Declining soil fertility and climate variability

Declining soil fertility and climate variability are the major constraints to food security. It has led to the implementation of assorted soil fertility management practices to increase agricultural productivity to meet the growing population demands. However, there is limited knowledge on both the economic and environmental sustainability of these practices. Therefore, the study seeks to assess the economic and environmental sustainability of soil fertility management practices. The study will be carried out at Kangutu primary school in the central highlands of Kenya. It will be superimposed on an on-going long term field experiment arranged in split-plot and laid out in a randomized complete block design. The treatments are a combination of two tillage methods and six soil fertility inputs and control. The tillage methods are minimum and conventional tillage. The inputs are: sole mineral fertilizer, crop residues + mineral fertilizer, crop residues + mineral fertilizer + animal manure, crop residues +Tithonia diversifolia+ Phosphate rock, crop residues+ animal manure+ legume intercrop, crop residues+ Tithonia diversifolia+ animal manure the. The test crop will be maize (Zea mays), H516 hybrid variety. Labour data will be collected from land preparation to harvesting and threshing. The quantity of all the inputs used, including mineral fertilizers, animal manure and tithonia diversifolia will be determined. Water use efficiency will be computed as a ratio of yield, and total evapotranspiration and nutrient use efficiency will be computed as a ratio of yield to the amount of fertilizer applied. Economic and environmental sustainability will be assessed using the Data Envelopment analysis approach to determine the efficiency score. Finally, all the output will be subjected to analysis of variance (ANOVA) to assess the treatment effects, and means will be separated using Duncan multiple range at P=0.005. The efficiency scores will help in the selection of sustainable management practices.

CHAPTER ONE

1.0 INTRODUCTION

1.1 Background

Climate variability is a constraint to the agricultural sector globally (del Pozo et al., 2019). This is also the case in sub-Saharan Africa, where most of the smallholder farmers continue facing a decline in agricultural produce (Bekunda et al., 2010). Rainfall unpredictability, coupled with declining soil fertility, contributes to the declining yields (Miao et al., 2010). In Kenya, most of the smallholder farmers rely on rainfall for farming, which is not always reliable (Ngetich et al., 2014). Also, smallholder farmers in the Central Highlands of Kenya practice continuous land tillage with minimal soil replenishment, further worsening the situation. (Mugwe et al., 2009) To resolve the issue, various strategies have been implemented to increase soil fertility as well as soil water conservation, and the results have been significant (Mugwe et al., 2009; Mucheru-Muna et al., 2014; Kiboi et al., 2019). However, there is a need to assess the sustainability of these practices on nutrient and water use efficiency.

Nutrient use efficiency is an integrated reflection of the ability of soils to match nutrient supply within the root zone to the plants demand and also the plants’ ability to exploit soil nutrients, including root-zone modifications (Hirel et al., 2011). On the other hand, water use efficiency is the ratio of water used in plants metabolism to water lost by plants through transpiration (Abdalhi & Jia, 2018). These two components are determinants of crop growth and productivity. Emphasis should be focused on judicious water and nutrient management aimed at maximizing water and nutrient utilization of the agricultural sector and minimizing nutrient losses to the environment (Ghimire et al., 2017). This can be achieved through proper soil fertility management practices as widely practiced in the central highlands of Kenya (Mucheru-muna et al., 2013). This practices include the use of organic and inorganic fertilizers, mulching, legume intercrop Tithonia diversifolia and tillage practices.

Fertilisers release the essential nutrients to the soil as well as augments the soil particles increasing its water holding capacity, thereby enhancing the nutrient availability and uptake by crops (Bruulsema, 2018). Mulching, on the other hand, retains soil moisture reducing evaporation rates and the surface runoff, which erodes some of the nutrients (Assefa et al., 2019). The ultimate goal being water conservation and conserving nutrient stocks for crop uptake.

Studies carried out on tithonia diversifolia (Bekunda et al., 2010; Palm et al., 2015; Kiboi et al., 2018) have shown that it steadily releases nutrients into the soil and also binds soil particles together which results to soil moisture conservation and nutrient availability for crops. Additionally, tillage practices have an impact on nutrient and water availability (Lüder et al., 2019). Conventional tillage, which is the primary tillage system practiced in the CHK as opposed to minimum tillage, has its advantages and shortcomings (Kiboi et al., 2019). Its effects can be established instantly as it increases the decomposition of organic matter, increasing nutrient availability (Aziz et al., 2013). Also, it increases the infiltration rate increasing water availability instantly. Contrary, it leads to loss of nutrients through leaching and volatilization as well as water loss through evaporation (Krauss et al., 2017). Minimum tillage, which has not been fully adopted, is advantageous as it conserves soil moisture through the reduction of water loss as the surface cover is maintained (Hofmeijer et al., 2019). It also reduces the leaching of nutrients. However, it leads to slow organic matter decomposition making its effects not being established under short term studies (Castellini et al., 2019). This encourages farmers to continue practising conventional tillage amidst its impact over time. Therefore, it’s essential to assess the effects of these practices on water and nutrient use efficiency under a sustainability perspective.

