Spatial Variability of pH and Lime Requirement for Sustainable Irrigation of Cross River State Soils

Spatial Variability of pH and Lime Requirement for Sustainable Irrigation of Cross River State Soils

Obot Ekpo Essien

Department of Agricultural/Food Engineering

University of Uyo, Uyo Nigeria

Effiong Essien Una

Formerly, School of Applied sciences, Polytechnic of Calabar,

Cross River State, Nigeria

Abstract

Soil pH in 34 representative sites across all Local Government Areas (LGAs) in Cross River State, Nigeria were investigated using electrometric method at field surveys. Data were statistically analyzed for descriptive statistics using SPSS version 17. Lime requirement was made by filtration. The pH varied between 5.89 and 6.98 making the soils spatially homogenous and fairly acidic (CV = 1 7%). Lime requirement for increasing soil pH were plotted on graphs and predictive functions gave second order polynomials with R2 = 0.8895 to 0.9951. The average amount (mls) of lime per 100g of soil for unit increase in soil pH, using approximately linear spatial variation, varied between 0.0257ml/unit pH change in Usunutong in Ugep LGA to 0.0605 in Ediba in Ugep LGA, 0.066 in EfutAbua, Calabar LGA and to 0.0703 in ObomItiat, Odukpani LGA. A peak value of 150ml of lime was considered the maximum to cause acidic change to pH pf 7.6 8.2. The quality of irrigation water must consider this pH distribution and avoid or amend acid rainfall or water effect to sustain tree crops (rubber), rice and vegetable productivity.

1. Introduction

   Soil is the medium of root development for plants. The organoleptic properties of themedium, the trace elements, the micro and macro nutrients are

   sourcesof soil aggregate sustenance for root stability and food for crop sustenance. On many of these soils the soil pH changes much and becomes low below the neutral pH level. Such low pH has adverse consequences on the soil productive capacity and the crop. Low pH soils have their soil pH below 5.5. This might result in:

   1. Reduction of crop yield, (2) damages to the crop themselves.

      When the pH is less than neutral pH, the availability of micronutrients of manganese (Mn), aluminium (Al) and iron (Fe) increase and this condition might allow toxicity problem of the micronutrient to occur[15].

      The problem of low soil pH is enormous, conversely, the availability of essential nutrients such as K, Ca and Mg, is decreased when essential nutrients become low deficiencies might results in crop which condition reduces productivity hence imposes economic problem.

      Low pH caused by many natural factors. These include: production of more H+ in the soil relative displacement of cations by cations of Aluminum.

      • Inappropriate fertilization by ammonium fertilizer and acidic irrigation water.

      • Intensive fertilization with NH4 based fertilizer and Urea may lower soil pH.

      • High rainfall conditions on soils also leach displace ionic elements of micronutrients, so that soils under high rainfall become more acid that soils formed under dry conditions [1].

      • Soil formed under the native forest vegetation of which a vast proportion in Cross River state is in forest reservation, is said to affect soil pH in such a way that it tends to be more acidic [15].

      • Soil organic matter left on top soils are decomposed by soil micro-organisms varmints and termites resulting in more H+ ion brelease so that the soil becomes more acidic [15].

      On the other hand, lime applications to acid soils increase soil pH and exchangeable Ca and Mg levels and decrease exchangeable acidity levels [3]. This significant increase in total cations with liming is the consequence of lime increasing [9]. The capacity of the soil to retain nutrients (which means increase in effective cation exchange capacity, CEC), and is a beneficial effect of humming to agricultural productivity and economic land use.

      Effect of pH on irrigation is observed when using acidic water on low acidic or any acidic soils. Irrigation water that has a low buffering capacity (or low HCO3 content) might drastically decrease pH levels in crop growing media when used on acidic soil [15]. Irrigating with such water can also decrease the lime requirement for plant production and can cause adverse plant growth by excessively raising the pH of the soil [6]. Therefore to improve productivity, an adequate source of irrigation water must be available to increase the pH or reduce negative changes on soil surface so that the soil retain the needed soil nutrient. The most commonly used technique to raise the soil pH is by applying agricultural lime [15]. The amount of lime required is dependent on the soils natural acidity [5]. Therefore, the knowledge of soil pH is paramount to soil nutrient management and lime requirement or liming potential of the irrigation water for pH moderation. These predicates invite research to establishing the soil pH. Therefore the objective of the research were:

      1. To carry out field survey on pH of representative soils in Local Government Area of Cross River state agricultural zones

      2. To establish lime requirements that influence irrigation water quality selection, crop selection and nutrient management on Cross River Soil.

