Effects of ploughing depth variations on maize ( Zea mays ) growth: a study at Nyankpala in the Northern Region of Ghana

This study evaluated the effect of different ploughing depths on maize ( Zea mays ) growth at Nyankpala in the Northern Region of Ghana. Plant height, leaf count, and stem girth were measured at no-plough (NT), 10-20 cm (PD 20 ), and 20-30 cm (PD 30 ) depths. Soil bulk density and texture were also determined for NT, PD 20 , and PD 30 . Plant data were evaluated using one-way analysis of variance in GENSTAT statistical program, and the means were separated with the least significant difference (LSD) at p<0.05. The results revealed significant differences between the various depths of ploughing, with the best maize growth characteristics recorded under PD 30 , followed by PD 20 and finally, NT. The PD 30 had nitrogen, phosphorus and potassium (NPK) contents of 0.24 %, 6.08 mg/kg, and 58 mg/kg, respectively, followed by NT with NPK contents of 0.13 %, 5.23 mg/kg, and 46 mg/kg, respectively. The bulk density of the soil decreased with increasing ploughing depth. From the results, the study recommends a plough depth of about 20-30 cm for maize production in the study area and other regions with similar physical soil properties and agronomic practises.


Introduction
Tillage is an important management step in crop production as it has a substantial impact on the soil, crop growth, and yield.It has been an essential part of agricultural technological advancement, particularly in food production (Zewditu et al., 2020).Tillage techniques help to control weeds, create an appropriate seedbed for crop plants, add crop residues to the soil, loosen the soil, boost chemical reactions, and enhance the physicochemical state of the soil, all of which help crop plants grow and develop (Wasaya et al., 2019).Tillage procedures have a significant influence on soil physical qualities.Productive farming needs a variety of tillage practises that improve the soil's physicochemical properties and microbiological activity for agricultural crop growth (Hazarika et al., 2018;Ramadhan, 2021).Tillage systems provide an optimal seedbed for plant growth (Aikins and Afuakwa, 2012;Khan et al., 2020).The process of turning and loosening the soil regulates soil nutrients that are important for optimum crop yield.As a result, the depth of till affects root growth, accumulated nutrients, and yield (Cai et al., 2014).Selecting tillage strategies that improve soil physical qualities is critical not just for increasing yields (Hazarika et al., 2018), but also for reducing agriculture's environmental effect whilst fostering sustainability (Botha, 2013).
Tillage has a range of benefits as well as adverse physical, chemical, and biological impacts on the soil and crops, based on the techniques employed.Negative effects on soil characteristics and crop yield result from excessive or improper tillage techniques.Disturbing the soil may also significantly alter fertility status, with results ranging from favourable to poor crop production (Yaroson et al., 2019).Tillage affects the physical characteristics of the soil, including its organic matter content, aggregation, porosity, bulk density, and moisture content.Proper tillage causes desirable physical changes in the soil environment, which ultimately translates to increased crop yields (Hazarika et al., 2018).Physical factors that directly affect soil productivity and sustainability include aggregate stability, water and soil conservation, and infiltration capacity.On an annual basis, the best tillage technique for a field or farm will vary depending on soil type and weather conditions.Effective tillage procedures give the optimum planting environment for plant emergence, growth and unlimited root extension (Abagandura et al., 2017).
Conventional and conservation tillage systems are the methods that have been established, regardless of the equipment utilized.An effective soil conservation system protects soil from wind and water erosion, maintains a healthy seedbed, eliminates compacted layers, and supports the development of organic substances (Aikins et al., 2012;Hydbom, 2017).With conservation tillage such as no-till, soil physical characteristics are typically better due to improved saturated and unsaturated hydraulic conductivity than conventional tillage systems due to the continuity of pores (Busari et al., 2015).Further advantages include protection of the soil against erosion, preservation of soil and water, cost and time savings, and increases in soil fertility (Sharma and Abrol, 2012).However, other researchers (Schneider et al., 2017;Wang et al., 2022;Schneider et al., 2017;Wang et al., 2022) found conventional tillage practises to improve the accessibility of subsoil nutrients to the plant, which increases its yield.Conventional tillage can disrupt soil layers, allowing roots to penetrate deeper and gain access to additional resources stored in the subsoil.It could facilitate subsoil water uptake and hence stabilise the yield of crops.According to Usharani et al. (2019), well-tilled soil promotes rainfall infiltration, reducing runoff and allowing for the storage of moisture for subsequent use by the crop.It also encourages good root formation and development.Deep ploughing is a treatment for undesirable soil compaction that improves crop growth conditions.Mechanical disturbance of the subsoil increases the water-holding ability and lowers its resistance to root penetration (Cai et al., 2014).In the different conventional tillage methods, energy plays a key role.As the depth of tillage increases, so does the amount of energy consumed and the wear and strain on the implement and power source.
