Soil Texture Under Banana and Maize Land

Introduction
Water is one of the most important factors limiting the growth of plants in all Agricultural systems. In this respect, good water management is necessary in order to solve water related problems such as irrigation and erosion control. Infiltration is the process by which water arriving at the soil surface enters the soil.
This process affects surface runoff, soil erosion, and groundwater recharge (Gregory et al. , 2005). The rate at which it occurs is known as infiltration rate which mainly depends on the characteristics of the soil. ( Saxton, 1986) reported that, the major soil and water characteristics affecting infiltration rates are: the initial moisture content, condition of the surface, hydraulic conductivity of the soil profile, texture, porosity, degree of swelling of soil colloids, organic matter, vegetative cover and duration of irrigation or rainfall and of these, soil texture is predominant.

Therefore the measurement of water infiltration into the soil is an important indication in regard to the efficiency of irrigation and drainage, optimizing the availability of water for plants, improving the yield of crops, minimizing erosion and describing the soil permeability. Land use and land cover changes among other factors have also been reported to infuluence the infiltration rate of soil. According to (Suresh, 2008), for a given soil, the land use pattern plays a vital role in determining its infiltration characteristics.
Different land use practices affect infiltration rates in different ways. (Taylor et al, 2009), observed that intensified land use results primarily in a change in soil structure rather than soil compaction. When land is put to certain uses, there is an accompanying change in the properties of the soil and this alters the hydrological balance of the soil. According to (Osuji, 2010) infiltration rates in tropical forests under bush fallow were found to be high compared to arable crop land. In addition, Majaliwa et al. 2010) explains that the change from natural forest cover to tea and Eucalyptus induces changes in top soil properties like exchangeable Magnesium and Calcium, available Phosphorus, soil organic matter, soil pH, and soil structure of sub soil. Furthermore, Land use/type cover influences soil organic matter evolution which is a vital indicator of soil quality and it has implications on soil properties like aggregate stability/soil structure, infiltration and aeration rates, microbial activity and nutrient release (Boye and Albrect, 2001).
Additionally a soil’s water retention characteristic, is affected by soil organic matter (SOM) content and porosity, which are significantly influenced by land use type (Zhou et al. , 2008). Gatundu catchment is one of the catchments in Kenya which have experienced soil degradation due to conversion of natural forest to crop land mainly banana, maize and Coffee. This has been fastened by the increasing population in the catchment leaving most of the natural forest cover cleared and replaced by crop land.
The result has been massive soil degradation, through loss of plant nutrients and organic matter, soil erosion, river bank degradation; build up of salinity, and damage to soil structure (Bekunda et al. , 2010). Therefore this study aims to determine the degree of relationship between infiltration rates and the land use types in two selected sites under Banana and Maize cropping systems in Gatundu sub catchment.
Significance of the study
The knowledge of water retention capacity and land use effects is important for efficient soil and water management.
Upon conversion of natural lands to cultivated fields, water retention capacity is strongly influenced (Schwartz et al. , 2000; Bormann and Klaassen, 2008; Zhou et al. , 2008). Thus, infiltration rate is an important factor in sustainable agriculture, effective watershed management, surface runoff, and retaining water and soil resources. Properly designed and constructed infiltration facilities can be one of the most effective flow control (and water quality treatment) storm water control practices, and should be encouraged where conditions are appropriate (Ecology, 2005)
Objectives
The objective of the study is to determine the effect of banana and Maize land use practices on water infiltration into the soil in Gatundu catchment
Specific Objectives
Describe how different soil types influence water flow through the soil Compare Water movements through the soil at two different sites (Banana and Maize fields) To find out how soil texture influences water infiltration into the soil.
Methods And Materials
Introduction
This section covers the methods and materials used in the study which include description of the study area, experimental design, field data collection procedures for soil samples and data analysis procedures; laboratory and statistical data analysis using Microsoft office package.
Study area
Gatundu district is one of the districts located in central province of Kenya at 1° 1′ 0″ South, 36° 56′ 0″ East; covering an area of 481. 1 km2 and borders Thika district to the East and North and Kiambu East to the South and West .
The population density varies from 370 persons per Km2 in Chania and Mangu divisions to 636 persons per Km2 in Gatundu division on the 2008 population projections. Gatundu division is the most densely populated division with 636 persons per square Km. The population over the plan period is expected to increase marginally thereby increasing demand and competition for the available resources like water and land resources (Gatundu District Development plan, 2008 -2012). 3 ` Figure 5: Map of Gatundu south Topography features of Gatundu district Gatundu district is located about 1520 m ASL at the lowest point and 2280 m ASL at the highest point.