2. Material and Method

   Sampling: With a shovel and a digger profile pits were dug and the horizon was 15cm (6) deep. Enough soil sample were taken at each pits. The pits were separated by an interval of about 1 kilometer, and 10 of this were bulked into 1 bag to make up one sample similar to the method of Rubins. That is, each pit provided a sub sample, ten of this sub-samples gave out sample. Five samples were obtained in each local government area, this means that 50 pits were dug, fifty sub-samples

   were collected in each Local Government Area. Plate 1 shows the map of Cross River state where the survey was carried out.

   A depth of 15cm was chosen since this is the depth at which most of the agricultural vegetable crops grow [11]. Starting from Akamkpa samples were collected all over the state at the same interval. Altogether 85 samples were taken, that is, 850 sub-samples for the whole state. Each sample was differentiated from the other by the name of the village and the local government area where they were collected. Analysis of these soil samples were also carried out separately. ANOVA was applied to determined variance differences or homogeneity so that similarity of treatment and crop selected can be used. The descriptive and inferential statistics used SPSS version 17 software (Word) for processing.

   1. Determination of pH (Acidity) was done by electrometric method.

      Portion of each sample was air-dried and passed through 2mm sieve. Then 20gm of this soil was placed in 50ml beaker and 20mls of distilled water added. The determination of this pH was by the method of Davis [4]. The glass electrode of the pH meter was inserted into the partly settled suspension and measured. With each sample four readings were taken and the average pH recorded. This is soil pH measured in water. Before the pH meter was used, it was standardized with a standard solution. The distilled water used was also measured and its pH was exactly 7.0.

   2. Lime Requirement Determination

   Whether or not liming is necessary and how much lime is needed to be applied is from the results of a soil test conducted at a state or commercial laboratory [16]. The spatial survey was done to test spatial variability of soil pH and lime requirement, because individual soils can differ greatly in heir lime requirement, which is the amount if lime required to raise the pH to some specified level between 6.0 to 7.0 [16].

   One gramme of calcium oxide was dissolved in distilled water and made up to 1000mls. Portions of 5mls, 20mls, 30mls, 40mls and 50mls were added separately to six 100mls beaker each containing 10gm of air dried sample soil. The volumes of the solution were increased by the addition of water so that the ratio of soil to water was 1:5.

   The seventh beaker blank, had no solution of calcium oxide, rather 50mls of water were added to the 10gm of soil. The whole seven beakers were covered tightly and allowed to

   e

   Plate 1: Cross river state showing soil survey

   remain for 3 days. At the 3rd day the pH of each beaker containing the sample soil were measured and the result used to plot the lime requirement curve against 100gm of soil.

   The method employed here is that of Peech [8]. The amount of mill equivalence of Calcium Oxide per ml can be calculated from the equation.

   Me = 10X x 1000 E V

   where X is the amount of calcium oxide dissolved in water, E is the equivalence and V is the volume of calcium oxide solution. According to Chapmann and Pratt in [14], 1 ml of calcium Oxide on the graph is equivalent to 158.76 kg of Lime per acre assuming the lime is mixed with 9.072 x 105 kg soil per acre.

3. Results

   Results of the field survey of pH at different representative agricultural zones in Cross River state were obtained and average pH for soils in representative Local Government Areas of the State are indicated in Table 1. The pH were clustered into areas with similar values or homogenous distribution. Their comparisons of the lime requirement for the pH of soils were plotted into graphs showed in Figs. 1, 3, 5, 7, 9, 11. The mean

   lime requirement/pH of soils were also compared using bar charts to visualize the difference. These are shown in Figs 2, 4, 6, 8, 10, 12. The lime requirement for the different soil pH of the agricultural zones are thus indicated in the aforementioned figures.