In agriculture, the depth of ploughing has been of particular relevance since it may influence soil decomposition rates (Baker, 2016).However, such tillage necessitates a huge amount of energy investment and comes at a significant expense to farmers.Variable-depth deep ploughing applied on a location basis has proven effective in reducing undesirable soil compaction in locations where it occurs while avoiding the use of this costly process (Błażewicz-Woźniak et al., 2015).
Good crop establishment is essential for high yields.However, many crops require different soil physical characteristics to establish successfully.High bulk density and soil resistance can have an adverse impact on root development and growth, causing root action and features to change to accommodate increasing strength.Ploughing practises can have a significant influence on various soil layers, affecting both strength and porosity, which can limit root development (Botha, 2013).The relationship between soil physical properties and plant root systems is essential in this process since both are directly connected to proper tillage practises (Qamar et al., 2015).Soil is an important natural source and has an economic and eco-social capability for improving plant growth, quality, and yield (Usharani et al., 2019).Choosing the right tillage system for a particular soil type requires careful consideration of the soil type (Wasaya et al., 2019).When soil is in good condition, root systems develop well, which is necessary for optimum root growth and maximum crop yields (Aikins et al., 2012).
For the past decade, farmers have continued to record a low growth rate and yield of maize (Adzawla et al., 2021;Kanton et al., 2016).Although they sow improved and certified seeds, this does not produce a significant difference in the growth rate and yield of maize.This is most often linked to the monoculture agricultural practise, where farmers continuously till the soil to the same depth each season, depleting its nutrients beyond that depth.According to Cai et al. (2014), due to several years of overexploitation of the topsoil and inappropriate mechanical manipulation, the useful topsoil depth could gradually decline and the plough pan thickens which can potentially affect root penetration.Also, many farmers carry out tillage operations without considering the impact on soil physical characteristics and crop growth (Ozpinar and Isik, 2004;Yaroson et al., 2019).The impact of ploughing depth on crop productivity as well as soil physical properties is important.In the Tolon District and many other parts of Ghana, not much research has been done on the effects of ploughing depth on crop growth and soil properties.Varying the depth of the plough can uncover leached minerals and restructure the soil to make it more conducive for the growth of crops.While different studies propose different optimal ploughing depths for different soils and crops (Abagandura et al., 2017;Aikins et al., 2012;Zhang et al., 2018;Zikeli et al., 2013), there is still no consensus on the best ploughing depth for maximizing crop yields and preserving soil health.This may be due to the complex interactions between soil type, crop type, and other factors such as climate and agronomic management practises (Bonfante et al., 2019;Wasaya et al., 2019).The main objective of this study was to investigate the effects of ploughing depth variation on maize growth.

Description of the experimental site
The study was conducted at Nyankpala in the Northern Region of Ghana.The study area is situated within the Tolon District, which is bordered to the north, east, west, and south by Kumbungu, Sagnarigu, North Gonja and Central Gonja Districts respectively.It is situated between latitudes 9° 15′ and 10° 02′ north, and longitudes 0° 53′ and 1° 25′ west.
Crop farming is the major agricultural activity in the district, with about 90 % of the population involved in crop production such as maize, rice, yams, groundnut and livestock.The climate is characterized by a unimodal rainy season spanning from April -October with minimum rainfall at the end of April to its maximum in July and August.The production of primary crops such as maize is capped at one cropping season due to the rainfall pattern.The dry season in the district lasts from November to April.The average annual precipitation varies from 950 mm to 1200 mm.Except for the lowlands with alluvial deposits, the soil is primarily of the sandy-loam type.Because of the composition of the soil, the area is extremely susceptible to erosion (Ahmed and Anang, 2019;Ghana Statistical Service, 2014).Figure 1

