Effect of lime and phosphorus fertilizer on acid soil properties and barley grain yield at Bedi in Western Ethiopia

Soil acidity associated with soil fertility problems are the main constraints hindering barley production in most highlands of Ethiopia. Field experiment was conducted to evaluate effects of lime and phosphorus (P) fertilizer application to acid soils on grain yield of barley and soil chemical properties during 2009 to 2013 cropping seasons at Bedi in Western Ethiopia. The experiment was laid out in randomized complete block design with three replications. Five levels of lime (0, 0.55, 1.1, 1.65 and 2.2 t/ha) and four levels of P (0, 10, 20, and 30 kg/ha) were combined in a complete factorial arrangement. Lime requirement of the soil was calculated based on its exchangeable acidity. The combined analysis over years showed significant improvement of barley grain yield and soil chemical properties due to the main and interaction effects of lime and phosphorus. Grain yield was progressively increased with incremental levels of lime and Phosphorus application. The highest yield was obtained from 2.2 t/ha lime application coupled with 30 kg/ha phosphorus fertilizer, but on par with 1.65 t/ha lime and 20 kg/ha phosphorus application. Grain yield is increased by 274.0% with 1.65 t/ha lime and 20 kg/ha Phosphorus application in the initial year compared with control; however, this yield increment declined over years and reached 99.5% after five years. This yield reduction after five years of lime application may indicate re-acidification of the soil which warrants re-liming. In this study, lime application was the major source of variation for soil chemical properties. Soil pH was sharply increased by liming with the highest value (5.9) and thereafter slightly declined to 5.3 over five years. Exchangeable acidity decreased significantly with increase in lime application to as low as 0.1 cmol/kg, while available P and exchangeable Ca 2+ were noticeably improved. Hence, lime application at the rate of 1.65 t/ha coupled with 20 kg/ha Phosphorus fertilizer could sustainably enhance barley production on acid soils of Bedi and similar areas with likely re-liming of the soils, every five years.


INTRODUCTION
Soil acidity is a major environmental and economic concern in many areas of Ethiopia which causes significant losses in crop production.Soil acidity is a complex of several factors involving plant nutrient deficiencies and toxicities, low activities of beneficial microorganisms, and reduced plant root growth which limits absorption of nutrients and water (Fageria and Baligar, 2003).Poor crop production on acidic soil has long been associated with aluminum (Al 3+ ) toxicity, reduced nodulation or mycorrhizal infections and low phosphorus (P) availability (Kochian et al., 2004;Wang et al., 2006).
Soil acidity and Al 3+ toxicity in surface soil can be ameliorated through liming (Fegeria and Baligar, 2008;Rebecca et al., 2010).Changes in soil pH brought about by liming may have profound effects on the availability of many elements absorbed by crops.Liming increases soil pH and thus decreases Al 3+ and Mn toxicities which also increase NO 3 -N, Ca and P availability (Arshad and Gill, 1996;Caires et al., 2005).
In Ethiopia, large areas of highlands with altitude of >1500 m located in almost all regional states of the country are affected by soil acidity.According to Ethiosis (2014) about 43% of the Ethiopian arable land is affected by soil acidity.Also, Mesfin (2007) reports that moderately acidic soils with pH less than 5.5 considerably influence crop growth and require intervention.The main factors giving rise to increased soil acidity in Ethiopia include climatic factors such as high amount of precipitation (that exceeds evapo-transpiration which leaches appreciable amounts of exchangeable bases from the surface soil), temperature, severe soil erosion, morphological and anthropological factors.The largest areas of the Western Oromia highlands are dominated by Nitisols with high acidity (Mesfin, 1998;Temesgen et al., 2011).
Barley (Hordeum vulgare L.) is the dominant cereal crop grown in the high lands of Ethiopia where soil acidity is rampant.Barley production covers a total area of 1.02 million ha with a national average productivity of 1.87 t/ha (CSA, 2014).Soil acidity is considered to be one of the major bottlenecks to barley production in the highlands of Ethiopia.The problem still persists and has not been addressed sufficiently.Consequently, small-scale farmers in the highlands of the country have almost given up barley production to the severe soil acidity.Farmers practice barley-bare fallow-oats rotation system reduces the negative effects of soil acidity and improve soil fertility (Hailu and Getachew, 2011).However, this rotation system is not sustainable and in the long run will degrade the soil resource due to severe soil erosion on the bare fallow.Farmers are not encouraged to apply P fertilizer due to low response to P application as a result of P fixation.
Phosphorus reacts with Fe and Al oxides/hydroxides under acidic conditions to form insoluble phosphates, hence reducing P availability to plants (Kamprath, 1984).Phosphorus deficiency often, therefore, occurs simultaneously with Al 3+ toxicity in these soils.Efforts to ameliorate the deleterious effects of soil acidity must therefore be accompanied by measures to increase available P in soils.Addition of lime to acid soils has long been widely adopted as, the amelioration strategy for many years to improve crop production which is rarely used in Ethiopia.
Appropriate combination of lime and P fertilizer is therefore an important strategy for improving crop growth in acid soils.There is however, scarcity of information on interactive effects of lime and P fertilizer application on crop performance in western Ethiopia.The objective of this study was therefore, to investigate the interactive effects of lime and P fertilizer on barely grain yield and soil chemical properties under acid soil condition in Western Ethiopia.

