Abstract

This study was conducted to asses Potassium leaching behavior of six (6) selected parent materials in Eastern Nigeria. The soils were formed from Shale, Coastal Plain Sand, Alluvium, Sandstone, Basement Complex and Basalt. A treatment solution containing O, 50, 100, 150 and 200mg/l of K prepared from KCl were added to 20g of soil samples in duplicated cups, the upper cup perforated, mixed thoroughly and allowed to dry. The cups were carefully covered and allowed to incubate for 1, 7, 30, 90 and 180 days, respectively. A total of 180 experimental units were generated and the treatment combinations were fitted into a Randomized Complete Block Design (RCBD), with 6 soil types representing the blocks for each of the incubation periods. The soil samples were kept moist with deionized water at weekly interval throughout the duration of incubation. At the set days, the concentrations of K in the leachate were measured using flame photometry. The K concentrations with days of incubation were plotted against rates of addition. The result shows that the leaching behavior of K in the parent materials varies under similar experimental conditions. Coastal Plain Sand, Sandstone and Basaltic Soil with high sand content exhibits highest amount of leaching compared to shale, alluvium and basement complex with high clay content. A higher K losses with high rates of K addition was observed and K decreased with time (days) of incubation.

Keywords: Potassium, Leaching, behavior, Soils, of Southeast, Nigeria, Parent, materials, Incubation, time, Physical, and, hemical, Properties, soils, Leaching, effect, of, K.

Received: 8 January 2018 / Revised: 16 April 2018 / Accepted: 20 April 2018/ Published: 23 April 2018

Contribution/ Originality

This study uses incubation methodology in assessing leaching potential of different soil types. This study is one of the very few studies which investigated leaching behaviour of soils of southeastern Nigeria. The paper’s primary contribution is the finding that soils with high sand content exhibits high K leaching than others.

1. INTRODUCTION

Potassium is the third major nutrient element after Nitrogen and Phosphorous for crop production, required in large quantity for buildup of biomass. When Potassium is applied in the form of water soluble fertilizer, it can either be absorbed on the clay minerals, taken up by plants or leached out. The extent of each mechanism and component depends upon various factors including the nature of parent materials, soil physical and chemical properties, contact time, amount of K applied, rainfall or irrigation etc (Alfaro et al., 2004; Kolahchi and Jalahi, 2007; Sharma and Sharma K, 2011) . Leaching under field conditions has been regarded as the movement of nutrients from top soil down the profile beyond the root zone and potentially to surface water by lateral movement or lower to underground water (Broschat, 1995; Sharma, 1998). Fertilizers are applied at high rates to increase yield, yet little is known about the leaching potentials of nutrients from soils into the surrounding and underground water.
Barman et al. (2012) reported that soluble element K+ are known to be quickly solubilized in the soil solution, with high quantity lost to leaching, which leads to poor plant growth and quality. Gikonyo et al. (2010) reported that the amount of nutrient leached increase with increasing rates of fertilizer applied and total nutrient concentration in leachate is higher than in soils. The greater P losses to the environment lead to an environmental pollution. Broschat (1995) observed that K+ is associated with harmful algea blooms and eutrophication of lakes and ponds which decrease water quality. Meza et al. (2010) carried out a study to evaluate the effect of different column contact time on the release of inorganic constituents from bottom ash and demolition waste, it was observed that variations in contact time have no significant effect on the release of the selected constituents and leaching parameters at low liquid to solid ratios. Barman et al. (2012) reported that the rate of nutrient leaching decreased overtime and also controlled the release of fertilizers with time. Increasing costs of fertilizers, low yield of crops and concern with water quality have motivated interest to minimize losses due to leaching and to improve the efficiency use of fertilizers. Information on the leaching behavior of potassium in Eastern Nigeria is scanty. The study is therefore aim at evaluating the level of K leaching losses in these soils using column leaching experiments.

2. MATERIALS AND METHODS

2.1. Description of the Study Area and Soil Sampling

Six surface soil samples were used for the study to represent the six (6) dominant soil parent materials in Eastern Nigeria. These include; Odukpani located on latitude 50 71 N and longitude 80 201 E, derived from shale formation with a smectite clay mineralogy and typic hapludult (USDA) soil type, Umudike (Latitude 40 59 N and longitude 70 491E derived from coastal plain sand with kaolinitic clay mineralogy and typic paleudult (USDA) soil classification, Itu lies at coordinate of 50 100 N and 70 591 E form from alluvium deposit, classify as Rhodic tropudults with Kaolintic clay mineralogy Amaeke derived from sand stone, (coordinate 50 331N 70 3E with smedite clay mineralogy classify as typic Tropaquents, Akamkpa with coordinate 50 191 N 80 201E form from Basement complex, with smectite clay, as Typic Tropaquent USDA classification) Ikom (coordinates of 50 571 N80 421 E) form from Basalt dominated by smectile clay with Typic Dystropept (USDA) classification.

