Strawberry ( Fragaria × ananassa Duch . ) yield as affected by the soil pH

Two-year trials (2006-2007) suggested that the use of calcium oxide (CaO) on acid soils increased soil pH and yields in strawberry cultivars Marmolada, Selena and Senga Sengana, under the environmental conditions of Cacak (Western Serbia). The highest yield was obtained when CaO was applied at 750 kg ha–1 rate. Further increase in rate up to 1,500 kg ha–1 did not show corresponding increase in yield; the result was a slight yield drop compared to the peak yield shown at 750 kg ha–1 rate. Overall, yields at rates above 750 kg ha1 were still higher than control and in the treatment employing lowest CaO application rate of 250 kg ha–1.


INTRODUCTION
In Republic of Serbia, strawberries are being cultivated on soils with pH ranging between 4 and 8. Milosevic (1997) shows that acid soils with pH 4.0 are less suitable for strawberry production than alkaline soils with pH 8.0.In these extreme soil pH values strawberry production, yield potential and fruit quality are seriously compromised.According to Milosevic (1997) optimum soil pH for strawberry cultivation ranges from 4.6-6.5.A highly marked increase in substitutional acidity is being exhibited in 22% of soils in Serbia, and 56% of soils have pH values consistent with acid reaction.As reported by Cakmak (2002), 60% of world soils exert limiting effects on food production due to their degradation, micronutrient deficiencies and toxicity traits.
The subject matter of this study is strawberry cultivation on acid soils subjected to treatments aimed at acidity reduction i.e. increasing pH values by CaO ap-plications to the soil.A great number of authors (Gray et al. 1999, Burelle 2003) have studied the effect of soil as a primary substrate on vegetative growth, reproductive cycle, strawberry yield, accumulation of certain elements, particularly heavy metals (Cd), in the roots, leaves and fruits.
The objective of the study was to determine the most favourable CaO rate that would bring soil pH to the level that would insure highest possible yields per unit area.
Several authors (Makus and Morris 1989, Cheour et al. 1990, 1991, Na Phun et al. 1995, 1997, Wojcik and Lewandowski 2003, Lanauskas et al. 2006) have reported seeing positive effects of soil and/or foliar-applied calcium-containing compounds on yield and fruit quality in strawberries as well as on soil pH increase (Takeda 1999, Lacertosa et al. 1999, Niskanen and Dris 2002).Cieslinski et al. (2004) showed that increased soil pH has positive effect on growth and yield in certain strawberry cultivars.The trial was set up as a randomised block design in four replications for a single treatment, with each replication including a control.The experimental plot was 10 m 2 .Adjoining plots were separated with 1 m wide insulating tape.

Trials
In October of 2005 and 2006 CaO was broadcasted by hand immediately incorporated into the soil.CaO treatments were as follows: In March of 2006 and2007, 500 kg of NPK (10:12:26), and 150 kg lime ammonium nitrate (27%) per hectare were incorporated into the soil.Provided plant care was in accordance with the modern strawberry production technology.Soil analysis was done prior to strawberry planting and after the harvest.A Pye glass electrode pH-meter-potentiometer (W.G.Pye, Cambridge) was used to measure the pH value in 0.01 M KCl.
Experimental data were subjected to analysis of variance.For mean separation a Dunett's test at P < 0.05 and P < 0.01 was used.The data were analyzed by the ANOVA statistical program, Origin, version 7.5.Correlation and regression analysis and analysis of the variance of regression at P < 0.05 and P < 0.01 were employed to determine correlation and interaction between the CaO application rate and soil pH change (Mead et al. 1996).
WEATHER AND SOIL CHARACTERISTICS Climate conditions during the examination were not significantly different from the long-term averages.In 2006, the average annual temperature was 9.1 • C, and the average temperature for the growing season was 15.3 • C. The total annual and total growing season precipitations were 561.9 mm m -2 and 343.9 mm m -2 , respectively.In 2007, the average annual temperature was 11.6 • and the average temperature for the growing season was 18.0 • C. The total annual and growingseason rainfalls were 505.4 mm m -2 and 205.0 mm m -2 , respectively.
The planting was established on brown forest soil developed from schist.Prior to establishing the trial planting and calcium-oxide treatments, soil was showing a highly acid reaction (pH 4.12).Soil analysis reviled following nutrient levels: 2.14% humus, 0.14% total nitrogen, 50 mg kg -1 P 2 O 5 and 110 mg kg -1 K 2 O at a depth of 0-40 cm.

