East African Journal of Agriculture and Biotechnology

Dykes minimise flood risks among riparian communities. In Nyando basin, Kenya, dykes were constructed to minimise flood impacts on human activities in the riparian plains. The dyke characteristics could change the rate of silting. In spite of these dynamics, some farmers now use fertilisers as a new way of coping with nutrient deficiency. Several researches have been done in Kenya on the effects of floods on human activities; however, there is no clear link between dyke characteristics like period of existence, length and height and their influence on food crop production. The dykes in Nyando have reduced floods in the region; however, it is not clearly understood how the dyke characteristics influence the food crop. Therefore, the purpose of this study was to examine the influence of dyke characteristics on food crop production. Planning Theory was used. Descriptive cross-sectional research design applied. The target population stood at 34,460 households. At least 384 Household heads were recruited via


INTRODUCTION
In the Nyando basin, food crops majorly grown are rice, maise, beans, millet, and sorghum, and mixed cropping is the common cropping pattern utilised by the farmers (WHP, 2002).A study by Ochola (2010) indicates that flood events can result in long-term benefits to agricultural production by recharging water resource storages, especially in drier, inland areas, and by rejuvenating soil fertility by silt deposition.Floodwaters carry lots of nutrients that are deposited in the plains.Farmers love such soils, as they are perfect for cultivating some kinds of crops.An investigation by Rubin (2016) indicates that floods can distribute large amounts of water and suspended river sediment over vast areas.The study by Rubin (2016) reports that before the Mississippi and associated rivers were controlled in dykes in southern Louisiana, the rivers would frequently spill their banks.These processes made the lands of the Mississippi Delta rich and raised.
Over time, as indicated by Rubin (2016), the Mississippi area has slowly subsided with time, and without the continued replenishment of sediment from river floods, much of it has dropped to elevations below natural sea level.Therefore, there is a call for more studies on the relationship of dykes and the altitude of the wetland.This study will thus seek to investigate the subsidence of wetlands and their fertility protected by dykes.Duong (2014) indicates that the Vietnamese Mekong Delta (VMD) plays an important role in food security and socio-economic development of the country with its protection dykes.Being a lowlying coastal region, the VMD is particularly susceptible to both riverine and tidal floods, which provide, on one hand, the basis for the rich agricultural production.Triple rice cropping became possible in farmlands covered by "full-dykes'', i.e., those high and strong enough to prevent flooding.In these protected floodplains, rice can be grown even during the peak flood period (September to November).This study only looked at "full-dykes' ', that is, high and strong dykes; therefore, there is a need to provide an indepth understanding of the influence of all forms of dykes, including low and weak ones, on food crop production.Yamanouchi et al. (2022) & Adam (2008) revealed that arable farming had intensified since the middle of the 18th century, and by 1850, 60-80% of the coastal marshes were used for cereal production and the acreage of winter cereals had increased as well.Natural grasslands were replaced.The resulting homogenisation of the agricultural landscape had far-reaching consequences, as it greatly reduced the relative abundance of many species, and so, large-scale arable farming gave way to new pests and diseases: cereals were vulnerable to plagues caused by rodents and anthropophilic birds.Apparently, farmers preferred rain-spoiled years, indicating that the land had been drying up.This study reveals that the drying up of wetlands with the presence of the dykes leads to resistant pests and diseases in the farmlands.However, it does not clearly provide information on the pests and diseases.Therefore, it is necessary to provide adequate information on the pests and diseases brought by dykes that influence food crop farming.
According to Osouli et al. (2014) and Karim pour et al. (2015), raised and stronger dykes mean a reduction in incidences of overtopping and overtopping is a source of fertile silt deposition into the floodplain farmlands.On the contrary, Islam et al. (2015) report that the dykes would reduce the natural fertility of the floodplains.Consequently, farmers would potentially have to use more fertiliser applications to sustain their yields, thus creating cumulative negative impacts.A study by Buu (2013) reports that dykes that encircle large rice fields in the VMD could have negative environmental impacts in the long run, and any economic benefits farmers get will be short-lived.He states that while the dykes allow for the growing of more crops a year by keeping seasonal flooding at bay, severe degradation of soil is caused, and that would hit farmers hard.However, as he further indicates, farmers in the area are happy with the dykes, for they have boosted incomes sharply.Farmers have been able to cultivate the third crop every year and earn higher incomes.Experts, however, as indicated by Ni (2004), say the dykes cause greater harm than farmers realise.Ni (2004) notes that in Vietnam, dykes have blocked the inflow and outflow of flood waters into the Plain and the Quadrangle, and that would create serious problems.Floods bring alluvia to the soil, giving nutrition back to the land after crops and the alluvial deposits during the flooding also help strengthen the weak stratum of the "young delta," which also, after several months, when the flood gets out of the fields, carries the waste of chemical fertilisers and pesticides out to the sea.This study provides sufficient information that reveals flushing out operation freshens the fields for the new crop, which means fewer pests and diseases.Therefore, there is a need for more information on the influence of dykes on food crop production with reference to undrained chemicals and fertilisers.