   Knowledge of the lime requirement and the region can enable the usually massive tonnes of lime requirement to be reduced by proper timing of its application [11].

   Amount of Lime per 100kg of soil

   10

   9

   8

   7

   6

   5

   4

   3

   2

   1

   0

   Blank 5ml 15ml 20ml 30ml 40ml 50ml

   Mean pH

   y = 0.052x + 6.348

   R² = 0.951

   8

   7.5

   Akim Qua

   Ediba Anantigha Ikot Efanga Efut Abua

   10

   9.5

   9

   8.5

   pH value

   Fig.1. Mean Lime requirements for acid soils in Calabar Municipality

   Amount of lime per 100kg of soil

   y = 0.057x + 6.71

   R² = 0.975

   y = 0.066x + 6.362 R² = 0.946

   60

   0 10 20 30 40 50

   y = 0.055x + 6.467

   R² = 0.954

   y = 0.045x + 6.468 R² = 0.992

   7

   6.5

   6

   Fig.2. Comparison of Lime Requirement for soils of selected villages in Calabar Municipality

   Amount of Lime per 100kg of soil

   10

   9

   8

   7

   6

   5

   4

   3

   2

   1

   0

   Blank 5ml 15ml 20ml 30ml 40ml 50ml

   Mean pH

   8.5

   8

   7.5

   7

   pH value

   Fig.3. Mean Lime requirements for acid soils in Odukpani Local Government Area

   10

   9.5

   9

   Obon Itiat

   Okoyong Urban Junction Ikot Ekpo

   0

   10

   20

   30

   40

   50

   60

   Amount of lime per 100kg of soil

   y = -0.000×2 + 0.077x + 7.074

   R² = 0.923

   6

   y = -0.000×2 + 0.081x + 6.888

   R² = 0.966

   6.5

   y = -3E-06×2 + 0.052x + 6.635

   R² = 0.937

   y = -0.000×2 + 0.084x + 6.452 R² = 0.952

   y = 0.070x + 6.394

   R² = 0.943

   Fig.4. Comparison of Lime Requirement for soils of selected villages in Odukpani Local Government Area

   Amount of Lime per 100kg of soil

   12

   10

   8

   6

   4

   2

   0

   Blank 5ml 15ml 20ml 30ml 40ml 50ml

   Mean pH

   Fig.5. Mean Lime requirements for acid soils in Akamkpa Local Government Area

   10

   9.5

   9

   8.5

   8

   Adim

   Ibiahe Akpet

   Akamkpa Urban

   7.5

   7

   6.5

   y = -0.001×2 + 0.105x + 7.409

   R² = 0.967

   y = -0.001×2 + 0.100x + 6.743 R² = 0.993

   y = -0.001×2 + 0.100x + 7.448

   R² = 0.949

   y = -0.001×2 + 0.133x + 6.398 R² = 0.955

   6

   0

   10

   20 30 40 50 60

   Amount of lime per 100kg of soil

   pH value

   Fig.6. Comparison of Lime Requirement for soils of selected villages in Akamkpa Local Government Area

   Amount of Lime per 100kg of soil

   10

   9

   8

   7

   6

   5

   4

   3

   2

   1

   0

   Blank 5ml 15ml 20ml 30ml 40ml 50ml

   Mean pH

   Fig.7. Mean Lime requirements for acid soils in Obubra Local Government Area

   10

   9.5

   9

   pH value

   8.5

   8

   7.5

   7

   6.5

   6

   y = -0.001×2 + 0.076x + 7.865 R² = 0.954

   y = -0.001×2 + 0.084x + 7.581 R² = 0.973

   y = -0.001×2 + 0.130x + 6.634 R² = 0.970

   Usumutong Ugep Apiapum Ediba Mkpani

   y = -0.000×2 + 0.104x + 6.612 R² = 0.959

   y = -0.000×2 + 0.064x + 7.508

   R² = 0.983

   0 10 20 30 40 50 60

   Amount of lime per 100kg of soil

   Fig.8. Comparison of Lime Requirement for soils of selected villages in Obubra Local Government Area

