East African Agricultural and Forestry Journal

Factors Affecting Adoption of Integrated Soil Fertility Management Technologies in Machakos and Bungoma Counties, Kenya

Emongor R. A. — 2023-01-09

Common bean is an important pulse crop in East Africa. Bean yields have been low and on the decline in Kenya. The decline in bean yields has been due to biotic and abiotic stresses, such as low rainfall, pests and diseases, low soil fertility, among others. Research was carried out to determine factors that influenced adoption of Integrated Soil Fertility Management (ISFM) technologies in Bungoma and Machakos counties, Kenya. Multi-stage sampling procedure was used to randomly sample 502 smallholder farmers in Bungoma and Machakos counties. Primary data was collected from sampled farmers by carrying out face-to-face interviews using a structured questionnaire. Collected data was analysed using descriptive statistics and Logistic regression. Descriptive statistics results showed that the adoption and use of ISFM varied in the two counties. For example, approximately 32% of farmers in Machakos County did not use ISFM technologies compared to 14% in Bungoma. Approximately 33% of the sampled farmers in Machakos County used manure compared to 8% in Bungoma County. The Logistic regression results showed that region, level of education of the household head, access to extension services, whether the household was food secure and availability of markets for beans significantly influenced the choice of ISFM by farmers. Therefore, to improve adoption of ISFM, there is need to strengthen the extension services and improve bean markets in the study sites.

Effect of Tillage, Liming and Cropping Systems On Maize Yields in Different Agroecological Zones in Kenya

Githunguri C. M. — 2023-01-10

Negative effects induced by climate change have contributed to reduced global yields of maize. There is therefore need to endow farmers with innovative and transformative climate smart agriculture technologies to urgently address food insecurity and the realities of climate change in cereal growing regions of Kenya. Technologies have been generated for improved maize and beans production and their impact has not been fully felt. In this study, technologies and innovations on tillage, liming and cropping systems that can improve maize and beans production were evaluated and demonstrated to farmers in different agro-ecological zones in Kenya with the aim of enhancing their adoption. Trials were established at KALRO-Njoro, KALRO-Kakamega, KALRO-Kitale, Baraton University, and Mabanga Agricultural Training Centre, in Nakuru, Kakamega, Trans-Nzoia, Nandi, and Bungoma Counties, respectively. The tillage treatments evaluated included conventional, tied ridges, minimum and zero tillage planted in plots applied with 2 t/ha of lime or without lime. The cropping systems evaluated were maize intercropped with beans or sole cropped maize. A split-split plot design with four replications was used. Results indicated that conventional, tied ridges, and minimum tillage produced higher (P<0.05) yields than the zero tillage with or without lime irrespective of the cropping system in Nakuru, Nandi and Trans-Nzoia Counties. In Nandi, Kakamega and Bungoma Counties, there were no differences (P>0.05) between the four tillage systems.

Overcoming Soil Acidity Constraints Through Liming and Other Soil Amendments in Kenya. A Review