Economic sustainability relates to strategies that enhance long term economic growth without affecting the environment (Sime et al., 2015). This implies that all the activities geared towards increasing agricultural productivity should be sustainable. In the Central Highlands of Kenya, soil fertility management techniques have shown a remarkable increase in yields (Okeyo et al., 2014). Most researchers have recommended the combined use of organic and inorganic fertilizers under conventional tillage for better results (Suge et al., 2011; Maillard & Angers, 2014). However, this may only be under short term scenario as conventional tillage leads to leaching and volatilization of nutrients as well as soil erosion. As much as it may lead to improved productivity and boost the economy instantly, the long term effects could be detrimental (Kumar et al., 2014). Minimum tillage, on the other hand, takes a long time for the results to be established hence not widely adopted (Ordoñez-Morales et al., 2019). For long term economic sustainability without environmental impacts, practices that have long-term effects should be practised.

Environmental sustainability ensures long term environmental quality (Ilahi et al., 2019). It entails the efficient use of resources without depletion. As much as more emphasis is put on economic sustainability due to the increasing population demands and reduced yields, the concept of environmental sustainability cannot be overlooked (Olawuyi & Mushunje, 2019). The effort to increase yields and conserve water by use of soil fertility management practises like mulching, intercropping, tied ridging the combined use of mineral fertilizer animal manure, crop residues and tillage has the ultimate potential of increasing yields as reported by various studies (Uzoma et al., 2011;

Bekunda et al., 2010). However, the environmental sustainability of these practises have not been assessed.

Tillage, which is the mechanical manipulation of soil for crop production, is a powerful tool to alleviate some soil-related constraints to crop productions like crusting compaction and low infiltration (Šarauskis et al., 2018). Tillage has various effects on soil physical, chemical, and biological properties, which can be detrimental or constructive (Pulido et al., 2017). This is as a result of its short and long term effects on sustainability. The most critical consequences of soil tillage on sustainability are through its impacts on the environment like soil degradation and emission of GHG from the soil-related process (Busari et al., 2015). Conventional tillage involves the complete inversion of soils, increasing the infiltration and decomposition rates. It leads to an instant increase in yields (Zuber et al., 2015).

On the other hand, conservation tillage, which includes minimum tillage, leads to water conservation and an increase in the soil aggregate stability Castellini et al. (2019). However, it takes time for the effects to be established. As the world population is increasing, the demand for food is rising, and so the need to increase the per-capita trends (Conceição et al., 2016). This results in farmers engaging in continuous land tillage to meet the demand leading to excessive exploitation of soil nutrients (Waraich et al., 2011). Therefore, as the yearning for yield increases, proper tillage should be practiced in a way that soil degradation is minimized so that soil serves as a sink rather than a source of atmospheric pollutants.

The use of synthetic fertilizers has been significant in increasing yields (Puntel et al., 2016). A reliable supply of Nitrogen as an essential nutrient for crop growth has led to an increase in crop production (Xiukang Wang et al., 2019). However, unintended adverse environmental impact emanates from the escape of reactive N from the agricultural soil through leaching leading to groundwater contamination (Bhattacharya, 2019). Additionally, excessive N application leads to the emission of nitrous oxide (N2O) and volatilization to ammonia, which are greenhouse gases that lead to an increase in the concentration of the ozone gases, which are unfriendly to the environment (Xiukang Wang et al., 2019). As much as a low amount of N application results to low yields also excess application of N can be an environmental hazard. This can be resolved through nitrogen use efficiency.

Other practices such as the application of animal manure and crop residues used as mulch promote the economic as well as environmental sustainability (Devi et al., 2017). The organic mulch conserves the soil moisture and moderates the soil temperature, reducing evaporation losses (Jabran et al., 2015). This enhances plant water use efficiency leading to increased crop performance (Hu et al., 2015). Animal manure and the incorporation of crop residues enhances the physical and soil properties (Bakayoko et al., 2009). It leads to increased soil organic matter, which promotes soil aggregate stability ( Mugwe et al., 2009). The use of these practices has been suggested to increase agricultural productivity (Kiboi et al., 2019). However, the slow and steady release of nutrients from animal manure and crop residues makes it difficult to identify their potential under a short term basis and also asses their environmental efficiency.