A study by Tuan (2004) indicates that the dykes have changed the nature of the delta.Studies done by Ni and Tuan (2004) have also shown that soil quality in rice fields has degraded strongly after five or six years of cultivating three crops each year.They express concern about the losses farmers face now and in the future.This is a shortsighted approach as profit and other benefits from the encircling dykes cannot make up for the impacts on the environment, as well as long-term socio-economic impacts.A study by Ni (2004) reports that Farmers in the delta acknowledged that they do recognise the degradation of soil.However, the studies provide inadequate information on the level of degradation.Therefore, there is a need to clearly reveal whether the presence of dykes degrades soils such that they negatively influence food crop production.Mutai (2009) observed that dykes have led to reduced soil moisture and the changing in cropping calendars and have an effect of reducing production in crop fields.However, this study did not look at other dyke-characteristics: height and strength.This study seeks to evaluate these dyke characteristics and their influence on food crop production.A study by Mahn et al. (2014) indicates that the dyke networks are designed to protect crops from intense flooding events and to provide year-round irrigation, and the compartments which are formed facilitate highly productive agriculture in deltas around the world, such as the Mekong as studied by Hung et al. (2014).With declining fluvial sediment loads, such networks disconnect floodplains from their rivers and potentially limit the supply of fluvial sediment reaching the surface of the delta.Therefore, this study seeks to clearly highlight the influence of the dyke networks on food crop farming and fluvial load deposits on the floodplains.
A study by Venterink et al. (2006) reports that sediment deposition in compartments is important for maintaining dyke surfaces above rising sea levels, and nutrients that are bound to deposited sediments make deltaic soils and ecosystems some of the most productive.A study by Nixon (2003) indicates that the continued provision of such natural nutrients can, therefore, reduce the need for costly chemical fertilisers.A study by Ibáñez et al. (2013) states that farmers have been making the economic benefits of natural sediment deposition for centuries through practices such as digging sediment out of the canals and spreading it over the floodplain in the Nile Delta, engineering siltation projects, and in the Ebro Delta and making strategic decisions on dyke height which allow overflow, as indicated by Manh et al. (2014) it was traditionally the case in the Mekong Delta.Ibáñez et al. (2013).This has grown in significance in recent years as strategic sediment delivery for land-building has been identified as a key adaptation strategy to sea-level rise (Ibáñez et al., 2013).Therefore, there is a need to provide information on dykes and maximum sediment deposition in relation to food crop farming.
In Bangladesh, India, vegetable cultivation and other crops on pond dykes are encouraged.A study by USAID (2016) shows that dyke farming increases women's economic empowerment.Vegetable production would ultimately ensure food security and that the study area respondents produced on average 218.47 kg of vegetables annually from one decimal dyke area, which is completely overproduction.The fallow dyke areas are brought under vegetable cultivation by using improved methods.A study by Jafrin et al. (2009) states that dyke cultivation practices to grow vegetables in small patches of land require no chemical fertilisers or pesticides.Bloemertz (2014) noted that the impact of flooding on crop farming has continued to be of great concern since agriculture is the backbone of the economy; it creates employment and earns foreign exchange.Opere (2013) says that this has raised debate on the farming practices not only in Kano floodplains but also in Budalangi.It is evident from these areas that crop farming had been compromised by floods, and the Government of Kenya, in association with other non-governmental organisations, took measures in the construction of dykes to manage floods in these areas.For instance, as studied by NRC (2006), in Budalangi, the National Water Conservation and Pipeline Corporation engineers who had worked at the Budalangi Dyke rehabilitation Project appealed to the Department of Agriculture to advise the farmers on the consequences that would be caused by the destruction of the dykes.According to Okayo et al. (2015), the dykes have managed various areas affected by the floods and the flood zones have attracted agricultural activities; crop farming due to the naturally enriched alluvial soils from the silt load.According to NRC (2006), residents of Budalang'i in Busia District are satisfied with the flood control measures implemented by the Government, and Budalang'i is now lush greenbecause the maise, beans, cassava, groundnuts, and vegetables are flourishing despite the heavy rains that continue to pound the area Huho & Kosonei, (2014).According to the study by Okayo et al. (2015), residents like the new trend after many years of crop losses and disease.This study focuses on the increase of farms and farmlands but does not clearly indicate the dyke characteristics that would have caused these changes.Therefore, this study seeks to assess the dyke characteristics that influence food crop farming.