Study site
The study was conducted for five consecutive years during 2009 to 2013 main cropping seasons at Bedi in western Ethiopia.Bedi is located on longitude 9°05' N, latitude 38°36' E and 2565 m altitude in the central highlands of Ethiopia (Figure 1).The site is typically characterized by plains with cool subtropical climate.
The area receives an average annual rainfall of 1100 mm with bimodal distribution of January to March (small rain) and June to September (major season).The soils are classified as Nitisols with deep, red, and well-drained tropical soils.The following criteria were set for selecting suitable site: the soils should be fairly well representative for barley production in the area; the soil should have pH values of lower than 5.5, and the soils should have no previous liming history.Some of the physical and chemical characteristics of the experimental site are summarized in Table 1.

Experimental design and procedures
The experiment was laid out in a randomized complete block design with three replications.Five levels of lime (0, 0.55, 1.10, 1.65, 2.20 t/ha) and four levels of P (0, 10, 20, and 30 kg/ha) were combined in a complete factorial arrangement.Lime requirement of the soil was calculated based on its exchangeable acidity (Al 3+ plus H 1+ ) adapted from (Kamprath, 1984).
The aforementioned five levels of lime correspond to 0, 50, 100, 150 and 200% of the lime are required to neutralize the exchangeable acidity of the soils.Good quality commercial grade agricultural lime (CaCO3) with 98% neutralizing value and <250 µm in diameter was used.Lime was applied uniformly in broadcast by hand to every plot a month before sowing and soil incorporated by oxen plowing only in the initial year.The experimental plots were kept permanent to observe the residual effects of lime application over years.
Triple super phosphate (TSP) and urea were used as inorganic fertilizer sources and applied every year.The entire dose of TSP was applied at planting, while the recommended N rate (46 kg/ha) was applied in split, viz: half at sowing and the remaining half side dressed at tillering stage of barley.Gross and net plot sizes were 4

Soil sampling and analyses
Composite surface (0 to 20 cm) soil samples were collected from each plot and analyzed for soil physical and chemical properties during the initial year and subsequent alternative years.A 5 cm diameter auger was used to sample five randomly selected spots per plot.These sub-samples were thoroughly mixed, homogenized, air dried under shade, ground and passed through a 2 mm sieve.The samples were analyzed for soil texture, pH, available P, total N, organic carbon, exchangeable acidity Al +3 , exchangeable cations (Ca 2+ , Mg 2+ , K + , Na + ) and cation exchange capacity (CEC) using the procedures outlined in Page et al. (1982).

