Kenya’s tea industry depends predominantly on imported compound NPK fertilizers to replenish nutrients removed through plucking. These fertilizers cannot be easily manipulated for specific soils and tea clones. They also frequently become hazardous within tea-growing environments. In this respect, two fertilizer blends containing NPKS 25 : 5 : 5 : 4 + 9Ca + 2.62Mg and NPKS 23 : 5 : 5 : 4 + 10Ca + 3Mg with trace elements have been produced commercially in the country. However, the extent to which the blended fertilizers may contribute to optimal economic gains without degrading the environment has not been determined. This was the knowledge gap that this study seeks to address. The goal of this study was to evaluate the economic efficacy of fertilizer blends with the aim of identifying optimal levels of application which would maximize tea productivity with minimal negative impacts on the environment. The study hypothesized that blended fertilizers maximize productivity of tea clones with minimal environmental damage. The fertilizer blends were evaluated in two study sites, i.e., Timbilil Estate in Kericho and Kagochi farm in Nyeri. The sites were selected purposefully, one in the eastern and the other in the western tea-growing areas. The trial was laid out in randomized complete block design with two fertilizer blends and the standard NPK 26 : 5 : 5 as control. The treatments were applied at four fertilizer rates (0 (control), 75, 150, and 225 kg·N·ha−1·yr−1), replicated thrice. Leaf samples were collected and analyzed for nutrient uptake as well as associated yields and economic trends. The economic optimum nitrogen rate (EONR) was achieved at 75 kg·N·ha−1·yr−1 at Kagochi with all fertilizers, while at Timbilil, EONR was variable, between 75 and 225 kg·N·ha−1·yr−1 with fertilizer types. This study has shown that, based on the economic point of view, Blend “A” was the most efficient and consistent fertilizer in production and economic returns across the two sites.
Tea is a major cash crop whose sustained productivity is highly desired by all stakeholders in its value chain. Nutrient requirements for commercial tea production are particularly high because the pluckable portions contain the largest percentage of nutrients in the plant [
Chemical fertilizers with ability to replenish depleted nutrients in optimum quantities and forms have been recognized as an important component of sustainable soil fertility management [
Soil nutrients availability, their content, and degree of accessibility are very dynamic because of the various inorganic and biochemical processes in the soils [
Fertilizer recommendations are based on field input trials and their effects on crop yield (yield responses) in both agronomic and economic terms [
The trial was established using a factorial randomized completely block design (RCBD) with three fertilizer types (one is control) and four fertilizer application rates (one is control) replicated three times. The randomized complete block design (RCBD) is a standard design for agricultural experiments in which similar experimental units are grouped into blocks or replicates [
The trial was set using clone BBK 35 in Timbilil planted in 1988 at a spacing of 4 × 2.5 ft. and clone TRFK 6/8 in Kagochi planted in 1965 at a spacing of 5 × 2.5 ft. The plot size in Timbilil measured (7 × 12 M) inclusive of a net plot of 7 ∗ 10 M (70 plants), while in Kagochi, the plot size measured (8 × 8 M) with a net plot of 7 ∗ 8 M (56 plants). Variables used were three fertilizer types (one was control) and four fertilizer application rates (one was control). Fertilizer types: Blended NPKS 25 : 5 : 5 : 4 + 9Ca + 2.6Mg + trace elements (TE) as Blend A Blended NPKS 23 : 5 : 5 : 4 + 10Ca + 3Mg + trace elements (TE) as Blend B Standard NPK 26 : 5 : 5 as control Fertilizer application rates (0 (control), 75, 150, and 225 kg·N·ha−1·yr−1)
The fertilizer types were spread in rows as per characteristics and bush calculation based on spacing.
The areas receive the bimodal type of rainfall with peaks in April to May and October to November. Total annual precipitation in Timbilil estate is 2175 mm, while in Kangaita, annual rainfall is about 2040 mm. Temperature ranges from 12 to 20°C in Kangaita and 14 to 19°C in Timbilil.