Experimental design
A completely randomized design (CRD) with three replicates on 5 m x 4 m plot each was adopted for this experiment.The field experimental design consisted of three ploughing depths.The treatments were the ploughing depth at 0 cm (no-plough), 10-20 cm and 20-30 cm levels designated as NT, PD 20 and PD 30 , respectively.This gave a total of nine experimental plots spaced at 2 m between rows and 1 m between columns.The spacing was necessary to clearly distinguish plots and to serve as walkways.

Land preparation and planting
The ploughing depth variations were achieved using the disc plough.Ploughing was done using a 3-bottom disc plough with a disc diameter of about 66 cm hitched to an 85-hp Massey Ferguson MF 385 tractor.The desired depth was achieved by careful control of the hydraulic system by the operator and the addition of weights to the plough beam to attain penetrations beyond 20cm.The soil was wet enough after a rainfall for easy penetration of the plough for all the treatments.The initial soil moisture content of the field was determined using the oven drying method (Susha Lekshmi et al., 2014) to be 17.32 % at the time of ploughing.Wang-Dataa maize variety, one of the recommended maize varieties for northern Ghana with a maturity period of 3 months (Adu et al., 2014;APNI and CSIR-SARI, 2022) was chosen for the study.A planting depth of 5 cm was adopted throughout the experiment.The interrow and intra-row planting distances were 80 cm and 25 cm, respectively, with three seeds per hole, which were later thinned to two, after 10 days of germination.There were eight rows in a plot.The plants started emerging on the fourth day and by the 12 th day, almost all had germinated.

Data collection Determination of soil physical properties
Soil dry bulk density was determined for NT, PD 20 and PD 30 treatments.At each treatment, three soil samples were collected and analysed.To determine dry bulk density, a core sampler with dimensions of 5 cm length and 5 cm diameter was used.The samples collected were dried for 24 hours at a temperature of 105 o C (de Oliveira et al., 2015;DeAngelis, 2007;Pappoe et al., 2009).The bulk density was determined using Equation (1).
The soil texture was analysed using the hydrometer method (Huluka and Miller, 2014) and the textural class obtained from soil texture triangle.Sodium hexametaphosphate, Na(PO 3 ) 6 and deionized water were used as reagents.

Determination of soil chemical properties
The analysis of soil chemical properties was carried out at the soil laboratory of the Savannah Agricultural Research Institute (SARI) in Nyankpala.Three sets of soil samples were taken from each treatment (NT, PD 20 , and PD 30 ), dried, sieved in a 2 mm diameter sieve and analysed for their chemical properties.This was done to determine the proportions of soil nutrients in each depth of plough.The chemical properties investigated included total nitrogen (N), available phosphorus (P), available potassium (K), and soil pH.
In the laboratory, the procedure for determining soil N involved the digestion of a sieved (< 2mm) air-dried soil sample in concentrated H 2 SO 4 , the Kjeldahl distillation of the NH 3 formed and quantifying the N by titration (FAO, 2021a).The available soil P test was conducted using Bray P1 method (Boem et al., 2011;Ebeling et al., 2006;Lumbanraja et al., 2017;Mallarino, 1995) with the extractant being NH 4 F solution and dilute HCl.
In determining the available soil K, the exchangeable cation K + method (McLean and Watson, 1985;Moody and Bell, 2006) was used.The reagents used were ammonium acetate and distilled water.The pH of the soil was determined using the electrometric method (Adamchuk and Mulliken, 2005;FAO, 2021b).

Crop parameters measured
The germinated Wang-Dataa maize plants were randomly tagged per plot to monitor and determine the plant height, stem girth, and number of leaves per plant in two-week intervals for eight weeks, beginning two weeks after planting.The germination rate was 80 -85 % due to the activities of field rodents.Thirty (30) plants were tagged in each of the nine plots, given a total of 270 plants.A metre rule was used to determine plant height.The girth of the stem was measured using a thread and a ruler.At two-week intervals, the leaves of the tagged plants per plot were counted.The average of the parameters recorded for each treatment was determined.