Environmental efficiency in agricultural systems involves producing more with less. This entails the maximum utilization of the few available resources intending to get more. This can be achieved through the application of the proper quantity of fertilizer. It also encompasses less waste disposal and pollution. As much as more soil fertility management techniques are being advocated, their environmental efficiency should be assessed to ensure sustainability. Fertilizers should be applied at recommended rates to reduce leaching, which results in eutrophication and also volatilisation of nitrogen to nitrous oxides, which contributes to greenhouse gases.

Soil fertility management techniques and tillage practice have been developed and tested in the central highlands of Kenya (Kiboi et al., 2019). They have shown a remarkable increase in yields, thereby improving the economic stability on a short term basis ( Mugwe et al., 2009). However, more focus is directed towards increasing production due to the increasing demand these practices can adversely affect the environment over time. Therefore, the study seeks to assess the sustainability and efficiency of these techniques

1.2 Statement of the problem

Declining soil fertility and climate variability highly contribute to low agricultural productivity for smallholder farmers in the central highlands of Kenya. Farmers practice continuous land cultivation with minimal replenishment leading to the depletion of soil nutrients. Besides, the low and erratic rainfall that is unevenly distributed contributes to uncertainties for the majority of the farmers who solely rely on rainfall for agricultural productivity. On the other hand, the type of tillage has a major impact when it comes to sustainability. It affects the soil water holding capacity, infiltration, evapotranspiration, among other soil properties. For increased yields, conventional tillage has been widely adopted; this is credited to the short term benefits compared to minimum tillage because it takes time for the effects to be established. Various strategies have been suggested and adopted to improve the soil nutrient status as well as soil water conservation. The results of these strategies have been significant, and various studies have reported a high increase in yields. Although these strategies can improve economic sustainability, they can also be disastrous to the environment. More emphasis is put on improved agricultural productivity to meet the increasing population demand. This overlooks the ultimate potential of these practices to impact profoundly on the environment over the long term. Furthermore, most studies are centred towards assessing the economic sustainability of these strategies due to low agricultural productivity, but there is scanty information on environmental sustainability and efficiency. Therefore, this study seeks to assess the economic and ecological sustainability of soil fertility management techniques and tillage practices in the central highlands of Kenya.

1.3 Justification

Declining soil fertility and climate variability is a risk to smallholder farmers. It has contributed to the decline in the overall agricultural production. This forces the farmers to make irrational decisions on practices that can increase yields. This involves practices like continuous land cultivation and conventional tillage. As much as these practices might be effective over a short-term basis, they can result in the depletion of nutrients and water availability for crop growth. Additionally, the continuous use of fertilizers contributes to the concentration of Greenhouse gases in the atmosphere. Also, the increased yields over the short term basis may not be consistent through the seasons. The fluctuation in the returns, as well as the environmental impacts associated with these practises, makes it essential to assess the economic and environmental sustainability of the practises. Its also important to determine the nutrient and water use efficiency to minimizes on losses and capitalize on the uptake to increase productivity. Therefore this study will asses the economic and environmental sustainability of the practices to help set the efficiency score that will help in the adoption of sustainable practises.

1.4 Research questions

1. How does soil fertility management strategies affect water and nutrient use efficiency in the Central Highlands of Kenya?
2. How soil fertility management strategies and tillage methods impact on economic sustainability?
3. How does soil fertility management strategies affect environmental sustainability?

1.5 General objective

The general objective of this study will be to evaluate the economic and environmental sustainability of selected soil fertility management strategies in the Central Highlands ofKenya.

1.5.1 Specific objective

1. To evaluate the water and nutrient use efficiency of selected soil fertility management strategies in the central highlands of Kenya
2. To assess the economic sustainability of selected soil fertility management strategies and tillage methods in the central highlands of Kenya.
3. To assess the environmental sustainability of selected soil fertility management strategies in the central highlands of Kenya.

1.6 Conceptual framework

1.7 Scope of the study

The study will cover the previous on-station experiments from 2016-2020 in the Central Highlands of Kenya. The study will first assess the water and nutrient use efficiency under selected soil fertility management practises over long term study that will result in an informed decision on the selection of the best management practices that enhance water and nutrient use efficiency. Secondly, the study will asses the economic sustainability through the yield stability approach. This will ensure consistency in yields across the season. Lastly, environmental sustainability will be assessed using the DEA approach to establish the efficiency scores that will help in the selection of sustainable management practices. The main focus of the study is on assessing the sustainability of all the implemented practices on soil fertility and water conservation practises.