There are several permanent rivers and streams that traverse the landscape and these include Ndaruga, Thiririka, and Kahuga. All these rivers flow from the Aberdare ranges to the west and towards the southeast joining River Tana thus forming part of Tana and Athi river 4 drainage system. The train is conducive for gravity system of irrigation (Gatundu District Development plan, 2008 -2012). Terrain Gatundu district is characterized by a ragged terrain, which has had both the negative and positive impacts on the development of the district.
The steep slopes and valleys characteristic of the most part of the district, coupled with intensive crop cultivation render most of these areas susceptible to soil erosion making it necessary for farmers to practice terracing which is costly. The conducive environment in the district favour the cultivation of tea and coffee however, other crops like cereals, horticultural crops such as pineapple, mangoes, avocadoes and vegetables plus bananas (Gatundu District Development plan, 2008 -2012). Soils Gatundu district has soils that correspond entirely with typical Aberdare Humic Andosols and Nitosols.
These Nitosols have great agricultural potential coupled with the relatively high rainfall regime in the region. Production of tea, coffee, tropical fruits and food crops such as maize, beans and potatoes are the most common sources of income to the households. The hilly terrain of the district has had profound effect on the soils, resulting into low and moderate fertility levels (Gatundu District Development plan, 2008 -2012). Climate The rainfall pattern is bi-modal with two distinct rainy seasons, long rains falling in March and May while short rains between October and November.
The amount received varies with altitude ranging from 800 mm to 2000 mm with the highest rainfall being experienced in the tea zones. The mean temperature is 200 C with coldest months being June, July and August. The hottest months are February, March and April. Temperatures vary from 80C minimum to 300 C maximum during the year. (Gatundu District Development plan, 2008 -2012)
Research design
A completely randomized block design was used for the study. Two treatments were considered (Banana and Maize land uses) and the blocking was landscape position. For Each land use type, only one experiment was carried out because of time. .
Data collection procedures and laboratory analysis
Soil Texture
Five (5) soil samples from both Banana and Maize land uses at different landscape positions were collected. The sampling was done at depth of 0 -15 cm and were collected using a 50 mm diameter auger using a Random sampling Technique as explained by Haghighi et al. (2010). The 0-15cm depth was considered because it’s the major agricultural layer and root zone for most of the crops. The five soil samples from each land use were thoroughly mixed to obtain composite soil samples which were taken to Makerere University Laboratory for Analysis.
Soil texture was determined using the hydrometer method described by Bouyoucos (1962) and results presented in percentages of mineral proportions. The samples were passed through an electric shaker for 30 minutes and then the sample was treated with sodium hexametaphosphate to complex Ca++, Al3+, Fe3+, and other cations that bind clay and silt particles into aggregates. The density of the soil suspension was determined with a hydrometer which was calibrated to read in grams of solids per liter after the sand settled out and again after the silt settled. Corrections were made for the density and temperature of the dispersing solutions.
The percentages of mineral fractions were calculated as below; Percent clay: % clay = corrected hydrometer reading at 6 hrs, 52 min. x 100/ wt. of sample Percent silt: % silt = corrected hydrometer reading at 40 sec. x 100/ wt. of sample – % clay Percent sand: 6 % sand = 100% – % silt – % clay Results were reported as percentages of the mineral fraction, % sand, % silt, and % clay. Soil texture was based on the USDA textural triangle.
Infiltration
The infiltration rate was determined using double-ring infiltrometer as described by American Society for Testing and Materials (1994).
It consists of two concentric metal rings. The rings were driven into the ground and filled with water. The outer ring helped to prevent divergent flow. The drop-in water level or volume in the inner ring was used to calculate the infiltration rate. Clock time was recorded when the test began and noted the water level on the ruler at different time intervals as seen in Appendix 1, recorded the drop in water level in the inner ring on the ruler and kept adding water to bring the level back to approximately the original level.
The tests were conducted for a period of one to two hours, until the infiltration rate became constant. The infiltration rate was calculated from the rate of fall of the water level in the inner ring as seen in Appendix 1 in the tenth minutes in both the banana field and maize fields. The data was analyzed by drawing graphs of infiltration rate and cumulative infiltration. In both cases, curves were obtained. Plate 1: Infiltration in Banana and Maize field respectively
Results And Discussions
Soil Infiltration Measurements
Soil infiltration measurements were made at 2 sites in Gatundu sub catchment (Plate 1 above). The two sites have the same soil characteristics, therefore they have been classified by the different land uses and land scape positions coupled by other field observations. Sites were selected based on land use, proximity to water source, site accessibility, and soil type. Table 1: Description of infiltration sites Site Location Banana Site Observed and use and field observations Site with Banana plantations, Has some mounds, some trees adjacent to the field, it’s on a higher elevation Maize Site Site with Maize, The site is close to a trench used for moving water, Its close to the road , It’s on a lower elevation Figure 1(Banana land use) and Figure 3(Maize land use) shows that the water infiltrates at a very high rate at the beginning with 1800 mm/hr and 720mm/hr respectively; because the hydraulic gradient is high and then keeps declining with time until it becomes fairly steady after the soils become saturated, which is termed as basic infiltration rate.