Study Area
The lower River Nyando basin (Figure 1

METHODOLOGY
The descriptive cross-sectional research design was found suitable for the study because data dykes' characteristics collected at an instance could explain the variation in food crop production.The target population was 34,460 households; a sample of 384 household heads was derived using Fisher's formula.Based on the assumption of homogeneous population distribution, systematic random sampling was applicable.The main data collection tool was a questionnaire; however, key informants, focused group discussions, photography, measurements, and observation were also included in the survey.Using mixed data collection tools helps in minimising bias.About 10% of questionnaires were pretested, and a Cronbach's reliability analysis was performed; a coefficient of (r = .71)was realised.Given the strong reliability, the instrument was applied without further correction.Data was coded and organised depending on themes; the quantitative data and linear coefficient of determination were then analysed using SPSS and data presented in tables, figures, or plates.

Distribution of Food among the households Bordering Dykes
The majority (50%) of the households in the lower Nyando basin relied on farming (Table 1).This was closely supplemented with food bought from the market at (25%).Less than 10% of the households depended on donations and other sources.In the period 2018 to 2022, it is reported that the households were adopting more crop farming in the greater western Kenya and Nyanza region (Oduor, Mutavi, & Long'ora, 2022).The increased crop farming uptake implies that many of the farmers whose farms bordered dykes benefited from the ongoing dyke construction and reconstruction.These findings agree with Huho (2005) that farmers increased their activities on dry farms and with the dykes as security at Budalangi.29% reported no change.This implies that even with the dykes there was no change in food crop farming.A study conducted by Rogger et al. (2017) examined climate change markers.He concluded that reduced rainfall amounts with climate change led to food crop failure.The study area has those who do not know if food crop yields have increased and no change, respectively.This can be explained by overtopping and water not flowing back to the channel.Through observation, overtopping river flows can reach into the farms, causing severe floods and decreased food crop yields.GOK (2008) reports that farmlands are destroyed in overtopping in Budalangi, raising the fear of food shortage.Olufemi et al. (2020) observe that overtopping is a major environmental disaster affecting mankind, ranging from crop destruction.This finding agrees with that of Olufemi et al. (2020) in that overtopping reduces food crop yields on a large scale.The recently constructed dykes (table 3) had the lowest crop yields, while older dykes were associated with higher food crop yields.This was possibly due to the fact that most older dykes were worn out or perforated, allowing fertile silts into the crop fields (Week & Wizor, 2020).).Fertile crop fields have been known to positively influence crop health and vigour (Ajaero, 2017).).The results (Figure 2) show that most food crops were found in areas covered by short and low dykes (25.93%) respectively.However, areas with no dykes (7.41%) registered the lowest yields.This is because of the reconstruction period of the dykes-2017 (GOK, 2018) and continuous repairs.
According to GOK (2018), dykes' construction in the River Nyando was to minimise the perennial migration and food crop loss.A Focused Group Discussion was reported; Low and short dykes along the lower river Nyando are good for crop production because they easily allow nutrient-rich water into the farms and are easy to drain out.Respondents (Table 5) were asked to state, ´´If their food crop yields increased, decreased, had no change, or did not know if there was a change in the food crop yields.The results from the table indicate that; In the areas not covered by dykes, the respondents intimated that 64% had no change in crop yields, 26% had decreased yields, 8 % increased yields, and 2% did not know if there was a change.This implies that a majority did not experience in their food crop yields.According to Musah, Mumuni, Abayomi & Jibrel (2013), the period of exposure to a given function influences the level of adaptation to that function.This agrees with the findings that areas with no dykes expose farmlands to no dynamics of the function dykes hence no change.This is followed by the influence of decreased yields.This implies that areas with no dykes have experienced a decrease in food crop yields.Through observation, the study was able to obtain that flood waters still get to the farmlands destroying crops and the dykes upstream acting as barriers to the water flowing back to the channel.This finding is consistent with the study of Ajiboye & Orebiyi (2022), that dykes along the Mississippi River stop water backflow.A small group of 8% reported increased yield.This implies that even with their farms exposed to the river waters, their yields have increased.
According to Kaida (1991), Sedimentation on Aswan High Dam decreased silt deposition on farmlands.The absence of dykes encourages rich silt deposition encouraging food crop growth and yields.In areas covered by perforated dykes, 52% of the respondents had decreased crop yields, 28% increased yields, 17% had no change, and 3% not knowing if there was a change in their crop yields.
Along the washed-out dykes, the crop yields were at 54% for decreased, 38% for increased yields, 8% for no change, and 2 % did not know if there was a change in the yields.Along the compromised dykes, 49% had increased yields, 44% decreased yields, 6% no change, and 1% recorded not knowing if the food crop yields increased.