CHAPTER TWO

LITERATURE REVIEW

2.0 Overview

This chapter elucidates the state of knowledge of the study topic. It covers water and nitrogen use efficiency, soil fertility management practices, economic sustainability, environmental sustainability, and data envelopment analysis.

2.1 Water and nutrient use efficiency.

2.1.0 Water use efficiency

Water use efficiency relates the above-ground biomass to the total water used (Miriti et al., 2012).[FN1]

Where Y is the total above-ground biomass while ET is the total evapotranspiration during the season, it shows the relationship between plant production and water use. This concept is of interest with the varying climate as water is a challenge to smallholder farmers who rely on rainfall for farming (Sharma et al., 2010). With the increasing rates of evapotranspiration and reduced rainfall amounts, it is necessary to quantify the water use of crops to maximize yields (Agele et al., 2011). Evaporation from the soil surface and transpiration reduce the water use efficiency of crops (Molden et al., 2010). This has led to various researchers coming up with strategies and means to quantify water use efficiency for crops.

Water use efficiency is affected by firstly the weather factors, which are rainfall and temperature. WUE relates to annual precipitation and temperature (Zhang et al., 2014). A study carried out in china Fang et al. (2010) found out that water use efficiency for maize increased over the past years, and this was attributed to increase in temperature and a decrease in precipitation. Similarly, in another study, Peñuelas et al. (2011) reported an increase in water use efficiency during high temperatures, and the justification was that crops use less water during drought conditions. However, the findings of Luo et al. (2015) concluded that water use efficiency increased with the increased rainfall amounts.

The second factor affecting WUE is tillage. Tillage is an important factor as it affects the soil’s physiochemical properties (Ji et al., 2013). The commonly practised type of tillage is the minimum and conventional tillage. Conventional tillage involves the complete inversion of soil; this exposes soil leading to high evaporation rates (Mathew et al., 2012). Additionally, it leads reduction of the soil surface cover further increasing evaporation leading to decreased WUE. A study carried out by Hu et al. (2015)concluded that conventional tillage decreased the soil water content attesting to the low water use efficiency due to high evaporation losses.

Similarly, Šarauskis et al., (2018) recorded a decrease in water use efficiency under conventional tillage due to the low water storage and high infiltration. Minimum tillage on the hand is a component of conservation agriculture, which involves minimum soil disturbance and maintains soil surface cover (Belay et al., 2019). This reduces the evaporation losses, thereby conserving the soil moisture and eventually increasing the water use efficiency (Harchaoui & Chatzimpiros, 2018). A comparison done on tillage effects on water use efficiency reported that minimum tillage led to increased water use efficiency (Zhang et al., 2013).

The last factor affecting the water use efficiency is management. This includes fertilization, planting patterns, and weeding. The application of fertiliser not only provides the essential nutrients for plant growth but also enhances root development for water uptake as reported (Li et al., 2010), especially under water stress conditions. Planting patterns affect the water use efficiency for crops (S. Zhang et al., 2014). Therefore, this calls for proper scheduling for planting for maximum water use for increased productivity. Lastly, weeding is vital in improving the consumptive use of water. Increased weeds lead to high transpiration rates and the competition of water by the crop and the weeds Russo et al., (2015) this leads to the decrease in water use efficiency for crops. WUE is an integral index in climate change research, and its a practical component for assessing the responses of the vegetated ecosystem to climate variability for sustainability.

2.1.1Nutrient use efficiency

Nutrient use efficiency (NUE) can be defined by the ability of the crop to get nutrients and utilize them in growth and production (Rakshit et al., 2015). Consequently, it can be described as the ability of the plant to absorb utilize, and remobilize the nutrients (F. Zhang et al., 2011). It is partitioned into uptake by the roots, transport through roots and shoots, and utilization efficiency (nutrient conversion to dry matter). It is assumed that under heterogeneous environmental conditions, the genetic and physiological traits of a crop primarily control NUE (Bhattacharya, 2019).

Moreover, soil properties affect NUE either directly or indirectly. The properties encompass the chemical, physical, and biophysical properties. Chemical fertilizers are among the most applied soil inputs compared to the organic inputs. The application of fertilizers such as the NPK (Nitrogen, Phosphorous, and potassium) amend the soil properties increasing the soil fertility status and boost productivity (Tong et al., 2014).