Esilaba A.O. — 2023-01-10

Food production in Kenya is constrained by low and declining soil health resulting from low soil fertility and increasing widespread soil acidity, coupled with emerging climate change effects leading to recurrent food and nutrition insecurity. The major food production areas with high crop yield potential in the country are greatly affected by soil acidity due to continuous cropping, loss of organic carbon, nutrient leaching and inappropriate use of fertilizers. While use of organic and inorganic fertilizers, improved seed varieties and crop protection have received much research attention, liming as one way of improving soil health and crop production has not received similar attention. Consequently, potential yield of hybrid crops remains constrained. Soil acidity is mainly ameliorated by applying lime or other acid‐neutralizing materials, which neutralize the acidity, raises soil pH, increases the availability of plants’ nutrients and adds calcium and magnesium to the soil. It also improves the environment for beneficial soil microorganisms thus enhancing rapid breakdown of organic materials in the soil and releasing nutrients for growing plants. Soil buffer capacity determines the amount of lime per unit of soil volume needed to alter soil pH. Soils with low Cation Exchange Capacity (CEC) respond rapidly to liming than soils with high CEC. But the low-CEC soils have a high capacity for rapid leaching of the added bases, thus a quicker return to original acidity unless additional liming is done. Over-liming is recommended for soils which have low CEC, such as sand which is deficient in buffering agents such as organic matter and clay. There is therefore need for appropriate attention to to ameliorate soil acidity in order to maintain good soil health for food and nutrition security. A meta-analysis of a desk study supported by field experiment was carried out in areas viewed as most affected by soil acidity. The aim of the study was to evaluate amendments that can be used for alleviating soil acidity in acidic soils. The results showed that extensive work has been done in Western and Rift valley regions of Kenya targeting soil acidity alleviation and few studies in the coastal and eastern regions due to perception that these areas do not have acidic soils. Among the soil acidity amendments, use of lime and organic sources showed positive crop response and increased yields when applied in acidic soils.

Variations in Plant Nutrient Allocation, Physiological Development Patterns and Soil Structural Characteristics as Influenced by Zero Tillage Systems in the Central Highlands of Kenya

Kinyua M.W. — 2023-01-10

The global food requirements are projected to rise above the current demand. Surface application of residues in zero tillage results to nitrogen immobilization, posing nutrient use efficiency challenges, while tillage and crop residue removal destroys soil structure. Little is documented on how integrated use of crop residues and inorganic nitrogen under zero tillage could affect plant nutrient allocation, physiological development, and soil structural improvement relative to conventional tillage systems. A study was conducted to: (i) assess how nitrogen and phosphorus accumulation in maize grain and stover are affected by application of different rates of residue and inorganic nitrogen in conventional relative to zero tillage systems, (ii) examine how maize development is influenced by application of different levels of residue, inorganic nitrogen and tillage and (iii) assess how application of residues, inorganic nitrogen and tillage influence soil aggregate stability. An on-station trial was set in a randomized complete block design replicated three times during the 2015 short rain season. Six treatments were laid, comprising a combination of different rates of maize stover residues (0, 3 and 5 tons/ha) and nitrogen as urea (0, 80, 120 kg/ha), in conventional relative to zero tillage systems. Soil was sampled to assess nitrate- nitrogen concentration at four depths, namely, at sowing, 8th leaf, 10th leaf and dent stage, soil carbon and aggregates at the four depths at the end of the season. Minidisc infiltrometer of 0.25 radius was used monthly to assess treatment effects on soil hydraulic conductivity and leaf chlorophyll recorded every fortnight from maize topdressing to tasselling using SPAD-502 meter. Analysis of variance was done using GenStat analysis software 14th edition, means separated using least significant difference (P≤0.05). Residue application in conventional tillage increased nitrogen (56%) and phosphorus (29%) allocation in maize grain compared to when equivalent rates of inputs were applied in zero tillage while increasing residue quantity from 3 to 5 t/ha increased grain phosphorus allocation by 24% (P≤0.05). When equal rates of inputs were applied in zero and conventional tillage, the latter had taller (12.3%) plants (P≤0.05) but with similar leaf area index and chlorophyll content as those of zero tillage. At 0-5 cm, the large macro aggregates were affected by depth and treatment × depth interaction (P≤0.01) with zero tillage+5R+80N having 41% higher large macro aggregates than zero tillage+3R+80N. The ability of zero tillage+5R+80N treatment to increase grain phosphorous allocation, moderate leaf nitrogen levels through maize vegetative stages and produce higher macro aggregate proportions prompts its consideration as a best nutrient management zero tillage strategy for central highlands of Kenya. Its feasibility under mixed farming system characterized by stiff competition for stover with the livestock component requires a further study.