RESULTS
Our results indicate that the soil acidity (pH) is affected by the CaO application rate as shown in Table I.
The data analysis showed that high CaO application rates resulted in decreasing soil acidity showing higher pH values as expressed in absolute and relative amounts.The maximum CaO application rate of 1,500 kg ha -1 raised pH readings for 2.10-unit or 33.76% compared to the control.This is also confirmed by the linear regression curve (Fig. 1) with a shape Y = 3.85 + 0.37x and a very high correlation (r = 0.959) coefficient.The regression variance analysis detected statistically significant differences between the soil pH obtained by increasing CaO rates and the control (P < 0.05).
The trial results presented in Table II and Figure 2 show that the use of CaO for raising the soil pH had positive effect on strawberry yields.The yields obtained in all the treatments were higher than those in the control.The highest yield in all cultivars examined was obtained in the trial plot where 750 kg ha -1 CaO (A 4 ) was applied.At this rate there was an increase in pH from 4.12 (the control) to 5.75, as well as the increase in yield of 124.63%.Data in Table III show strawberry yields obtained in the control (A 1 ), being 10.60 t ha -1  in Marmolada, 9.65 t ha -1 in Selena and 8.50 t ha -1 in Senga Sengana cultivars.With the highest-yielding A 4 treatment, the yield varied from 19.70 t ha -1 (Senga Sengana), 21.75 t ha -1 (Selena), and 23.12 t ha -1 (Marmolada).Compared to control the highest yield increase was recorded in Senga Sengana (131.76%),followed by Selena (125.36% and Marmolada (118.11%).The analysis of variance and the Dunett's test showed statistically significant (P < 0.01) increase in maximum yields compared to control with the CaO application rate of 750 kg ha -1 .

DISCUSSION
This study supports data cited in literature (Milosevic 1997, Niskanen andDris 2002) that the most favourable pH for t strawberry production is between 4.6 and 6.5.Similar data were reported by Cieslinski et al. (2004) who determined that pH 5.1 and pH 6.8 had different effects on plant development and strawberry yield -better tiller development and higher yield at higher soil pH in strawberry cultivars (Rainier, Totem and Selva) grown under greenhouse conditions in Parkhill sandy loam soil.
Further CaO application rate increase exceeding 750 kg ha -1 resulted in a gradual yield decrease.The observation can serve as an important indicator in strawberry production on acid soils.Importantly, the yield evidently decreased with respect to the 750 kg ha -1 CaO application rate (A 4 ) but increased as compared to the control (A 1 ) and the lowest rate treatment (250 kg ha -1 CaO).Lanauskas et al. (2006) determined that 150 kg ha -1 Ca(NO 3 ) 2 applied to the soil were not sufficient to justifiably increase the yield and fruit weight of the Honeoye strawberry cultivar as compared to the control (without fertilisation) on the soil with the pH of 7.1.According to Brocic (1997) 4,000 kg ha -1 CaO are required to decrease acidity by 0.7 pH units on pseudogley, being eight times the rates applied in this study which caused similar changes in pH.The differences are likely to be due to soil types, as the soil in our study is brown forest soil developed from schist, that is far more fertile and richer in organic and mineral matter than pseudogley soil.The climatic conditions in the research years were nearly identical thus they could not have markedly affected studied parameters.
Strawberry cultivars in all treatments received identical nutritional regime involving the applications of NPK (10:12:26) at the rate of 500 kg ha -1 , and 150 kg ha -1 lime ammonium nitrate therefore nutrient management was not responsible for the yield increases.The yield increase as induced by the use of different CaO rates on acid soils may be attributed to the effect of soil pH and Ca 2+ ions on the mobilisation and uptake of certain ions from the soil by the strawberry root system.

CONCLUSION
The obtained results from the study on the effects of increasing CaO rates on soil pH change and straw-   berry yield may suggest the following conclusions: the use of CaO on acid soil increased soil pH and yield increases in Marmolada, Selena and Senga Sengana strawberry cultivars in all treatments applied.The highest yield was recorded with the 750 kg ha -1 CaO application rate, with pH of 5.75.The increase in CaO rates above 750 kg ha -1 did not bring corresponding increase in strawberry yield while showing slight decreasing tendency with respect to the rate mentioned.Overall at CaO rates above 750 kg ha -1 yield was higher than in the control (0 kg ha -1 ) and the treatment employing the lowest application rate (250 kg ha -1 ).Palavras-chave: solos ácidos, CaO, pH, morango, produtividade.

RESUMO
were conducted in 2006 and 2007 in a strawberry planting at Prislonica situated 15 km north-east of Cacak (43 • 53 N; 20 • 21 E), Western Serbia at an altitude of 530 m.The research material included most commonly grown strawberry cultivars Marmolada, Selena and Senga Sengana.The cultivars were grown as "frigo" seedlings planted at the beginning of August in 2005 and in 2006 in simple rows at 80 × 25 cm spacing (50,000 seedlings per hectare).The flowers were cut back in autumn.

TABLE III Yield of strawberry cultivars obtained in the control (A 1 ) without CaO application and in the A 4 treatment with 750 kg ha -1 CaO which resulted in the highest yield.
Fig. 2 -Influence of soil pH changes on yield.An Acad Bras Cienc (2009) 81 (2) STRAWBERRY YIELD AS AFFECTED BY THE SOIL pH 269