Variation of liming recommendation caused by calculation approach

Z. Loncaric, K. Karalic, V. Vukadinovic, B. Bertic and V. Kovacevic

Faculty of Agriculture, University of Osijek, Trg Sv. Trojstva 3, HR-31000 Osijek, Croatia (e-mail: )

Key words: hydrolitic acidity, pH, cation exchange capacity, soil acidity

Abstract

Acid soils are widespread in the Eastern Croatia with acidity as limiting factor of the field crops yield. The widely accepted ameliorative measure for acid soils is liming with goal to increase soil pH. The liming recommendations are based on different soil properties and therefore the calculation could differ according to available and used soil data. The acid soils are sampled on a hundred different sites in Eastern Croatia and analyzed: pH (H2O), pH(KCl), Hy and CEC. The bases saturation of CEC were calculated, as well as liming recommendations using target soil pH or target BS as a base of calculation. The maximum difference caused by calculation approach for target BS = 80 (or pH = 6,0) was 4,36 t ha-1 (30% of higher recommendation), minimum difference 0,08 and in average for 100 samples 1,53 t ha-1. For target BS = 90 (or pH = 6,5) all the recommendations were higher than previous one, but the differences were lower (maximum 2,18 t ha-1, minimum 0,04 and in average 0,76 t ha-1). Comparison of two approach of calculating liming recommendation lead to conclusion that the differences (what means possible errors) are higher when the target pH or BS is lower.

Introduction
Soil acidification is a slow, continuos natural process resulting in acid soils being common in areas where soil development continued for long, geological periods of time and under climatic conditions which rainfall exceeds evapotranspiration (Rengel, 2002). The process of soil acidificationis aided by water leaching base cations to lower horizons, and acid soils are therefore widespread in the Eastern Croatia with acidity as limiting factor of the field crops yield (Kovacevic et al. 1993). Human activities may intensify and speed up the acidification process. The widely accepted ameliorative measure for acid soils is liming with goal to increase soil pH. The liming recommendations are based on different soil properties and therefore the calculation could differ according to available and used soil data.
Material and methods
The acid soils are sampled on a hundred different sites in Eastern Croatia and analyzed in order to collect soil data for different liming recommendation calculations. Soil analyses included most often methods used for soil fertility control and liming recommendations in Croatia: pH (H2O and M KCl, 1:5 v/v) (ISO, 1994), hydrolitic acidity by Na-acetate extraction (Vukadinović and Bertić, 1988), cation exchange capacity by ammonium-acetate extraction (Jones, 2001), soil organic matter content by sulphochromic oxidation (ISO, 1998) and plant available phosphorus and potassium by ammonium-lactate extraction (Egner et al. 1960). / Results and discussion
The range of pH (H2O) in analyzed samples was 4,75-7,18 and range of pH (KCl) 3,48-6,17. Hydrolitic acidity (Hy) ranged from 0 to 8,97 cmol (+) kg-1 and CEC from 5,38 up to 37,25 cmol (+) kg-1.
The bases saturation (BS%) of CEC were calculated using equation:
BS % = 100 - (Hy × 100 / CEC) (1)
The range of BS was 24,27% to 100%. The distribution of samples in ranges according to soil analysis shows that the most number of samples had hydrolitic acidity in range 3-6 and low CEC in range 5-15 cmol (+) kg-1 (Table 1).
Very significant correlations were determined between soil pH, hydrolitic acidity and base saturation of CEC, as was expected (Table 2.). But, these data and equations are used for comparison of liming recommendation calculated with two different equations common in Croatia.
Significant correlation between pH and base saturation of CEC (BS) showed that both, pH and BS, could be used as liming target value and compared using equation:
BS % = -31,41 + 18,86 × pH (H2O) (2)
or
BS % = 7,05 + 15,84 × pH (KCl) (3)
Appropriate values of pH (H2O), pH (KCl) and BS used for calculation of liming recommendation are shown in table 3.

Table 1. Maximum and minimum values and percentage of analyzed samples according to soil properties values