   Amount of Lime per 100kg of soil

   10

   9

   8

   7

   6

   5

   4

   3

   2

   1

   0

   Blank 5ml 15ml 20ml 30ml 40ml 50ml

   Mean pH

   Fig.9. Mean Lime requirements for acid soils in Obudu Local Government Area

   10

   9.5

   9

   pH value

   8.5

   8

   7.5

   y = -0.000×2 + 0.072x + 6.952

   Utanga Utugwang Ranch Bendi

   7 R² = 0.987 y = -0.000×2 + 0.058x + 6.798 R² = 0.975

   6.5

   6

   y = -0.000×2 + 0.069x + 6.993 R² = 0.986

   y = 0.033x + 7.191 R² = 0.934

   y = 0.047x + 6.837 R² = 0.990

   0 10 20 30 40 50 60

   Amount of lime per 100kg of soil

   Fig.10. Comparison of Lime Requirement for soils of seleced villages in Obudu Local Government Area

   Amount of Lime per 100kg of soil

   10

   9

   8

   7

   6

   5

   4

   3

   2

   1

   0

   Blank 5ml 15ml 20ml 30ml 40ml 50ml

   Mean pH

   Fig. 11. Mean lime requirements for acid soils in Ogoja Local Government Area

   10

   9.5

   9

   8.5

   8

   Yahe

   Okpoma Okuku

   Ogoja Junctn

   7.5

   7

   y = -0.001×2 + 0.093x + 7.329

   R² = 0.995

   y = -0.000×2 + 0.073x + 7.605

   R² = 0.961

   6.5

   y = -0.001×2 + 0.110x + 7.078

   R² = 0.914

   y = -0.001×2 + 0.090x + 7.297

   R² = 0.985

   6

   0

   10

   Amount of lime per 100kg of soil

   50

   60

   40

   30

   20

   pH value

   Fig.12. Comparison of Lime Requirement for soils of selected villages in Ogoja Local Government Area

4. Discussion and Conclusion

   The pH and Lime requirement for Cross River State soils were investigated and the average values of pH of soils in representative areas of the States Local Government Areas are presented in the Tables 1. There was no distinctively overall State average pH that could have a clear physical meaning, however, average values for LGAs were meaningful. From Table 1, these were in the order:

   Altogether 34 samples were collected all over the State. Each of these 34 samples was made up of 10 sub-samples taken at 1 kilometer apart. These formed the best representative samples of the areas following the approach obtained by Peech [8]. This method was considered to be one of the best taking the accessibility of the areas into consideration.

   Areas of identical geological features, hence having identical top soils which constituted sampling zones, were identified using the geological map of Cross River State. The homogeneity of soil in a given sampling area may be necessary to justify the application of the sampling strategy employed. The sampling areas and points were located on a map for identification and for future references if necessary.

   Results presented on Table 1, and in Figures 1-11 show that most parts of Cross River State soil are only fairly acidic (pH=5.89-6.87); with Calabar LGA having mean pH values of 8.89- 6.78. The clayey soil in the Cross River State may owe their relatively high acidity to the Alumino -silicate that forms the clay (Geological Survey report of Southern

   Nigeria, 1962). The aluminum in the Clay may polarize the water in the soil solution and hence give it acidic character [1].

   Another cause of the acidity of the heavily forested areas may be decay organic matters which may break down to give carboxylic acid phenolic compounds which are acidic in nature. The basic components of the decayed organic matter like NH4+ easily reacts with rain water just as in the case of magnesium and calcium.What is left over is the acidic part which makes the soil acidic [2], [10], [13].

   The results on Lime requirement have been presented in graph (Figures1-12), which show the lime requirement along with the predictive equations (The soils in the Cross River land show low buffer character. The buffer character is the resistance of a soil to change in pH when Lime is applied. It cannot be determined from ordinary measurement of the pH of a soil.