Yield Response of Finger Millet (Eleusine Coracana L.) to Poultry Manure Application in Western Kenya

Makete N. N. — 2023-01-10

Declining soil fertility is affecting finger millet production in western Kenya and inorganic fertilizer use is expensive for most small holder farmers. With over 90% of farmers keeping poultry, its manure appears to be a potential alternative source of fertilizer for finger millet production. An experiment was conducted at KALRO - Kakamega to evaluate the yield response of finger millet (Eleusine coracana L.) to different rates of poultry manure (0, 5, 10, 15, 20, 25 and 30 t/ ha). This was carried out during the long rains season (March - August) and short rains season (September - December) of 2016. Experimental layout was a Randomized Complete Block Design with three replications. Results indicated significant yield increase from 1,148 kg/ ha (control 0 t/ ha rate) to 1,925.9 kg/ ha (5 t/ ha rate), which was significantly different from the 10 t/ ha rate (2,463 kg/ha) during the long rains season. No significant yield increase was observed beyond 10 t/ ha. Similarly, no significant yield difference was recorded with increasing rates of poultry manure during the short rains season. This clearly indicated that, during the short rains season, finger millet yield may have been affected by other factors besides poultry manure rates. Significantly higher mean yields were recorded during the long rains (2,431.7 kg/ ha) when compared to the short rains season (936.5 kg/ ha). The positive yield response of finger millet to increased rates of poultry manure application during the long rains season indicates that smallholder farmers can consider using poultry manure (5-10 t/ha) as an alternative fertilizer for finger millet production.

Integrating Different Soil Fertility Managements Practices Towards Improving Rain-Fed Maize Productivity in The Central Highlands of Kenya

Muriithi C. — 2023-01-10

Low maize productivity in central highlands of Kenya is contributed by various factors, such as low soil fertility, poor agronomic practices, minimum use of agricultural inputs, pest and diseases and use of recycled seed. Soil fertility decline has the greatest contribution to this low productivity. The objective of the study was to evaluate nutrient management technologies on acidic soils using organic and inorganic commercial fertilizers to improve soil fertility and to monitor soil pH status following application of these enhancements. The study was conducted in six counties; namely, Nyeri, Embu, Kirinyaga Meru, Murang’a and Tharaka Nithi. The test crops were two maize hybrids; that is, H517 and Duma 43. The plots were laid in Randomized Complete Block Design and replicated three times in different counties. The plot size was 10 m × 10 m. At harvest, the outer rows on either side of the plot and the last plant in each row were removed and data collected from the middle rows. The treatments included NPK 23.23.0 at 250 kg/ ha + cattle manure at 5.0 t/ ha, Mavuno fertilizer applied at 250 kg/ ha + cattle manure at 5.0 t/ ha, and cattle manure alone at 5.0 t/ ha. The three treatments were applied in furrow and tied ridges, as well as on the flat bed, with all the plots being top dressed with CAN at 60 kg/ ha at knee height. Data were subjected to Analysis of Variance (ANOVA) and the means separated using the Least Significant Difference (LSD) method. The results showed significant differences in plant height (P < 0.0017) across the treatments. A combination of Mavuno blend fertilizer and manure applied on furrow and tied ridges produced the tallest plants (232.80 cm), highest weight of stovers (10.05 t/ ha) and highest grain weight of 6.67 t/ ha, while manure alone applied on the flat bed recorded the lowest grain weight (4.16 t/ ha), plant height (185.60) and stover weight (4.28 t/ ha). Therefore, small-scale farmers have a potential of increasing yields through integration of furrow and ridges combined with Mavuno blend fertilizer and manure.