However, it has been noted that the uptake of this fertilisers is generally low. For instance, it has been estimated the uptake and utilization of N is 50% or less for Phosphorous its less than 10% and finally between 20-40% for potassium (Miao et al., 2010). This is attributed to the losses which accrue from leaching, runoff and volatilization, thereby reducing the use efficiencies of the applied nutrients (Gaju et al., 2011). Likewise, NUE is affected by agronomic practises such as the type of tillage (Abdalla et al., 2013). The type of tillage affects the level of nutrient use efficiency. For instance, the rooting pattern and development for nutrient uptake. Additionally, tillage affects the aeration and soil compaction which greatly affects NUE (Mazzoncini et al., 2011). Minimum tillage, for instance, increases the surface soil cover which increases the soil organic matter content (Yadav et al., 2017). This, in turn, increases the increases the organic matter at the top soil layer thereby forming a barrier against nutrient leaching. This makes the nutrients available for crop uptake which increases the NUE. Contrary to conventional tillage which leads to soil disturbance increases the leaching of nutrients and volatilisation of others thereby decreasing the availability of these nutrients hence low NUE (Mazzoncini et al., 2011).

2.2 Soil fertility management techniques

2.2.1 Mulching

Mulching which is an ancient practice which traces back to the last century involves the application of materials on the soil surface (Mulumba & Lal, 2008). These materials can either be straw, maize stover or plastic film. Mulching comes with a lot of advantages such as soil moisture conservation, soil quality improvement soil erosion control and increased rate of infiltration (Govindappa, 2015). It is a common practice in rain-fed agricultural systems which faces challenges of water deficit. Studies carried out in the central highlands of Kenya showed an increase in yields under the application of mulch (Xiaolin et al., 2017; Kiboi et al., 2017). This can be attributed to the conservation of soil moisture as well as soil quality enhancement. Additionally, the mulch releases nutrients to the soil for crop uptake upon decomposition increasing the nutrient availability (Bekunda et al., 2010). Although this may take a while because the decomposition process is not instant, the effects may take time to be established.

With the varying climatic conditions and long periods of dry spells, mulching is an alternative for conserving the available moisture. The increased temperature which leads to high evaporation can be minimised by mulching (Gorthi et al., 2019). This increases the soil water content for crop uptake and water use efficiency. A study carried by (Morell et al., 2011) reported an increase in water use efficiency for maize by 17 % liable to the management practises soil types and climatic conditions (Hu et al., 2015). Similarly, other studies have shown an increase in water use efficiency under crop residue mulching (Suelo et al2014). Mulching also inhibits the loss of nutrients through erosion especially under conventional tillage. Also, the volatilisation of some nutrients is minimised and this not only enhances nutrient use efficiency for crops but also controls the emission of greenhouse gases (Ghimire et al., 2017).

Mulching also suppresses weeds growth. This is a biological mechanism of controlling weeds (R. Sharma & Bhardwaj, 2018). This reduces the competition of water between the crop and the weeds. Moreover, it controls the exploitation of nutrients by the weeds. This, therefore, ensures maximum utilisation of nutrients by the crops increasing the net yield. However, this practice faces a challenge because mulching materials are always not available. Furthermore, maize stover which is always used as mulch by most farmers in the central highlands of Kenya faces competition from other uses such as construction and animal feeds (J. Mugwe et al., 2009). Sensitisation should be done to advocate for the importance of mulch especially for sustainability. This is because the application of mulch may come with short term goals like soil water conservation; however, the addition of nutrients may take a reasonable time to assess changes.

2.2.2 Organic and inorganic fertilisers

Organic fertilisers include animal manure and of crop residues (green manure) while inorganic fertilisers include the synthetic commercial fertiliser (Ghimire et al., 2017). Application of fertilisers is a requisite practise in agriculture for plant nourishment. Most smallholder farmers rely on organic since the inorganic fertilisers are expensive hence not readily available (Conceição et al., 2016). Animal manure has been used since the advent of civilisation and has been the primary soil amendments until the dawn of synthetic fertilisers in the 1940s. They are considered important because of their various advantages (Maillard & Angers, 2014).

