meteorological station in the study area, which is found 3km far from Boloso Sore district. The two districts are with mean annual rainfalls of 1460 mm with a bimodal pattern, which extends from March to September. The peak rainy months are April, July, August and September. The mean minimum and maximum temperatures are 15 o C and 26 °C, respectively. The representative date was collected from Areka Agricultural Research Center.

Treatments and Experimental Design
Hawassa Dume and Omo-95 haricot bean varieties were used for test crop to compare its response to phosphorus fertilizer rates. The levels used were 0, 10, 20 and 30 kg P ha -1 . The treatments were arranged in factorial RCBD with three replications. Five rows each with fifteen plants were used on plot having size of 2.0 m by 1.5 m. Spacing of 10, 40, 50 and 100 cm were used between plants, rows, plots and blocks, respectively. Urea at rate of 50 kg ha -1 and all doses of P were applied at planting time. TSP for P and urea for N were used as source of fertilizer.

Agronomic Data Collection
Flowering and maturity dates (when 50% of the plants were at respective phonological stage), number of branches per plant, plant height, number of pods per plant, number of leaf per plants ,pod length, number of seeds per pod and seed yield were recorded. Three central rows were harvested for determination of grain yield and total biomass.

Soil Sampling and Analysis
The soil samples were air-dried and ground to pass 2 and 0.5 mm (for total N) sieves. All samples were analyzed following standard laboratory procedures as outlined by (Sahlemedhin et al., (2000). Organic carbon and total N contents of the soil were determined following the wetcombustion method of Walkley and Black, and wet digestion procedure of Kjeldahl method, respectively. Available P was extracted by Olsen method (Olsen et al., 1954). Soil texture was analyzed by Bouyoucos hydrometer method. The pH (H 2 O) of the soils was measured in water using pH meter with glass-calomel combination electrode.

Statistical Analysis
The data obtained from soil and crop were statistically analyzed using the PROC ANOVA function of SAS and means were compared using LSD at a probability level of 5%.

Physicochemical Properties of Soil
Soil analysis of the two locations before sowing in two years (Table 1) showed that pH values (5.0 and 5.6) found in the range of strong acid based on Herrera (2005) classification. Whereas the P application were resulted in a significant increase in soil pH compared to two verities, the application P 30 kg/ha led to slight decrease soil acidity in both year1&2, but this was not significant (Table 2). Lime combined with P fertilizer gave the mean highest value of soil pH (6.12) at Dolla site while P fertilizer applied had the least (5.2) at Gununo site. This result clearly indicated that the area is seriously affected by soil acidity, which is not satisfactory for growth of most crops (Havlin et al., 1999). Soil analysis results of soil sample showed that pH values at harvested were higher than values before sowing both in year1&2, which may be attributed to application of P fertilizer and the positive effect of lime in neutralizing acid soils (Table 1& 2).
The range of available phosphorous contents of the two locations (0.6 and 1 mg kg -1 ) before sowing was very low (Table 1); this range was very low based on Herrera (2005). This low concentration of available P may be related to acidity of the soil which bring fixation of P (Havlin et al., 1999). The highest concentration of Av. P (5.2-6.1mg/kg) was recorded under year 2 in Gununo and Dolla site respectively, whereas the lowest Av. P was found at year 1 at two locations. The differences in Av. P concentration in soil might be resulted from changes in biological and geochemical processes at different activities after human disturbances.
Application of P might contributed in releasing some amount of fixed P to be available for the crop. This also indicates that deficiency of P cannot be replaced with other atoms. As a result in acidic soils which are deficient in Av.P, OC and TN are important to apply P together with other nutrients to increase crop production. The same result was obtained in the year1 and 2 of the OC and TN in experiment site. Statistically there was no significant difference on TN and OC of soils in both locations. On the other hand, application of P resulted in significant variation on soil pH and available P in the two locations of year1 & 2. First year and second years P application had affect haricot bean production. This is in agreement with Anetor and Ezekiel (2007) who indicated that lime increased pH and available P in Nigeria. However, potassium and exchangeable acidity were decreased with increasing application. Textural analysis showed that the same textural class according to the present study soil textural class was sandy loam in both locations and in textural class there are no significantly differences between year 1 & 2. The lack of soil textural class difference between year 1 & 2 at both location might be attributed to the similarity in parent material from which the soils originate.

Table 2. Mean value phosphorus on soil chemical properties at Gununo and Dolla, 2012-2013
The changes of soil pH and Av.P of soil may be attributed to the neutralizing of acid soil due to application of lime and also application of P fertilizer at increasing rates (Tisdale et al., 1993). The dates were year 1&2 content of the soil which exhibited an increasing trend with increasing rates of liming material application.