Effect of Maize-Cowpea Cropping Patterns On Soil Moisture Conservation in Meru and Tharaka Nithi Counties

Mwenda K. I. — 2023-01-10

Given the frequent drought pressure caused by the unpredictable and limited precipitation concurrent with global climate change, highly efficient cultivation technologies have been increasingly recognized by various levels of scientific communities. Maize (Zea mays L.) based intercropping systems are widely practiced in Kenya, but only a few studies have focused on cowpea (Vigna unguiculata L.) as the companion intercrop in moisture conservatory strategy. This study was conducted during the 2018 long rains of March-April at the Kenya Agricultural and Livestock Research Organization (KALRO) Igoji Research Station and Magutuni Primary school in Meru and Tharaka-Nithi Counties, respectively. The objective of the study was to assess the effect of incorporating cowpea into the maize production pattern on crop cover and soil moisture content. The experiment was laid in a randomized complete block design with three replications in 3 x 4 m plots. The treatments comprised of pure maize stand, maize intercropped with inoculated cowpea, maize intercropped with non-inoculated cowpea and pure non-inoculated cowpea. A generalized linear model was used to determine the effects of cropping patterns on ground cover, leaf area index and soil moisture content, using GenStat 19th edition. Means were separated using Fischer’s protected least significant difference (LSD) test, with differences considered significant at P≤ 0.05. Significantly (P≤ 0.05) higher (82%) crop cover was exhibited at kernel development stage in maize intercropped with inoculated cowpea compared to 78, 64 and 53% in maize intercropped with non-inoculated cowpeas , sole stand of non-inoculated cowpeas and sole maize stand, respectively. Similarly, the highest soil moisture content was recorded at kernel development stage: 210.3, 209.3, 200.2 and 196.4 mm in maize intercropped with inoculated cowpea, maize intercropped with non-inoculated cowpeas, sole stand of non-inoculated cowpeas and sole maize stand, respectively. Relative to sole maize stand and sole stand of non-inoculated cowpeas, maize intercropped with inoculated cowpea recorded the peak leaf area index of 3.75 at 70 days after planting at Igoji and 3.16 at 63 days after planting in Magutuni. The study showed that cowpea is a promising legume crop that could be integrated into maize cropping patterns to improve moisture conservation.

Integrating Inorganic and Organic Fertilizers in Cropping Systems for the Transformation of Maize Productivity in Nakuru County

Ooro P.A. — 2023-01-11

Despite the immense significance of maize (Zea mays L.) for Kenya’s economic prosperity and food security, productivity and production have not significantly increased over time. This is attributed to a number of things, including decreased soil fertility. In order to ascertain the applicability of Integrated Soil Fertility Management (ISFM), a study was carried out between 2016 and 2017 in Nakuru County at the Kenya Agricultural and Livestock Research Organization (KALRO), Njoro Centre, Nakuru County. The treatments were arranged in a split-split plot in a randomized complete block design (RCBD) replicated four times. Soil and water conservation (SWC) and conventional tillage (CT) were allocated to the main plot, the split-plots and fertilizer sources i.e Farm yard manure (FYM), Nitrogen (N) and Phosphoros (P) fertilizers to the split-split plot. Kenya Seed Company maize hybrid (H6213) and Egerton bean variety (Chelalang) were used as test crops. A variety of maize and bean (Phaseolus vulgaris L) characteristics, such as plant stand at germination, plant vigor, days to 50% blooming, days to 50% maturity, plant stand at harvest, number of pods per plant, number of cobs, number of seeds per pod, grain yield, and 100-grain weight, were all recorded. Applying a full rate of inorganic fertilizer resulted in significantly maize yields (P< 0.05) compared to all other fertility management strategies, with the exception of those where a half rate of both inorganic and organic fertilizers was applied. The results further showed that the use of inorganic fertilizer alone considerably increased maize output whether cultivated as a sole crop or an intercrop compared to farmyard manure applied alone or in conjunction with inorganic fertilizer. The application of inorganic fertilizer either alone or in conjunction with farmyard manure significantly (P< 0.05) increased the grain production of maize, which suggested that maize would benefit from ISFM options. The results generally indicated that maize was a good competitor in an intercropping system of beans and maize, which reduced the output of beans.