Data analysis
Analysis of variance (ANOVA) of the data gathered for this study was done using the GENSTAT statistical program (Payne, 2009), and the means separated using the least significant difference at a 5 % probability level.The results were presented in tables and graphs.

Soil chemical and physical properties Soil pH and NPK content
Nitrogen, phosphorus and potassium (NPK) levels as shown in Table 1 were found to be highest in the 20 -30 cm (PD 30 ) ploughed depth, followed by the 10 -20 cm (PD 20 ) and the NT having the least nutrient content.This could be attributed to leaching of nutrients from the top surface to that depth over time.It might have well been due to the vulnerability of the topmost layer to agents of erosion, which have depleted the nutrient content.Compared to NT, total N accumulation under the other treatments increased by 30.8 -84.6 %, whereas avail-  1).A similar trend was observed by Cai et al. (2014), where N, P and K increased with depths ranging from 0 -80 cm.If nutrients are growth-limiting, tillage enhances the availability of subsurface nutrients to plants, which boosts crop production (Schneider et al., 2017).This is, however contrary to the observation by Zikeli et al. (2013) that nutrient content such as available P, K and soil organic carbon decrease with soil depth in the sample depth from 0 cm to 20 cm.The soil pH decreased with increasing depth, though all were within the range of 5.28 and 5.79.The soil pH of PD 20 and PD 30 was strongly acidic whereas the NT was slightly acidic.A soil pH of 5.1-5.5 is strongly acidic and 5.6 -6.0 is moderately or slightly acidic (Kicińska et al., 2022;Odutola Oshunsanya, 2019).The mineral composition of the parent soil material and the weathering processes that parent material has gone through have an impact on the pH of the soil.In wet environments, soil acidity occurs because of the products of weathering that are leached by water moving laterally or downward through the soil.Tillage had an effect on the soil total N, available P, K and pH.

Soil texture
The particle size analysis results showed that the textural class of the field is sandy loam with little variation in particle composition.The proportions of sand in the soil samples were high, with 71.6 %, 68.2 % and 67.2 % recorded at NT, PD 20 and PD 30 , respectively whereas silt content was 26 %, 25 %, and 22 % for NT, PD 20 and PD 30 respectively.Clay content was 2.4 %, 7.4 % and 10.4 % for NT, PD 20 and PD 30 , respectively.The results indicated a generally high sand content and a very low clay content (Table 1).These soils drain easily and as a result, are vulnerable to the leaching of nutrients from the soil surface to the PD 30 .

Bulk density
The soil bulk density values for the two ploughing depths (PD 20 and PD 30 ) were lower than the NT within the various ploughing depths (Figure 2).The ploughed treatments loosened the soil, resulting in a lower soil bulk density than the NT.Ploughing therefore affected the soil bulk density with respect to the depth of tillage and had an impact on the growth of the crop as a result of easy root penetration and high nutrient absorption rate.According to Stirzaker et al., (1996), plants respond to variations in bulk density by growing the fastest at an intermediate density or lower.Bulk density often characterises the state of soil compactness in response to land use and soil management activities (Indoria et al., 2020).A high soil bulk density negatively affects soil physical properties, and therefore can limit microbial activity and biochemical processes, which are crucial for nutrient availability (Hazarika et al., 2018;Ramadhan, 2021;Yaroson et al., 2019).An increasing bulk density implies a decrease of macropores and an increase in meso-and micropores and the resultant changes impact hydraulic conductivity (Indoria et al., 2020).It also has an effect on soil aeration, which influences water and nutrient uptake.The results are similar to findings by Alamouti and Navabzadeh (2007) that mean soil bulk density decreases with increasing depth.Deep tillage is necessary to decrease the initial bulk density and penetrometer resistance of the soil profile (Baumhardt and Jones, 2005) resulting from continuous and several years of practising soil management at only a particular depth.