First, animal manure augments the soil particles enhancing the physical soil properties like aggregate stability and structure (Talabi et al., 2017). This property boosts the water holding properties and also the ability of soil to resist erosion (Bandyopadhyay et al., 2010) observed an increase in the water holding capacity of soils after the application of fertilisers under long term experiments. (Bakayoko et al., 2009) also reported reduced soil erosion after the application of manure because animal manure augments the soil particles increasing aggregate stability. Secondly, manure provides the essential nutrients required for plant growth (Kiboi et al., 2019). The most common nutrient supplied by animal manure is Nitrogen (N) which is very essential for crop growth. This is very useful as it leads to increased yield (Naramabuye et al., 2008). This was similar to a study conducted by (State & Management, 2010) still proving that animal manure has the potential of improving the soil nutrient status and the overall productivity. However, the N supplied by manure takes time to form N that is available for crop uptake. This may take several months to years and this makes it difficult to establish the effects under short term study. Lastly, animal manure leads to increased soil carbon stocks thereby reducing atmospheric carbon concentration. This reduces the concentration of greenhouse gases (Maillard & Angers, 2014).

Synthetic fertilizers, on the other hand, releases nutrients faster into the soil. This is advantageous for pants in extreme distress from nutrient deficiencies (Hirel et al., 2011). Inorganic fertilisers provide the essential nutrients vital for plant growth i.e. Nitrogen, phosphorous and potassium. Various studies have shown that synthetic fertlizers improve soil quality and microbial activity (Journal et al., 2013; Kiboi et al., 2018). However, (Miao et al., 2010) reported that nitrogen and phosphorous had no effect on soil properties and this was argued that long-term application of N leads to an increase in soil nitrification. Likewise, the application of N and P does not directly increase the microbial community but lead to an increase in biomass production which aids the accumulation of organic matter (Liu et al., 2013). Other studies have observed the detrimental effects related to the use of fertilisers solely (Ding et al., 2017; Bhattacharya, 2019). This is through leaching of N into the ground water causing eutrophication and the volatilisation of N to Nitrous oxide which is a greenhouse gas. Its vital to assess the soil nutrient status to identify the limiting nutrients to restore soil quality to avoid acidifying of soil (W. Zhong et al., 2010). For better crop yields and improved soil quality, the synergetic application of mineral and organic fertilisers should be practised. This is evident from the findings of (Bekunda et al., 2010) who reported an increase in yields and water use efficiency with the combination of mineral and organic fertilisers. Similarly, (Xiukang Wang et al., 2019) reported the same findings as oppossed to the single use of mineral or organic fertilisers.

2.3 Environmental sustainability

Environmental sustainability covers a range of issues from global to specific. The global issues related to sustainability are climate change, GHGs mitigations and renewable energy while the location -precise issues are soil erosion, water management, soil quality water and air pollution (Howes et al., 2017). As much as soil fertility management practises have shown an increase in yields as well as the soil quality, their long term effects could be detrimental to the environment. For instance, the use of nitrogenous fertilisers boosts agricultural productivity; however it also contributes to the green-house gasses upon volatilisation (Devi et al., 2017). This is always often under conventional tillage method whereby the nitrogen fertilisers applied is volatilised to nitrous oxide. Similarly, the leaching of the fertilisers into water sources result in eutrophication posing a threat to water ecosystems. This collaborates with the finding of (Moldan e al., 2012) who reported pollution of water sources mainly arising from agriculcural systems. Moreover, the continued use of the nitrogenous fertilisers without substitution of organic fertilisers leads to the acidification of soils affecting the soil quality (Russo et al., 2015). A study carried out under the long term application of nitrogenous fertilisers reported a very low soil ph (Masunga et al., 2016). Also (Möller & Müller, 2012) reported a decline in the microbial communities after a long term application of nitrogenous fertilisers. This is attributed to the fact that most organisms in the soil cannot tolerate lower ph values. Continued or excessive use of these fertilisers leads to the build up of heavy metals in the soil as well as plant system not forgetting air and water pollution (Gomiero et al., 2011). The heavy metals (cadmium and chromium) contributes to biomagnification and bioaccumulation affecting all the ecosystems in the foodchain (Conceição et al., 2016). In as much as the agricultural demand is increasing with the increase in population, the use of chemical fertilisers should be done in a sustainable way to avert the adverse environmental effects.

2.4 Economic sustainability

Economic sustainability refers to the efficient and receptive utilization of the scarce resources like labour, capital, natural resources and energy (Balaman, 2019). It is an essential component as it provides long-term benefits. It also ensures the progression of healthier farming systems as well as minimizing the economic uncertainties associated with limited resources (Lee & Farzipoor Saen, 2012). There are various metric used to evaluate economic sustainability like the cost-effectiveness, profitability, competitiveness and responsiveness (Y. Zhong & Wu, 2015). However, for this study yield stability approach will be applied to assess the economic sustainability of soil fertility management techniques.