Integrated Soil Fertility Management Prospects for Soil Productivity and Food Security in Machakos County

Wamalwa S. W. — 2023-01-11

Integrated soil fertility management is the most cost-effective and time-efficient method of restoring soil fertility and increasing per capita yields on Sub-Saharan African smallholder farms. However, low acceptance has resulted from a lack of knowledge about the prospects of these strategies prior to promoting them. In 2016, the Mwania watershed in Machakos, eastern Kenya, was surveyed to fill this void. About 174 household heads were chosen using the “farmer-led adoption approach and a pretested structured questionnaire to obtain primary data on their household gender, education level, food security, cultivated land size, soil fertility practices, and constraints to determine the potential use of integrated soil fertility management practises at the watershed level. Data were analysed using the Statistical Package for Social Sciences Version 22 computer program for descriptive attributes. Relationships between dependent and independent variables were determined using the tobit regression model. According to the findings, 85% of households are headed by men, with over 82% being post-primary graduates, who are the main decision makers. The majority (83%) cultivate 2 ha and 57% acknowledged food insecurity, with 89.1%, 73.1%, and 45.1% blaming it on climate variability, limited soil moisture, and a lack of input access, respectively. Low fertility scored 40% at medium level with labour at 40% in low cluster constraints, could be because of high unemployment rates. Animal manure and chemical fertiliser use were reported at 95.5% and 76.6%, respectively, although they were using them separately, probably due to high cost, increased labour requirements, and accessibility problems resulting in continuous low yields. Therefore, huge prospects of integrated soil fertility management practices’ use exist in the Kenyan semi-arid, especially when promoted at community level.

Soil Aggregation, Organic Carbon and Microbial Biomass as Affected By Tillage, Residue Management and Cropping Systems in Tropical Ferralsols of Western Kenya

Bolo P.O. — 2023-01-11

Soil aggregates are important indicators of soil health, nutrient status and ability to resist erosion. This parameter is sensitive to soil disturbances that occasion disintegration of aggregate sizes, loss of organic carbon and physical killing of the soil dwelling macro- and micro-fauna. Numerous agronomic practices are promoted to enhance sustainable food production, but little concern has been taken on the effects of such practices on soil aggregate stability and microbial biomass and soil organic carbon, yet these are vital indicators of soil health, nutrient availability and structure maintenance. A study was conducted in western Kenya to assess the effects of tillage, cropping systems and residue management on soil aggregate stability, microbial biomass carbon and soil organic carbon in 2017 and 2020. At both depths assessed (0-5 and 5-15 cm), tillage, cropping systems and residue retention significantly (P ≤ 0.05) affected soil aggregate stability indices. Mean weight diameter (MWD) was significantly higher (P ≤ 0.05) in; Reduced tillage (RT) than conventional tillage (CT) (P ≤ 0.05), maize-soybean intercrop compared to rotation system (P ≤ 0.05), and in residue retention compared to residue removal treatment (P ≤ 0.05). In 2017, microbial biomass carbon (MBC) was not significantly affected by either tillage, reside retention or cropping systems, but was 23 and 29%, respectively, higher in reduced tillage and maize-soybean intercropping systems respectively. In 2020, MBC positively correlated with total nitrogen, SOC and S as opposed to 2017. Soil organic carbon (SOC) was not significantly affected by treatments, but was slightly higher in residue retention (3.57%) and maize-soybean intercropping systems (6.0%). In 2017, large macro-aggregates (LM) at 5 cm depth significantly negatively correlated with Mn while LM (at 15 cm) positively correlated with soil pH, K and Mg. Small macro-aggregates (SM) at 15 cm positively correlated with S but negatively with Al (at both depths), P and Fe. Micro-aggregates (M) at 15 cm positively correlated with P and Al but negatively with Mg. Silt and clay (SC) positively correlated with Al while negatively with Mg and pH at 5 cm. The MWD positively correlated with Ca and Mg. Soil pH and Mg also positively correlated with GMD at 15 cm while Al showed negative correlation. These findings suggest that practicing reduced tillage, combined with residue retention while observing proper cropping systems can markedly reduce the susceptibility of soil to erosion, improve soil organic carbon and increase soil microbial biomass.