Growth characteristics The height of maize plants
The ANOVA of the maize plants' height is shown in Table 2.The plant height was significantly different (P<0.05)among the different ploughing depths except on the 8 th week after planting.The plants' height for the PD 30 depth was significantly higher than the other two treatments.Although there was no significant difference in height between NT and PD 20 at two weeks after planting (2WAP) and 4WAP, there was a significant difference at 6WAP and 8WAP.
Maize plants in the NT and PD 20 were similar in height but substantially (P<0.05)lower than the plants in the PD 30 .The PD 30 treatment produced the tallest plants, which were also significantly (P< 0.05) taller than plants in PD 20 plots.The NT and PD 20 treatments had poor growth characteristics, which could be attributed to high bulk density and low NPK.High bulk density indicates limited soil porosity and high compaction, which lead to restricted plant development and general maintenance.
According to Sharma and Abrol (2012), the loss of root penetration depth induced by high bulk density soils can reduce plant height significantly when compared to plants growing in

Number of maize leaves
Table 3 presents the number of leaves at 2WAP, 4WAP, 6WAP and 8WAP.The number of maize leaves was not significantly (p <0.05) different among the treatments except at 6WAP, with PD 30 being higher than the other treatments, followed by PD 20 and then NT.Maximum leaves in the PD 30 plot could be attributed to the mutual relationship that exists between the bulk density (Figure 2) and roots penetration and the available nutrients (Table 1) at that depth which fix nitrogen into the roots of the maize, thus increasing the growth of leaves.A study by Abagandura et al. (2017) showed that the number of maize leaves in a conventional tillage practise was significantly higher and lower in zero tillage practise.Similarly, Aikins et al. (2012) observed that, no tillage plots recorded the least number of maize leaves, significantly less than other tillage practises.

Stem girth
Table 4 illustrates the impacts on the stem girth throughout the first eight weeks of the experiment from the various ploughing depths.There was no significant change in the plant stem girth between NT and PD 20 , but statistical analysis of the data indicated there was a difference in PD 30 .
There was no significant difference between NT and PD 20 at all the weeks after planting.However, there were significant differences between the PD 30 and other two (NT and PD 20 ) treatments.This might be due to the low bulk density in the NT which allows for a high rate of water absorption, nutrient uptake and easy root penetration.The increase in the stem diameter could also be a result of the high NPK content recorded at that depth of the soil.In a study by Aikins et al. (2012), notillage plots had the smallest stem girth, smallest plant, and fewest leaves per plant among other features.Maize growth characteristics such as plant height and stem girth are influenced by soil fertility management practises (Kanton et al., 2016).

Conclusions
Differences in soil bulk density were caused by variations in tillage depth.No-ploughed depth had the highest bulk density and therefore recorded the least maize growth characteristics, followed by the 10 -20 cm ploughing depth.The ploughing depth of 20 -30 cm had lower soil bulk density and highest NPK content.In general, the number of leaves, height of plants, and stem girth were similar at no-plough and 10 -20 cm ploughing depths The ploughed depth of 20 -30 cm improved the maize growth characteristics measured in this experiment.
Thus, it can be stated that ploughing at a depth of 20 -30 cm is required for maize to have better growth characteristics which could lead to higher yields.This is vital information for farmers on the optimal tillage practise required for maize cultivation.Further research should focus on long term studies on the effects of ploughing depth variations on maize growth and yield, as well as economically evaluating the costs of varying the plough depth.
is a map of Tolon district showing Nyankpala.

Figure 1
Figure 1 Map of Tolon district showing Nyankpala

Figure 2
Figure 2 Bulk densities of the soil at various ploughing depths

Table 1
Chemical and textural analysis of soil at various ploughed depths NT = no-plough , PD 20 =10-20 cm, PD 30 = 20-30 cm In research to compare the plant density and crop production of various tillage regimes,Kisić et al.  (2010)observed that no-tillage treatment had significantly lower maize plant height and thickness, ear size, and kernel count per ear than the other treatments which this study confirms.

Table 3
Effects of different ploughing depths on the number of leaves of maize = No-plough, PD 20 = 10-20 cm, PD 30 = 20-30 cm, WAP = weeks after planting, NS = Not significant NT