Dyke Height and the General Crop Yield
The information on the relationship between dyke height and crop yield was sourced and presented as shown in Table 6.The study sought to find out the influence of dyke height and food crop production.Responses on dyke height indicated (Table 6) that where there were high dykes: increased yields were at 52%, decreased at 40% and no change at 8%.Equally, on low dykes: increased yields at 58%, decreased at 40%, and 2% reported no change.This means that areas with high dykes had a lower percentage increase as compared to low dykes.This can be explained by the fact that low dykes experience overtopping, which introduces silt deposition to the farms increasing yields.This agrees with the study by Pandey (2015), sedimentation on Aswan High Dam decreased silt deposition on farmlands.The absence of dykes encourages rich silt deposition encouraging food crop growth and yields WRMA (2014).

Dyke Age and the General Crop Yields
The information on the relationship between dyke age and food crop distribution was sourced and presented as illustrated in Table 7.The study (Table 7) also investigated the influence of age of dykes and food crop farming.Food crop farming and age of dyke responses were as follows: before 2016 increase in yields at 54%, decreased yields at 30%, no change at 10% and 6% did not know whether the yields increased.2017 and beyond, increased yields at 62%, decreased yields at 26%, 10% reported no change and 2% did not know if there was a change in food crop yields.This means that farmers who have had dykes for longer enjoy more yields than those who have had them for a shorter period.The areas that have had dykes for a shorter period have experienced a reduced percentage increase as compared to those with dykes for a longer time.Supported by Banerjee (2010), the period of exposure to a given function influences the level of adaptation to that function.This agrees with the findings that areas with longer existing dykes expose farmlands to dynamics like flood barriers hence increasing yields Van der Ven, (2004).This is followed by a decrease in crop yields due to silt nutrient depletion Redd (2017).In food crop farming, 68% of the households reported poor yields in the last year (Table 8).24% had fair yields, while 3%, 4% and 1% experienced good, very good and excellent harvest, respectively.A total of 90% of the respondents ranked their harvest fair and below.
Table 4 shows food crop yields by households in the last year.
Most maise farmers reported poor harvests (See Plate 1), while a number of farmers of crops such as sorghum and cassava reported very good and even excellent yields.This means that farms with maise recorded reduced yields, but those with sorghum and cassava recorded higher yields (Table 4).This can be explained by cassava and sorghum doing relatively well in infertile farmlands.An indication that there is an influence of dykes on food crops.The majority of respondents agree that there is an influence of dyke on food crop production.Similarly, according to Buu (2013), Sedimentation on Aswan High Dam decreased silt deposition on farmlands.Dykes discourage rich silt deposition reducing soil fertility and reducing food crop yields.This showed that there is an influence of dykes on food crops.Again, Okayo et al. (2015) report that in Budalangi, agriculture improved after the construction of dykes along River Nzoia.This study agrees that there is an increase in food crop production.The research (table 9) found that 45.4% (R 2 = .454,p = .039) of the variation in the general crop yield was explainable by the combined change in Dyke Characteristics.The reanalysis of the linear model (table 10) indicated that the Age of the Dyke (t = -1.759,p = .033)was linear, with a statistical significance of prediction; however, it was negatively related to the general crop yield.
Conversely, the Height of the Dyke (t = 1.522, p =.21) and the length of the Dyke (t = 2.911, p = .049)had a significant positive linear association with the general crop yield in lower Nyando.The results identified by Gadain et al. (2006) noted that the period of exposure to a given function influences the level of adaptation to that function.Longer and higher dykes should be constructed to protect larger crop farming areas and to protect crops from floods related disasters.However, Dykes should be constructed with controllable floodgates to allow silt and nutrients into the adjacent farms (Bunn and Arthington, 2002).It is recommended that further research be conducted in the same region to determine the coping mechanisms of the residents with the influence of dykes on their livelihood activities (Takago A. et al., (2016).It would be of interest to study and policymakers in developing appropriate flood mitigation measures and also creating awareness.This means that food crop production significantly depended directly and indirectly on the dykes' characteristics (Friend, 1990).
According to GOK (2018) reports, the dykes were reconstructed in 2017 in the Lower River Nyando when it was realised that apart from household displacements, crop fields were becoming more vulnerable to unprotected river banks.A key The dykes along the lower river Nyando basin were first constructed in the 70s.Reconstructions to a small scale have since been done by locals and major ones done by the national Government, like in 2003Government, like in , 2007Government, like in and 2012.The county government of Kisumu constructed dykes along the river in the last quarter of the year 2016 as a response to the major floods in the region at the time.Very few NGOs (JICA affiliate) have partnered with WRMA, too, in the reconstruction of these dams.