Potassium Essential Nutrient Status and Management in Kenyan Soils for Increased Productivity

Kathuku-Gitonga A. N. — 2023-01-11

Nitrogen, phosphorus and potassium are regarded as the main basic nutrients necessary for plant growth and production and their functions are interrelated. Potassium is necessary for regulation of plant cells , for the production of proteins and enzymes. It improves crop’s disease and pests’ resistance, and it increases crop yield and plays a significant role in enhancing crop quality. Potassium deficiency inhibits protein production even when nitrogen is abundant. The objective of the study was to determine status of potassium in selected Kenyan soils and responses to applied potassium fertilizers. Studies were carried out in Kenya through laboratory soil analysis, meta-data analysis and fertilizer response studies. Soils were collected in the trial sites and analyzed using wet chemistry method. For meta-analysis, published materials were collected, collated, digitized and harmonized. Benefit cost ratios were calculated for each technology to ascertain its profitability. The soil analysis results showed that potassium, nitrogen, organic carbon and zinc were deficient. The meta-analysis results showed that, limited research studies had been conducted on potassium in Eastern, Coast and Rift Valley regions of Kenya. The most economical potassium responses were recorded under application of 60 kg K/ha, although the yields were not profitable. However, the fertilizer response studies showed increased crop yields on addition of potassium fertilizer up to 40 kg K/ha. Hence lower rates of potassium (less than or equal to 40 kg K/ha) are recommended to offset and maintain adequate potassium levels in the soil for optimal crop production and income. Nevertheless, soil analysis is key before any fertilizers are added to soils.

The Effect of Integrated Soil Fertility Management Practices on Bell Pepper Under Controlled Environmental Conditions

Morit C. H. — 2023-01-11

Continuous soil cultivation in tropical countries has resulted in depletion of nutrients that are essential for plant growth and development. Beside, adverse use of inorganic fertilizers has had implicating effects on availability of organic carbon, nutrients imbalance and deficiency, this over time has reduced production in horticultural crops. A study was conducted on bell pepper in a greenhouse to determine its response to different soil fertility management practices recorded by changes in plant height, number of fruits and weight, and crop yield. The experiment was set up at Nandi County. The treatments were laid out in randomized complete block design with four treatments; farmer Practice (25 t/ha organic manure), organic manure (50 t/ha), combined inorganic fertilizer (125 kg/ha 23:23:0 planting and 62.5 kg/ha 17:17:17 topdress) and organic manure (25 t/ha), and inorganic fertilizer (23:23:0) 250 kg/ha planting and 125 kg/ha 17:17:17 topdress. The results indicate that the treatments under organic manure recorded higher growth seen in the number of mean branches for organic manure -11.83, combined inorganic fertilizer -10.50, Farmer Practice -8.67, inorganic fertilizer -6.83 and plant height means for farmer Practice -53.8cm, organic manure -66.2cm, combined inorganic fertilizer -58.0cm, and inorganic fertilizer -44.2 cm. Yield was highest for the combined interaction of inorganic fertilizer and organic manure as seen on average number of fruits per plant for farmer Practice -24 fruits, organic manure -26 fruits, combined inorganic fertilizer -29 fruits and inorganic fertilizer -17 fruits and weight of fruits for farmer Practice -8.261, organic manure -9.083, combined inorganic fertilizer -9.611, inorganic fertilizer -6.539 kg). The results indicate that there is need to combine inorganic fertilizer and well decomposed organic manure for maximum yield of bell pepper. This should be done under greenhouse and other technologies where climatic conditions are controlled.