2.4.1 Yield stability

Yield stability can either be defined as static or dynamic (Tollenaar & Lee, 2002). Under static the overall performance of a crop remains constant despite the variations associated with the environmental conditions . For dynamic the crop performance varies in predictable manner in a range of environmental condition (De Vita et al., 2010). Yield stability is influenced by mainly the environment and management conditions. Most smallholder farmers engage in soil fertility management practises that enhance yields like mulching, legume intercrop and soil water conservation practises. However, these strategies do not assure yield stability. Moreover yield stability cannot be determined over short term studies (Kiboi et al., 2017).

2.4 Data envelopment analysis

Data envelopment analysis (DEA) is a nonparametric linear programming approach for assessing the efficiency and productivity of decision making units (DMUs) (Ouenniche & Tone, 2017). It allows multiple inputs and outputs to be assessed at the same time without any conventions on data dispersal (Khoshnevisan et al., 2013). Efficiency is determined in terms of a relative change of inputs or outputs. A vast number of methods have been applied to measure efficiency like the ratios and the multiple regressions analysis (J. S. et al., 2013). However, the methods are qualitative as opposed to DEA which is quantitative. Besides, they have their drawbacks. For instance multiple regression analysis assumes that there should be only one output or all the outputs be harnessed into a single indicator of production (Archontoulis & Miguez, 2015). Additionally, it measures efficiency relative to the average performance unlike the best performance. This gives little scarce information concerning the extend of efficiency profits possible at several decision making units within a sample (J. S. Liu et al., 2013). These shortcomings henceforth led to the development of DEA.

DEA has since been applied in various field, education, electricity production criminal justice recreation and healthcare. It has gained interest since the publication of the seminal paper by Charnes,Cooper and Rhodes in the 1978 (Charnes et al., 1997). Some years later in 2009 more than 700 papers were published. It was first described by (J. S. Liu et al., 2013) who suggested a novel method that syndicates and converts various inputs and outputs into a particular efficiency index. This method initially establishes an ”efficient frontier” formed by a set of decision making units (DMUs) that show best practices and then allocates the efficiency level to other non-frontier units in relation to their detachments to the efficient frontier. The simple idea has then created a wide range of discrepancies in quantifying efficiency. DEA has a lot of advantages over other methods of assessing efficiency. First, the fact that it is non-parametric no need is required to explicitly specify a mathematical form for the production. Another gain that DEA has over the other methods is its capacity to handle multiple input and output (Farantos, 2015).

2.5 Summary and research gap identified

Sustainability concept is the main focus in all agricultural systems. However, due to the increased demand with the increase in population there is need to increase productivity. This has put much pressure in the agricultural sector leading to the adoption of various soil and water conservation practises to increase yields. Most farmers especially the smallholder farmers settle for practises that serves the need at hand like conventional tillage methods that can be consequential in the long-term. Numerous studied have been done and implemented in the Central Highland of Kenya to increase soil fertility through soil fertility management techniques as well as soil and water conservation practises. The results have been significant, however most of the studies have been under short term studies hence some effects which take long to materialize like tillage may not have been established. Moreover, the studies are mainly focused on increased yields overlooking the sustainability concept which envelops the environmental and economic aspects.

CHAPTER THREE

MATERIALS AND METHODS

3.1 Study area

The research will be carried out at Kangutu primary school (00°98′ S, 37° 08′ E) in Meru south Tharaka Nithi County. Soil fertility management and soil water conservation practise have been implemented in the area and this highly contributed to the selection of the study site. The area is highly populated increasing the food demand hence putting more pressure on land (Mucheru-Muna et al., 2014). The predominant land use is maize farming which is mainly practised on small scale. The area receives bimodal rainfall distribution pattern with long rains experienced between march to mid-June and short rains between October and December (Ngetich et al., 2014). The average annual rainfall ranges between 1200 to 1400 mm. The mean annual temperature is 20°C. The area lies at an altitude of 1500 m above sea level (a.s.l) The area lies between upper midland zone two (UM 2) and upper midland zone three (UM3) Agro-ecological zones (Jatzold & Kutsch, 1982). The UM2 is the main coffee growing zone with short to medium cropping season. The UM3 is a marginal coffee zone with medium to short and short cropping season. The maize crop variety grown in this zone is the Katumani. It’s a predominantly maize growing zone. The soil is humic nitisols.