.Effect of phosphorus on growth performance of haricot bean verities
Application of P at different rates resulted in significant variation on growth parameter of plant in the two locations (Table 3). Growth parameters such as plant height, leaf and branches number were increased significantly as the rates of P increased. Maximum values of plant heights, leaf and branches numbers were recorded at application rates of 30 kgPha -1 in the two locations; Hawassa Duma had better performance than Omo-95. In line with this result Kisinyo et al. (2005) indicated that growth of plant increased in acid soil as application of P increased with and without lime. This positive growth response of haricot bean for application of P in acidic soil may be related with better availability of P as the rates of P application increased. Furthermore, plant did have better performance, which may come from the effect of P on soil acidity and in turn improve the availability of P for crops. Similar result was also reported by Singh and Tripathib (1994). Values followed by the same letter (s) within a column are not significantly different at P ≤ 0.05 NS-not significant

Pods number and length
Analysis of variance showed that there was significant effect of phosphorus rates on number and length of pods for both varieties in two locations. Maximum number and length of pods were recorded at rate of 30 kg Pha -1 with verity of Hawassa dume while Omo-95 had lower performance (Table 4). Such increment of pods number and length with increasing rate of P may be attributed to the better availability of P for plants as the rate of external P application increase which in turn observed on better plant performance. Effect of P and haricot bean verities were significant whereas P fertilizer had interaction with haricot bean varieties were significantly (P < 0.05) affected pod number of the hawassa dume verity. Highest number of pods per plant (14. 0) was produced when the crop was grown in 30 kg Pha -.
Finding is also in line with reports of Malik et al. (2006) who indicated more pod number per plant of soybean.

Seeds number and seed yields
There was significant variation on seed number per pod and seed yield ha -1 due to application of phosphorous for the two varieties. Maximum number of seeds per pod and seed yield ha -1 at the two locations were recorded at 30 kgPha -1 for both varieties and seeds number and seed yield were increased with increasing rates of P. So this result indicated that P improves availability of P for crops and also external P application improved crop yield performance. The result may be attributed to the fact that applying phosphorus fertilizer increases crop growth and yield on soils which are naturally low in P and in soils that have been depleted (Mullins, 2001

Table 4. Mean value of phosphorus on yield and yield components performance of haricot bean varieties at Gununo and Dolla in 2012-2013/14
Values followed by the same letter (s) within a column are not significantly different at P ≤ 0.05 NS-not significant

SUMMARY AND CONCLUSION
A field experiments were conducted at the two locations on acidic soil to study the effect of phosphorus application on haricot bean verities at Dolla and Gununo in Wolaita Zone, Southern Ethiopia. The research work was initiated to evaluate the response of haricot bean varieties to different rates of P fertilizer on acid soils. The experiment was laid out in factorial randomized complete block design with three replications. Hawasa dume and Omo-95 were treated by combination of four rates of P (0, 10, 20 and 30 kgPha -1 ). Soil samples were collected from two locations before sowing and at maturity for analysis of some selected physical and chemical properties of soil (texture, Soil pH, Av. P, OC, and TN). Laboratory analysis result of the soil samples taken before sowing and at harvest revealed that all the soil parameters were at lower rates even though the soil was treated by different rates of P. Available Phosphorus was showed increasing tendency with increasing soil pH on both location with two seasons. The overall result of chemical properties in this study, demonstrated that most soil parameters were significantly different with lime application at two areas.
There was a significant increase on growth parameters of the two varieties as rates of P fertilizer increased at both location at Dolla and Gununo. Maximum values of plant height, leaves and branches number were recorded at application rates of 30 kgPha -1 at both location in year 1&2. Similarly, the highest grain yield and yield components were obtained at 30 kg P ha -1 on both varieties at two locations. Generally in the study area; there were strong acidity and low values of some chemical properties of the soil. The application of P fertilizer increased yields of haricot bean; however, the grain yields were low compared with crop potential. This indicates that a two-season treatment of P can correct problem of soil acidity. So it is recommended that correcting of soil acidity should be done for growth seasons until soil comes to neutral conditions and increased crop production.

ACKNOWLEDGEMENT
We are hugely indebted to Wolaita Sodo University for the research work grant (Grant number WSU/2004/01) and for allowing us to do our research concern. We are particularly grateful for the Agricultural Office of Wolaita Zone, Boloso Sore and Damot Sore Rural Development Office for their willingness to give necessary information, guidance and encouragement and for their valuable time. Our thanks go to the development agents working in the researches sites. Therefore, we would like to extend our deepest gratitude to them for their continuous technical support and commitment during the whole path of the research work.
Finally, we are indebted to the Department of Plant Science of Wolaita Sodo University for their contribution in the process of developing the research proposal and provision of various services.