Statistical analysis
Analysis of variance was conducted for each year separately and combined analysis over the five years.Analyses of variance were performed using the Statistical Analysis System (SAS) statistical program (SAS V8.2, SAS Institute Inc., Cary, NC, USA).Whenever the ANOVA detected significant differences between treatments, mean separation was conducted using least significant difference (LSD).Pearson correlation coefficients were also used to assess the significance of the relationships between yield and some soil properties.

Grain yield
The factorial analysis of variance indicated that lime and P fertilizer application significantly (P<0.05)affected barley grain yield in each year (Table 2).However, interaction effect of lime and P fertilizer application on grain yield of barley was found significant only during the initial three consecutive years.The combined analysis of variance over years showed highly significant (P<0.05)lime, P, lime × P interaction effects on barley grain yield (Table 2).
In general, progressive increases in grain yields were recorded with incremental levels of lime and P fertilizer application.Grain yield response was found more pronounced with the first than the second increment of lime and P application.The highest barley grain yields in each year and combined analysis were obtained from the  2).Mean barley grain yield increment in the combined analysis at 1.65 t/ha lime coupled with 20 kg/ha P application was 183.5% cf.control.
Similarly, in the initial year of 2009 grain yield increment was 274.0%cf.control, but in subsequent years grain yield advantage has steadily decreased to 224.0, 174.9, 164.0 and 99.5% in 2010, 2011, 2012 and 2013, respectively.In a nutshell, the effect of lime on acid soil amelioration and barley grain yield were the highest during the initial four years, but in the final year grain yield was declined substantially.This yield reduction in the final year may indicate re-acidification of the soil.It is thus perceived that maximum amelioration of acid soils with lime could be achieved only after the elapse of four years since reacidification would probably balance the slower amelioration reaction associated with less reactive lime particles.Meng et al. (2004) reported that crop yield increment at 50, 100, 150 and 200% lime application rates were lasted for 5, 7, 12, and 14 years, respectively.The present findings are in agreement with Farhoodi and Coventry (2008), who reported that a year after lime application resulted in substantial yield increments of barely, wheat and faba beans (70 to 75%), and durum wheat at about 30%.Many researchers also revealed that lime application improved grain yield of crops (Liu et al., 2004;Achalu et al., 2012;Caires et al., 2005).According to Achalu et al. (2012), the increase in crop yield through application of lime may be attributed to the neutralization of Al 3+ , supply of Ca 2+ and increasing availability of some plant nutrients like P. Furthermore, increase in grain yield with the application of lime is ascribed to its favorable effect on the chemical, physical, and microbial properties of the soil.Numerous authors (Scott et al., 1999;Farhoodi and Coventry, 2008) reported that application of lime at an appropriate rate brings about several chemical and biological changes in the soil, which is beneficial to improve crop yields in acid soils.
In the present study, the higher grain yield realized from calcitic lime application during the initial four years indicates fast dissolution reaction and high acid neutralization capacity of calcite lime.Similar behavior and performance were reported by other researchers about the fast dissolution and high reactivity of calcite (Hartwig and Loeppert, 1992), as well as its high effect (Bailey et al., 1989), and high solubility in acid (Merry et al., 1995).