3.2 Experimental design

The field experiment was laid out in a randomised complete block design (RCBD) with treatments being a combination of tillage methods and the soil inputs. The tillage types implemented were the minimum and conventional tillage. The soil inputs were sole mineral fertiliser, crop residues, Tithonia diversifolia, rock phosphate and legume intercrop. This resulted in fourteen treatments, which were replicated four times. The animal manure was acquired from the local farms mixed and dried for two months before the application. Nitrogen was split applied at the rate of 30kg/ha during planting and 30kg/ha at knee height. Phosphorus was applied as Triple Super Phosphate (TSP) during planting at the rate of 90 kg/ha P. (Table 1). The experiment was carried out for four consecutive seasons long rains 2016, short rains 2016, long rains 2017 and short rains 2017. In minimum tillage land was prepared using a panga at 10cm depth hole in conventional tillage land was prepared by hand hoeing at 15cm depth.

Table 1; Treatment combination

Treatment (a combination of tillage and soil organic inputs)

Abreviations

Nutrient rates

N

P

Minimum tillage

Mt

60

90

Minimum tillage + mineral fertilizer

MtMf

60

90

Minimum tillage + crop residue + Mineral fertilizer

MtRMf

60

90

Minimum tillage + crop residues + Mineral fertilizer + Animal manure

MtRMfM

30

90

Minimum tillage + crop Tithonia diversifolia + phosphate rock (Mijingu

MtRTiP

90

Minimum tillage + crop residue + Animal manure + Legume intercrop (Dolichols lablab)

MtRML

60

90

Minimum tillage +crop residue + Tithonia diversifolia

+Animal manure

MtRTiM

60

90

Control

C

60

90

Conventional tillage + mineral fertilizer

CtMf

60

90

Conventional tillage + crop residue +Mineral fertilizer

CtRMf

60

90

Conventional tillage + crop residue + mineral fertilizer + Animal manure

CtRMfM

30

90

Conventional tillage+ crop residue+ Tithonia diversifolia+ Phosphate rock (Mijingu)

CtRTiP

90

Conventional tillage + crop residue + Animal manure + Legume intercrop (Dolichos lablab)

CtRML

90

Conventional tillage + crop residues + Tithonia diversifolia + Animal manure

CtRTiM

90

3.3 Data collection

3.3.1 Soil data

Soil samples will be collected at the beginning and at the end of season at a depth of 0-20 cm using a soil gauge auger. The samples will later be taken to the laboratory for the analysis of chemical and physical properties.

3.3.2 Input data

Data will be collected from the previous on-station experiments at Kangutu primary school. This will include data for the analysis of environmental and economic sustainability which entails the personnel require during mulching digging of the planting holes, planting weeding harvesting and threshing. Data on the cost of synthetic fertilizer as well as the application rates will be collected also the cost of the planting seeds, the pesticides and animal manure. Soil moisture data will be collected every week to assess the soil moisture content.

3.3.3 Output data

Above ground biomass

Maize will be harvested at maturity by omitting the guard rows, the first and the last maize plants in each row to reduce trans-boundary effects. The fresh weight will be determined immediately after detaching the cobs from the stover. Later the cobs will be sundried and hand shelled after which the weight will be determined. Stover weight will be determined at harvesting and further dried under shade until constant weight. The ultimate weight of the dry stover grain will be used to in derivation of the per hectare stover and grain yield.

Greenhouse Gases

Greenhouse gases (Carbon dioxide, nitrous oxide and methane) will be determined using vented,s tatic chamber technique to reduce sampling bias (Parkin and Venterea 2010). This is in line with the guidelines for GHGs measurements for smallscale farming (Rosenstock et al., 2013). Plastic chambers with a base and a lid will be used. The base dimensions will be (0.27×0.372×10) m and will be at a depth of 0.05-0.1 m into the soil while the lids dimensions will be (0.27×0.372×0.125) m. the lids will have vents to aid in the sampling of the gases. Three chambers will be installed per plot to minimize on variability and increase precision.

3.3 Data analysis

3.3.1 Objctive 1

The long-term nutrient use efficiency will be computed as (Hossain et al., 2005);

eq1

Whereby F is the amount of fertilizer applied in Kg ha-1 while Y is the total above ground biomass in Kg ha-1

Water use efficiency will be calculated as;

eq2

Where Y is the total above ground biomass while ET is the total evapotranspiration during the season. The data will be subjected to ANOVA in SAS 9.3 software to determine the effects of the treatments. Means will be separated using Duncan multiple range test at P=0.05.

3.3.1Objective 2&3

Inverse data Envelopment analysis will be used to establish the efficiency scores an further subjected to analysis of variance (ANOVA)in SAS version 9.3 and means will be separated using Duncan multiple range at P=0.05.

[FN1]Put the WUE formula immediately after this paragraph