Innovative Approach of Predicting Soil Properties in The Eastern Slopes of Mount Kenya

Mutuma E. — 2023-01-11

The ever growing population and the need for more food make the knowledge of soil properties essential to maximise agricultural production on the currently available land. High costs of soil survey and laboratory measurements are among the major reasons for lack of sufficient soil information, which is important for proper land management. In this research, an innovative approach, comprising an optimized soil sampling design, a rapid and cost-efficient mid-infrared spectroscopy (MIR) and geostatistics was applied to provide necessary soil data for proper land management in the eastern slopes of Mt. Kenya. Conditional Latin hypercube method was used to develop a sampling design that ensured full coverage of environmental variables. Topographic variables were extracted from the digital elevation model, soil attributes from the Kenya Soil and Terrain (KENSOTER) database, and vegetation characteristics from the Normalized difference vegetation index generated from Landsat 8 imagery. The developed sampling scheme conserved the distribution of environmental covariates using box plots to validate. Soil spectra for the 232 samples collected from 77 georeferenced locations were measured using MIR spectroscopic methods at wavelength range of 4000 – 400/cm. To select the calibration samples from the MIR spectral database, principal component analysis and Kennard-Stone algorithm were used. Random forest regression was used to calibrate laboratory measurements to the soil MIR spectra. Good spectral prediction model performance was achieved as follows: soil organic carbon, total nitrogen and pH (R2 = 0.76, RMSE = 1.64; R2 = 0.81, RMSE = 0.09; R2 = 0.88 and RMSE = 0.48, respectively). Exchangeable Na, Mg, Al, K, Ca and extractable P were satisfactorily calibrated. Geostatistical analysis exhibited moderate spatial dependency of the soil properties. Soil properties were spatially predicted and mapped, and now can support targeted soil management decisions for different agricultural value chains.

Changes of Soil Conditions and Maize Yield After Years of Conventional or Reduced Tillage on a Mollic Andosol

Mwangi H.G. — 2023-01-11

Soil tillage affects soil physical, biological and nutrient cycling capacity. Field studies were conducted from 2016 to 2018 on same site using two tillage systems Conventional and Reduced tillage. Conventional tillage was done using a 3-disc plough while reduced tillage was done using a Chisel plough. The objective of this study was to evaluate changes in some soil properties induced by two different tillage treatments and their effect on maize grain yield. The trial was set at Kenya Agricultural Livestock & Research Organization (KALRO) Njoro on a Mollic Andosol. The design was randomised complete block replicated four times. The factor tillage had two levels. Changes in water stable aggregates, compaction as measured by changes in bulk density, soil water retention at pF 4.2, total soil organic carbon and hence soil organic matter, microbial biomass [bacteria and fungi] in form of total microbial biomass-N and microbial biomass-C and maize yield were obtained after three years in 2018. With exception of bulk density that was found to be higher in Conventional tillage, results showed that aggregate stability water stable aggregates, soil water retention capacity at pF4.2, soil organic matter. Total microbial biomass-nitrogen and microbial biomass-carbon were higher in reduced tillage. Maize grain yield was higher (p<0.05) in reduced tillage. Bulk density of the soil was observed to be higher after three years of conventional tillage compared to reduced tillage. Reduced tillage increased soil organic matter, structure, water retention and microbial biomass and maize yields. This study has revealed that reduced tillage is pivotal in healing the highly weathered soils that have become degraded and soil fertility has declined through decades of continuous disc and plough tillage, lengthy exploitation and nutrient mining leading to low crop yields.