Changes in soil chemical properties
The results of soil analysis in 2009, 2011 and 2013 showed that lime application had significantly (P<0.05)increased soil pH and available P, while exchangeable acidity and Al 3+ had significantly reduced (Table 3).Soil pH was sharply increased by liming in the first year and thereafter slightly declined over years.Increasing lime application rates resulted in increase in soil pH values.
Application of 2.2 t/ha lime increased soil pH from the initial 4.8 to 5.9 in 2009, but on par with 1.65 t/ha lime applications with pH value of 5.66.Subsequently, after five years of lime application soil pH dropped to 5.3.Essentially, amelioration of soil acidity comprises detoxification of Al and Mn activity with the aid of lime amendment.Detoxification of Al can be achieved by increasing soil pH which in turn certainly result in Exchangeable Al only becomes significant at pH levels less than 5.5 (Cregan, 1980) and the Al 3+ cation can be toxic to roots which is one of the major reasons that soil acidity can affect plant growth (Fenton and Helyar, 2007).The present findings are in agreement with Murata et al. (2002) who reported that application of lime at the rate of 2 t ha -1 significantly increased topsoil pH values from 4.6 to 6.0.Meng et al. (2004) also showed soil pH increment of 0.64 to 2.14 units due to lime application which values were maintained for five years, while pH of the limed soil remained above the initial pH value up to 15 years.
In concomitance with increase in soil pH, available P level was also improved.Application of 2.2 t/ha of lime was on par with 1.65 t/ha in increasing available P in all years except in the initial year 2009.In a nutshell, application of lime improved P availability by 77.6, 40.0 and 36.6% as compared to no liming in 2009, 2011and 2013, respectively. Sven et al. (2015) ) showed an increase in P availability with comparable amounts of added lime in field trials.Sarker et al. (2014)  + ions from the soil sorption sites resulting into reduction in soil acidity and P fixation.In general, on acid soils with a low initial pH, it can be expected that extractable P increases after lime application.This is due to the increase of the pH, causing desorption of P from Fe-oxides, Al-oxides and -hydroxides and the dissolution of Fe and Al-phosphates (Haynes, 1984).Application of lime and its residual effect highly decreased exchangeable acidity and Al +3 as the level of applied lime rates increased.Interestingly, all lime rates significantly (P<0.01)decreased exchangeable acidity from the initial level of 1.32 to 0.1 cmol/kg (Table 3).As could be expected, the effect of lime on exchangeable Al 3+ was almost similar to that of exchangeable acidity.Meng et al. (2004) reported similar findings with surface application of lime; acidity, particularly exchangeable Al 3+ , was significantly reduced from 5.46 to 1.52 cmol/kg in the first year and these values are maintained up to five years which gradually increased to the original level after 14 years

Relationships between grain yield and soil properties
Barely grain yield was positively correlated with soil pH and available P and inversely correlated with exchangeable acidity and exchangeable Al 3+ and the correlation was significant at P<0.01 (Table 4).However, grain yield was correlated most strongly with soil pH (r = 0.93), available P (r = 0.86), and exchangeable Al 3+ (r = -0.86).This illustrates that available P and soil pH and exchangeable Al 3+ are the most important yield limiting factor in acid soils.
Similarly, positive and significant correlation coefficients were observed among soil properties of each other.The data also revealed a strong and inverse correlation between exchangeable Al 3+ and Ca 2+ (r = -0.90).The positive correlation of soil pH with the grain yield implies that as the pH increases the yield also increase and as the

Figure 1 .
Figure 1.Bedi site and acid soil map of Ethiopia.

Figure 2 .
Figure 2. Effect of the combined use of lime and phosphorus fertilizers on the grain yield of barley Pooled over five years.The perpendicular line drawn shows optimum lime and P rate where maximum grain yield was achieved.

Table 1 .
Some physical and chemical soil characteristics of the Nitisols at Bedi site before commencement of the experiment.

Table 2 .
Effects of lime and phosphorus fertilizer application on grain yield of barley (kg/ha) at Bedi during 2009 to 2013 cropping seasons.
application of 2.2 t/ha lime and 30 kg/ha P which was on par with 1.65 t/ha lime and 20 kg/ha P application, suggesting increasing lime and P application beyond this rate is not worthwhile in terms of grain production (Figure

Table 3 .
Lime and its residual effects on soil pH, available P and exchangeable acidity at Bedi during 2009 -2013 cropping seasons.