   A soil which appears alkaline may even have a high resistance to lime. However, this tendency of the soil appears generally pronounced in areas where acidity is high. With only a few exceptions in some places like Ikom and Bendi, soil resistance to lime is more marked, otherwise soil resistance tolime is less marked. As shown in the map, slight buffer characteristic occur in Ikom and Obudu. The factor responsible for buffer activity may be the nutrient of the soil concerned. Where high acidity is available due to organic material, a greater amount of Lime will be required to neutralize the acidity. Another factor is Aluminum which

   hydrolyses in the soil and exists as Aluminum hydroxide. This compound is amphoteric. It behaves as an acid in the presence of a base and as a base in the presence of acid. It is therefore capable of neutralizing the effect of lime in the soil, hence a greater amount of lime has to be applied in a very small area in order to reduce the acidity.

   Another factor responsible for the soil resistance to lime is the nature of the subsoil which is the layer of soil below the cultivatable top soil. If the subsoil is acidic it maintains a type of equilibrium with the top soil. Any attempt to neutralize the top soil with lime, the acid from the subsoil is shifted to the soil – hence buffer characteristics is observed.

   The geology of Akamkpa and Obubra may explain the result for the area. The subsoils of these areas are made up of calcium carbonate rocks hence buffer characteristics due to subsoil is not observed. The nature of crops grown in different parts of the Cross River State tends to follow this soil property distribution. In the North East part of the Cross River State where the acidic soil is moderately buffered the Cocoa plants tends to flourish. The presence of large quantity of Cocoa in Ikom and areas of Obudu, especially Bendi and other portions of Bete Clan may be explained by the present result.

   Locality	Average pH	Avg. Lime Req.
   Calabar Local Government Area
   Akim Qua	6.78	0.0523
   Anantigha	6.64	0.0571
   Ikot Effanga	5.71	0.0458
   EfutAbua	5.89	0.066
   Ediba	6.15	0.0552
   Average		6.234
   Spatial Std deviation		0.4645
   CV		7%
   Odukpani Local Government Area
   ObomItiat	6.79	0.0703
   Okoyong	6.71	0.0528
   Odukpani Urban	6.52	0.0575
   Odukpani Junction	6.84	0.0574
   Ikot Ekpo		0.0575
   Average		6.602
   Spatial Std deviation		0.2805
   CV		4%
   Obudu Local Government Area
   Obudu Urban	7.01	0.0478
   Utuquang	7.00	0.0482
   Utanga	7.21	0.039
   Ranch	7.14	0.0434
   Bendi	7.19	0.0338
   Average		7.11
   Spatial Std deviation		0.9925
   CV		1%
   Obubra Local Government Area
   Ugep	6.34	0.0349
   Usumutong	6.93	0.0257
   Apiapum	6.24	0.0589
   Ediba	6.18	0.0605
   Mkpani	6.77	0.0383
   Average		6.492
   Spatial Std deviation		0.3366
   CV		5%
   Ogoja Local Government Area
   Ogoja urban	6.71	0.0317
   Yake	6.77	0.0462
   Okuku	6.59	0.0463
   Okpoma	6.63	0.0379
   Average		6.675
   Spatial Std deviation		0.0806
   CV		1%
   Akampa Local Government Area
   Awi	6.22	0.0587
   Ibiake	6.03	0.0446
   Akpet	6.31	0.0523

   In areas like Ogoja where potential acidity (i.e. acidity determined by Lime requirements as opposed to the active acidity measured directly by the use of pH meter) is comparatively low and the rainfall pattern quite different from that of any other part of the State; and groundnut grows very well [12].

   declined on further increase in pH.Examples are Okuku/Ojala urban, Usumotong/obubra

   Those with convergence- divergenceLMresponse to increasing soil pH indicated the point of 175 ml at pH of 8.2 lime requirement Therefore, there is no rule-of-thumb value for LM , however,it appears that excess LM above is counter-purpose to the solution.

   Table 1: Average pH and lime requirement for soils in local Government areas of Cross River state.

   In terms of acidity, any portion of the State, apart from swamps, is suitable for the cultivation of any species of yam. Yam (D. rotundata) requires a pH not lower than 5.9 [12]. In factyam grows all over the Cross River State. It can be concluded that the soil property is an important index that determines the type of crop to be planted at a particular area. [2].