CONCLUSIONS
The variation in dykes' characteristics significantly influenced crop production in the Nyando basin.Both the length and height of the dyke had a positive influence on crop yield.However, the age of the dyke showed a significant negative influence on the overall crop yields.The current study findings show that most households in the lower River Nyando basin have had the dykes influence crop production.There are significant differences in food crop farming.This means that there has been a significant increase in food crop farming with farmers exploiting the fertile silt deposits (locally known as "Mo") trapped back by the Dykes.
) is within Kisumu County.The River traverses both the Nandi and Kericho counties before causing annual flooding havoc in the lower Nyando basin.It has been associated with massive crop failures in the recent past due to sheet erosion.It has a catchment area of 3450 square kilometres and is about 153 kilometres long.It occupies two-thirds of the lower half of the Nyando River catchment.The Lower section of the River Nyando has several tributaries and distributaries, viz.R. Nyamasaria, R. Miriu, R. Orongo, Awach Kano, Nyaidho among others.The River Nyando originates in the Tinderet forest, where it collects nutrients from well-fertilised farms from the Rift Valley (Integrated Flood Management for Nyando River basin-Main Report, 2014).Farmers within the basin have been tempted to interfere with dykes, perhaps to allow the flow of the rich silt into the crop lands leading to annual flood menace.Dykes have been constructed and reconstructed to address the flooding challenge since 1975.

Figure 1 :
Figure 1: A Map showing the location and outline of the study area

Figure 2 :
Figure 2: Distribution of Crop farms by dykes' characteristics

Table 4 : Dykes height and Food crop Distribution
The results (table 4) indicated that the distribution of the high and low dykes was nearly equal.According to the Ochieng, Charles, & Ang'awa (2017) report, the county government of Kisumu constructed dykes of 0.7 m along the lower river Nyando to curb floods.On the basis of observation, the height of dykes in the study area is nearly equal because of construction by one body, that is, the County Government of Kisumu, apart from areas where construction was carried out by private developers: with low dykes (0.7 m) at 53.85% and high dykes (1.3 m and above) at 46.15%.

Plate 1: Crop Failure in farms with reduced soil fertility and drought Dykes' Characteristics and the General Crop Yields Table 9: Influence of Dykes' characteristics on the general crop Yields
a. Predictors: (Constant), Dykes length (Metres), Dykes age (Years), Dykes' height (M