This is also emphasized by Horton (1940) where he asserts that infiltration becomes constant with time as the soil column reaches fully saturated conditions which occurred at 40th and 49th minute time intervals in Banana and Maize Land use Systems as seen in appendix 1. Rubin and Steinhardt (1963) also showed that the final infiltration rate reached under these conditions is equal to the vertical hydraulic conductivity of a saturated soil. 8 The steady state in Maize was attained earlier than in banana land use corresponding to 204mm/hr and 450mm/hr respectively.
This can be associated to soil disturbances during ploughing and land preparation season after season for annual crops like maize compared to banana field (Perennial) which have less soil disturbances. The scenario under maize land use may lead to soil compaction as a result of continuous cultivation. This is emphasized by Pitt et al. , 2002 and 2008; Pitt et al. , (1999b) who found substantial reductions in infiltration rates due to soil compaction. The implication is that beyond the steady point (saturation point), if more water is applied to the soil, it results into surface water runoff.
Infiltration depends upon physical and hydraulic properties of the soil moisture content, previous wetting history, structural changes in the layers and air entrapment. The basic infiltration rate of maize land use is lower than that of Banana land use system as seen in Appendix 1; this can be associated to a number of factors although not conclusive for the attained results;

The Initial moisture content; the study was carried out in a rainy season, therefore for saturated soils, the infiltration falls to the aturated hydraulic conductivity almost instantaneously.
Considering the type of land use in each of the sites; Soils under Perennials (Banana Land use) are subjected to less interferences in terms of land preparations compared to land under annuals (Maize Land use) which correlates with the obtained results of 450mm/hr and 204mm/hr respectively.
The surrounding of the site; the Maize field is on a lower elevation and near a trench which collects water, therefore it’s possible that the soils could easily reach saturation.

In each set of measurements, the infiltration rate of the Banana field belonging to the sandy clay loam was much higher than Maize field belonging to clay loam because of the variation in the physical properties of the two textural classes. In the banana field, basic infiltration rate was attained at 450mm/hr which is higher than that of maize field, 204mm/hr and this explains the relationship between soil texture, structure and infiltration which was obtained in our results where the Banana field with sandy clay loams having larger pores allowed in more water to infiltrate compared to clay loam with relatively smaller pores.
From our results, The banana field reached saturation earlier (40th minute) than the Maize field (49th minute) which deviates from the assumption that the field at lower elevation reaches saturation earlier than the other on the higher elevation, and this case the maize field was on a lower elevation. As it is not possible to vary soil texture independently of other characteristics it is not inferred that the infiltration rates are caused by texture.
Conclusion And Recommendation
Generally from the findings, the two sites registered high basic infiltration rates with banana and maize land use having 405mm/hr and 204mm/hr respectively. The two sites as well reached saturation easily because of the amount of water that was held within the soil because of the rainy season.
Several factors influenced the test; measuring rapidly changing water levels was difficult especially for one minute time intervals and therefore subject to inaccuracy and the local site features, challenges in elevation and the soils being too soft which kept altering the position of the ruler and varying the depth thus may have affected individual test results. Therefore the study required more data collection and time to be able to sample many sites at different time intervals. For this study, tests were conducted during a rainy period in December, 2012, where the water table was expected to be above most soil layers.
However, Infiltration is a key parameter in Watershed management therefore Properly designed and constructed infiltration facilities can be one of the most effective flow control (and water quality treatment) , and should be encouraged where conditions are appropriate (Ecology, 2005). Additionally infiltration separates water into two major components surface runoff and subsurface recharge, therefore assessment and Evaluation of runoff risk has assumed an increased importance because of concerns about associated pollution hazards in which pollutants are likely to be transferred from soil to rivers and lakes.
The speed of irrigation of fields is based on infiltration tests and data; in surface irrigation, infiltration changes dramatically throughout the irrigation season. The water movements alter the surface structure and geometry which in turn affect infiltration rates; therefore accurate determination of infiltration rates is essential for reliable prediction of surface runoff. As environmental impact assessments are concerned with long-term effects, it is essential that the 13 infiltration data on which they are based should be reasonably stable. For planning purposes it is essential to know the stability of infiltration data.
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