   Some soils exhibited simple or curved linear increase in limestone requirement (LM) for unit increase in soil pH.Obubra urban is an example. Some paired zones exhibited parallel or contrast lime requirements per increase in soil pH. These included Odukpani junction/ Odukpani urban. Some paired localities with dissimilar pH reached a point of convergence in their lime requirements as their pH changed in opposing direction, thereafter, further lime requirement could only come about by increasing divergence of pH of their soils. Such included Okuku/ Ogoja urban, Yahe/Okpoma, Ediba/ Mkpani and Utugwang/ cattle ranch. Still, others exhibited similarity of lime requirement for increase in. the pH. A fourth set showed convex profile of lime requirement for increase in soil pH i.e. their lime requirement increased in response to increase in pH up to a peak point above which lime requirement

   Akamkpa urban	6.23	0.0587
   Adim	6.87	0.0449
   Average		6.332
   Spatial Std deviation		0.3178
   CV		5%
   Ikom Local Government Area
   Akparabong	6.34	0.036
   Okanga	6.01	0.0361
   Bansara	6.45	0.054
   Abo	5.91	0.0523
   Ikom urban	6.45	0.0388
   Average		6.232
   Spatial Std deviation		0.2548
   CV		4%

   4.1. Recommended Work

   Soil has numerous properties each depending on the other. To have a full understanding of Cross River State soil, other studies like the organic matter content, dissolved ions, organic carbon determination, heavy metals and total phosphorus determinations are very essential complementary exercises that have to be done.

   It is further recommended that samples should be collected in different periods but vary with time [7], [12].

5. Bibliography

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   Delhi, 2003, pp 206 – 249

2. Buckmann, H. O. and Brady, N. C. Nature and properties of soil. Seventh Edition, 1969.

3. DAEA, Lime requirement Cedara College. Available at agriculture. Kznll. gov. Za/Agric Publications/Production Guidelines/PasturesinKwa Zulu Natal/Lime Requirements/Tabid/30, 2005

4. Davis, L. E. 1943, Measurement of pH with glass electrode as affected by soil moisture. Soil Sci. 56:405-

5. FAO., Water quality for agriculture, FAO Irrigation and Drainage Paper, 29: 1, 1994

6. G, Kidder, E. A. Hnason, Jr. Neutralizing excess bicarbonates from irrigation water. University of florida, IFAS Extension service Publication #SL142. Available at http://edis.ifas.ufl.edu/ss165, Accessed December 19, 201

7. L. D. Baver. Factors affecting the hydrogen ion concentration of soil. Soil Science, 1927 23: 399414.

8. M. Peech, Lime requirement, In: Methods of soil analysis Part 2. Monograph No 9 (Editor in Chief: C. A. Black). American Society of Agronomy Inc, Madison Wisconsin, USA. 1965, pp927

9. Mclean E.O. Soil pH and lime requirement methods of soil Analysis. Part 2, 2nd edn, AgronMonogr 9. ASA-CSSA-SSS A, Madison, Wisconsin, 1982, pp.199-224.

10. Panda, N., Sarkar, A. K., Mathur, B. S. Chemical degradation leading to soil acidity and its amelioration. In; Soil management in relation to land degradation and environment (Eds T. D. Biswas and Nara Yanasany) Bulletin No 17, Indian Society of Soil Science, Division of Soil Science and Agricultural Chemistry, Delhi, 1996, pp 82-88

11. Phillips, T. A. Agricultural Note Book Longman, 1976.

12. R. L. Carolus, and R. E. Lucas. Some factors influencing fluctuation in acidity during period of extreme change in moisture content of soil, 1943.

13. S.P. Raychaudhuri. Agricultural potentiality and productivity of acid soils of India under rain-fed condition, 1976.

14. Sawyer, C. N., McCarthy, P. I., Parkin, G.

    F. Chemistry for environmental engineering and science, 5th edn, McGraw-Hill Publishing Company Ltd, New Delhi, India, 2006

15. SMART! Low Soil pH. 2013 Available at http://www.smart- fertilizer.com/articles/soil-ph

16. W. E. Pound, J. R. Street. Lime and the home lawn, Ohio State University Extension, Agronomy Facts AGF-401-95. Available at ohioline.osu.edu/agf- fact/0401.html. Accessed December 19, 2013.