pH(H2O) / pH(KCl) / Hy / CEC / % BS
min / 4,75 / min / 3,48 / min / 0 / min / 5,38 / min / 24,27
max / 7,18 / max / 6,17 / max / 8,97 / max / 37,25 / max / 100,0
% / % / % / % / %
4,75-5,5 / 36 / 3,48-4,5 / 55 / 0-3 / 36 / 5-15 / 46 / 24-50 / 11
5,51-6,5 / 47 / 4,51-5,5 / 36 / 3-6 / 52 / 15-25 / 43 / 50-75 / 33
6,51-7,5 / 17 / 5,51-6,5 / 29 / 6-9 / 12 / 25-40 / 11 / 75-100 / 56
Table 2. Correlation coefficients (r2, n=100)
pH(H2O) / pH(KCl) / Hy / CEC
pH(KCl) / 0,876
Hy / -0,762 / -0,804
CEC / 0,613 / 0,445 / 0,260
BS / 0,855 / 0,781 / 0,861 / 0,641
Table 3. Appropriate values of pH and BS calculated by regression and used for liming recommendation
pH (H2O) / pH (KCl) / BS %
7,0 / 6,0 / 100
6,9 / 5,9 / 99
6,5 / 5,5 / 90
6,0 / 5,0 / 80
The liming recommendations are calculated using target values of two different soil properties: soil pH or BS.
Soil pH as target value was used according to formulas for t/ha CaCO3 for liming up to target pH = 7 (Finck, 1982):
t/ha = 50,04 × depth (cm) × ρv (kg dm-3) × Hy/1000 (4)
and using that result in formula for liming up to target pH:
(5)
The pH values in formula (5) is related to pH in H2O, and if the target and measured values are for pH in KCl (according to table 3), than the number 7 in formula (5) should be replaced with number 6 (as pH in KCl for soil with BS = 100).
The second soil properties used as target value was bases saturation of CEC (BS%). This calculations contain two steps like the previous one. The first step is to calculate amount of hydrolitic acidity which should be nutralize to achieve target BS:
Hy to neutralize = Hy – CEC × (1-target BS/100) (6)
The second step use that result for calculation CaCO3 amounts (t ha-1) needed for application on desired soil depth (in cm) and related to soil volume density (ρv):
t CaCO3 ha-1 = depth (cm) × ρv (kg dm-3) × (6) / 20 (7).
There were no differences in results for liming to target pH=7 or target BS=100 regardless to calculation approach: using formulas (4) - (5) or (6)-(7). But, there were differences in liming recommendation calculated according to target pH or adequately target BS. The example of calculated amounts for 7 samples is shown in table 4, and soil properties for the same samples are in table 5.
The maximum difference caused by calculation approach for target BS = 80 (or pH = 6,0) was 4,36 t ha-1 (30% of higher recommendation), minimum difference 0,08 and in average for 100 samples 1,53 t ha-1. For target BS = 90 (or pH = 6,5) all the recommendations were higher than previous one, but the differences were lower (maximum 2,18 t ha-1, minimum 0,04 and in average 0,76 t ha-1). / Table 4. Calculated liming recommendations using different target soil properties (in t CaCO3 ha-1)
no. / target
BS=80
pH=6,0 / target
BS=90
pH=6,5 / target
BS=100
pH=7,0 / used formulas
1 / - / 5,89 / 11,90 / (6) - (7)
1,08 / 6,50 / 11,91 / (4) - (5)
2 / - / - / 5,13 / (6) - (7)
- / - / 5,13 / (4) - (5)
3 / 3,06 / 7,58 / 12,11 / (6) - (7)
1,00 / 6,56 / 12,11 / (4) - (5)
4 / 1,33 / 4,34 / 7,36 / (6) - (7)
2,18 / 4,77 / 7,36 / (4) - (5)
5 / 8,54 / 11,40 / 14,27 / (6) - (7)
7,93 / 11,10 / 14,28 / (4) - (5)
6 / - / - / 1,53 / (6) - (7)
- / 0,44 / 1,53 / (4) - (5)
7 / 13.79 / 16.49 / 19.19 / (6) - (7)
10.06 / 14.63 / 19.21 / (4) - (5)
Table 5. Soil properties for selected samples
no. / pH(H2O) / pH(KCl) / Hy / CEC / BS
1 / 5.90 / 4.18 / 5.29 / 26.74 / 80.22
2 / 6.82 / 5.47 / 2.28 / 37.25 / 93.88
3 / 5.91 / 3.96 / 5.38 / 20.11 / 73.25
4 / 5.58 / 4.66 / 3.27 / 13.39 / 75.58
5 / 4.75 / 3.77 / 6.34 / 12.73 / 50.20
6 / 6.30 / 5.51 / 0.68 / 10.66 / 93.62
7 / 4.90 / 3.77 / 8.53 / 12.00 / 28.92
Comparison of two approach of calculating liming recommendation lead to conclusion that the differences (what means possible errors) are higher when the target pH or BS is lower.
References
Egner, H., Riehm, H., Domingo, W.R. (1960): Untersuchungen über die chemische Bodenanalyse als Grundlage für die Beurteilung des Nahrstoffzustandes der Boden II. Chemische Extractionsmetoden zu Phosphor- und Kaliumbestimmung. K. Lantbr. Hogsk. Annlr. W.R. 26, 199-215.
Finck, A. (1982): Fertilizers and Fertilization. Introduction and Practical Guide to Crop Fertilization. Verlag Chemie. Weinheim. Deerfield Beach, Florida. Basel.
ISO (1994): International Standard. ISO 10390. Soil quality – Determination of pH.
ISO (1998): International Standard. ISO 14235. Soil quality – Determination of organic carbon by sulfochromic oxidation.
Jones, J.B.Jr. (2001): Laboratory guide for conducting soil test and Plant analysis. CRC Press. Boca Raton, London, New York, Washington. USA.
Kovacevic V, Bertic B and Grgic D 1993 Response of maize, barley, wheat and soybean to liming on acid soils. Rostlinna Vyroba 39 (1), 41-52.
Rengel, Z. (2002): Role of pH in Availability of Ions in Soil. In: Handbook of Plant Growth. pH as the master Variable. Ed. Z. Rengel. Marcel Dekker, Inc. New York, Basel. pp. 323-350.
Vukadinović, V. and Bertić, B. (1988): Praktikum iz agrokemije i ishrane bilja. Poljoprivredni fakultet Osijek.

2