Macro and Micro-Nutrient Status of Selected Kenya Soils

Omwakwe J. A. — 2023-01-11

Over the years there has been a decline in soil fertility in Kenya, which is responsible for low crop yields. Macro and micronutrients should be added to the soil as they ensure healthy produce by supplying the right balance of nutrients to the soil. Most farmers rely on nutrient recycling in their farms which is not sustainable as it leaves the soils depleted of nutrients. A study was therefore conducted to assess the limiting nutrients of soils in Coastal, Eastern, Rift Valley and Western parts of Kenya. Twenty-three soil samples (0 to 30 cm) from 13 counties were collected and evaluated for total nitrogen, total organic carbon, phosphorus, potassium, calcium, magnesium, manganese, copper, iron, zinc, sodium, electrical conductivity, cation exchange capacity (CEC), base saturation and soil pH. The mean values were 0.12%, 1.12, 19.09, 220.43, 1397.39, 163.98, 120, 52, 3.95, 52.78, 1.86, 92.80 mg/kg, 0.11mS/c, 11.98 Cmol (+)/kg, 83.13% and, 5.96, respectively. The soil analysis results indicated that nitrogen, phosphorous and zinc were deficient in most soils in Kenya. Nitrogen and carbon were positively correlated with each other (P≤ 0.01). Phosphorous on the other hand was negatively correlated with carbon and nitrogen. Zinc was negatively correlated with soil pH. The exchangeable bases showed significant correlation with each other. It was evident that the inadequate nutrients need to be considered and supplied for restoration of soil fertility and productivity.

Validation of Aquacrop Model for Simulated Climate Change Strategies for Maize Production in A Kenyan Nitisol

Onyango J.W. — 2023-01-11

Climate models predict temperature increases of between 3 -4o C in Africa by the end of the 21st Century; roughly 1.5oC higher than the global mean. AQUACROP model was validated to compare climate adaptation measures of irrigation, fertility and planting dates using maize crop. Data was collected in the two seasons of 2012 at Kabete in the Upper Midland agro-zone of Kenya from Climate Analogue Location in East and Southern Africa (CALESA) project. Long-term monthly rainfall, minimum and maximum temperatures data from Kabete Meteorological Station were used to determine trends while additional parameters were used to compute other model parameters. A scenario of 10% decline in rainfall and 3oC temperature increase led to at least 6 and 12% enhanced of biomass and yields respectively. Late planted crop suffered 0.3% reduction in canopy cover (CC), and 7.5% reduced transpiration hence 0.2% biomass. This probably resulted from disuse of initial moisture availability and nitrogen flush usually at rainfall onset. Application of 20 kg/ha of N enhanced transpiration hence biomass and especially grain yields by 24.7%. However, while 40kg/ha of N enhanced canopy cover, this did not lead to increased biomass and/or yields. It is purposeless to irrigate when rains are adequate since this only delays harvest index but does not enhance biomass or yields. Late planting is not recommended since the crop would suffer reduced transpiration, CC and biomass. It is needless to continusly enhance fertility levels beyond 20 kg/ha for maize at Kabete.

Enhancing The Efficacy of Biocontrols and Fungicide Application For Improved Late Blight Management and Yield of Potato

Kilonzi J.M. — 2023-01-11

Late blight (Phytophthora infestans), whose history dates back to 1840s, still remains a major constrain in potato production. Management of the disease solely depend on extensive use of fungicides that has been implicated, not only on their efficacy, but also has recently raised human health and biodiversity concern globally. Unexpectedly, proposed non-chemical disease management strategies including, use of biocontrols, are yet to yield substantive results that reflect effectiveness and cost saving. Therefore, field trial was conducted to optimize antifungal activities of Trichoderma asperellum and T. harzianum and Ridomil® application in managing potato blight. Seed was pre-treated with T. asperellum and T. harzianum suspensions at concentrations of 3 × 106, 7 × 106 and 1 × 107 CFU/mL and Ridomil® applied at spray intervals of 21, 14 and 7 days. Results revealed that, weather conditions contributed to late blight epidemics development and efficacy of the biocontrols and spray intervals. T. asperellum suppressed late blight more than T. harzianum. Concentration of the biocontrols had significant effect on late blight epidemics, growth and yield. Weekly fungicide application provided higher disease subdual and tuber yield than 14 and 21 days spray intervals. Use of biocontrols at concentration of 7 × 106 and 1 × 107 CFU mL-1 in combination with application of Ridomil® weekly and fortnightly, repressed blight effectively, contributed to higher yield and net farm income than any other combination. The results suggest that, integrated disease management using biocontrols and fungicide could delay late blight epidemics resulting in reduced fungicide application frequencies.