The climate is humid tropical with annual rainfall of about 2163 – 3000mm with 1-3 dry months in the year. Mean annual temperature varies between 27 – 280C with relative humidity of 75 – 80% (Okorie, 1987). The figure 1 shows the map of the study location.

Figure-1. Map of Eastern Nigeria showing Sampling Sites

Source: GIS Laboratory, Office of the Akwa State Surveyor General

2.2. Incubation Procedure and Laboratory Analysis

Twenty grams of soil was weighed into a duplicated cup with a capacity of 23cm in dimeter abd 13cm in length and the upper cups perforated (Ayodele and Agboola, 1981). A 20ml portion of the treatment solution containing 0, 50, 100, 150 and 200mg/l prepared from KCl was added to each of the soil in the cups, mixed thoroughly for effective mixing of the K solution with the soils and allowed to dry. The cups were carefully covered and allowed to stand for 1, 7, 30, 90, 180 days respectively. The treatment combinations were then subjected into a Randomized Complete Block Design (RCBD), with 6 replications or blocks. The soils were kept moist with 30ml distilled water at weekly intervals and covered for the duration of incubation. At the set days, the potassium in the leachate was determined using flame photometry.

Parts of the soil samples were air dried, crushed and sieved through 2mm size sieve and used for the following analysis: Particle size distribution was analysed using hydrometer method (Klute, 1996) soil PH was determined in water 1:2.5 soil and water ratio in KCl using glass electrode as described by Udo et al. (2009). Organic matter was determined by wet-oxidation method described by Udo et al. (2009). Available phosphorous was determined by Udo et al. (2009) after extraction by Bray P-I extractant. Exchangeable cations were extracted with neutral NH4OAC. Calcium and Magnesium were determined in the extract by EDTA titration as described by Udo et al. (2009). Potassium and Sodium was determined by the use of flame photometer. Effective cation exchange capacity (ECEC) was obtained by the summation of the exchangeable cations and exchangeable acidity as described by Udo et al. (2009).

3. RESULTS AND DISCUSSION

The physical and chemical properties of selected soils of the study area are shown in Table 1. The particle size analysis showed that the soils were generally light textured and the variation in the texture reflects the differences in the parent materials. This difference in texture will affect water and nutrient leaching and retention as well as suitability of soils as a rooting medium in these soils (Aguilera et al., 2012). The soil pH in water and KCl ranged from 5.0 – 6.1 and 4.4 – 5.9, respectively with a mean of 5.4. These range are generally, considered slightly acidic condition which is considered satisfactory for crop production in this zone. All the pH values in salt extract were less than those in the aqueous extract, indicating that the soils were negatively charged at their natural state (Villapando and Graetz, 2001). The soils were non-saline with low electrical conductivity values (Table 1), indicating that the soils are salt free. Organic matter contents of the soils were above the critical level of (2gkg-1) proposed by Aduayi et al. (2002) for soils of Eastern Nigeria. Total N were below the critical level (2gkg-1) and P level lower than the critical level of 12-15mgkg-1 except sandstone soils (Aduayi et al., 2002). The order of abundance of exchangeable base for the soils was Ca>Mg>K>Na. The effective cation exchange capacity (ECEC) was low except in Basaltic soil with critical level of 12 cmolkg-1. The low ECEC values are indication of the presence of low activity clays. The base saturation values were high in the soils, except in soil derived from Basement Complex with moderate level of 47.1cmolkg-1 (Enwezor et al., 1989). This result agreed with the findings of Halrvin and Beaton (2006) which stated that the release of nutrients by soils is influenced by the cations.

Table-1. Physico- chemical properties of the soils

EC – Electrical Conductivity, OM – Organic Matter, AV.P- Available Phosphorous, EA-Exchangeable Acidity, ECEC – Effective cation Exchange Capacity, SL – Sandy Loam, SCL – Sandy Clay Loam, SC – Sandy Clay

3.1. The Leaching Behavior of Potassium (K) in Soils

The leaching rate of applied K in the soils of the study area was obtained from the relationship between K extracted from the leachate at different rate of applied K and at different incubation periods and are presented in Figures below, the letters A to E denote the (contact time) days of incubation as A – 1, B – 7, C – 30, D – 90 and E – 180 days. The graphs are plots of the concentration of K in leachate and amount or rates of K added.

Figure-2. Plot of K concentration in leachate VS rates of K added (cmolkg-1) in shale parent material (Odukpani)