Leaf samples (approximately 100 g of two leaves and a bud and mature leaf) were plucked in each plot and taken to laboratory. The samples were oven-dried at a temperature of 105°C for 72 hours before milling. Total nitrogen in the leaves was determined by the Kjeldahl method [
Yield components of tea are described as the number of plucked shoots per unit land area and the mean weight per shoot [
Effect of treatments application on mean yields and leaf nutrients uptake data of mature tea clone BBK 35 in Timbilil and TRFK 6/8 in Kagochi was subjected to the analysis of variance (ANOVA) using the MSTAT C computer software package [
An estimated nutrient balance (inputs and outputs) was calculated by assuming that (i) soils existing nutritional status was minimal (ii) over the short-term, there were no nutrients recycled as plant prunings, and (iii) the amount of nutrients sequestered in the standing crop was generally small [
Economic appraisal of the blended fertilizers was determined using two simple approaches: productivity change approach (PCA) and replacement cost approach (RCA) [
For the productivity change approach, a function that stipulates a technical relationship between inputs and outputs was used. Market conditions and policy distortions affecting production decisions were taken into account [ One (1) kg made tea is equivalent to 4 kg green leaves (GL) Cost of plucking is average of KSh. 9 per kg GL Cost of leaf collection and processing per kg made tea is KSh. 100 Cost of pruning and tipping is estimated at KSh. 4 per bush of a third of the farm per year Cost of weeding is one man-day per two months (or six man-days in a year) Average price of made tea per kg is KSh. 250 Cost of fertilizers is KSh. 2,150 and KSh. 2,300 per 50 kg fertilizer bag for compound and blended, respectively
The replacement cost approach (RCA) focuses on the additional input required to compensate for lost soil nutrients. Replenishment models were calculated only for the lost nutrient or the negative net nutrient balance bearing in mind that The nutrients can either be a limiting factor for growth or not Available nutrients are supposed to replace, in part, nonavailable nutrients Fertilizer efficiency is assumed Likely side-effects of large fertilizer applications on micronutrient availability and soil acidity
Nutrient pools measured in this study were total N, P2O5, and K2O in harvested tea. Nutrient inputs were mainly from applied fertilizers. Other sources and losses were not determined in this study due to limitations of time and resources. Tables
Apparent nutrient budget of Blend A (NPKS 25 : 5 : 5 : 4 + 9Ca + 2.6Mg + trace elements) in Timbilil and Kagochi.
Site | NPK input as fertilizer (kg·ha−1) | Yield (kg·Mt·ha−1·yr−1) | Mean NPK content in 2L + B (%) | Gross NPK removed through harvest (kg·ha−1) | Nutrient budget (input as fertilizer and output as harvest) (kg·ha−1) | ||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|
N | P2O5 | K2O | N | P | K | N | P2O5 | K2O | N | P2O5 | K2O | ||
Timbilil | 0 | 0 | 0 | 2052 | 4.67 | 0.466 | 2.15 | 96 | 23 | 53 | −96 | −23 | −53 |
75 | 15 | 15 | 2532 | 4.84 | 0.478 | 2.29 | 123 | 27 | 70 | −48 | −12 | −55 | |
150 | 30 | 30 | 2683 | 4.97 | 0.48 | 2.31 | 133 | 30 | 75 | 17 | 0 | −45 | |
225 | 45 | 45 | 2995 | 4.86 | 0.509 | 2.41 | 146 | 34 | 87 | 79 | 11 | −42 | |
|
|||||||||||||
Kagochi | 0 | 0 | 0 | 1654 | 4.53 | 0.497 | 2.32 | 77 | 18 | 46 | −77 | −18 | −46 |
75 | 15 | 15 | 1975 | 4.44 | 0.482 | 2.36 | 96 | 23 | 57 | −21 | −8 | −42 | |
150 | 30 | 30 | 1808 | 4.54 | 0.454 | 2.26 | 90 | 18 | 49 | 60 | 12 | −19 | |
225 | 45 | 45 | 1795 | 4.61 | 0.457 | 2.27 | 87 | 18 | 49 | 138 | 27 | −4 |
“−” denotes a negative value.
Apparent nutrient budget of Blend B (NPKS 23 : 5 : 5 : 4 + 10Ca + 3Mg + trace elements) in Timbilil and Kagochi.
Site | NPK input as fertilizer (kg·ha−1) | Yield (kg·MT·ha−1·yr−1) | Mean NPK content in 2L + B (%) | Gross NPK removed through harvest (kg·ha−1) | Nutrient budget (input as fertilizer and output as harvest) (kg·ha−1) | ||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|
N | P2O5 | K2O | N | P | K | N | P2O5 | K2O | N | P2O5 | K2O | ||
Timbilil | 0 | 0 | 0 | 2140 | 4.67 | 0.466 | 2.15 | 100 | 23 | 55 | −100 | −23 | −55 |
75 | 15 | 15 | 2336 | 4.84 | 0.478 | 2.29 | 113 | 25 | 64 | −38 | −9 | −48 | |
150 | 30 | 30 | 2816 | 4.97 | 0.48 | 2.31 | 140 | 32 | 78 | 10 | 1 | −45 | |
225 | 45 | 45 | 2854 | 4.86 | 0.509 | 2.41 | 139 | 34 | 83 | 86 | 15 | −34 | |
|
|||||||||||||
Kagochi | 0 | 0 | 0 | 1420 | 4.53 | 0.497 | 2.32 | 66 | 16 | 40 | −66 | −16 | −40 |
75 | 15 | 15 | 1870 | 4.44 | 0.482 | 2.36 | 91 | 21 | 53 | −16 | −5 | −37 | |
150 | 30 | 30 | 1859 | 4.54 | 0.454 | 2.26 | 92 | 18 | 51 | 58 | 15 | −18 | |
225 | 45 | 45 | 1742 | 4.61 | 0.457 | 2.27 | 85 | 18 | 48 | 140 | 31 | 1 |
“−” denotes a negative value.
Apparent nutrient budget of standard NPK in Timbilil and Kagochi.
Site | NPK input as fertilizer (kg·ha−1) | Yield (kg·Mt·ha−1·yr−1) | Mean NPK content in 2L + B (%) | Gross NPK removed through harvest (kg·ha−1) | Nutrient budget (input as fertilizer and output as harvest) (kg·ha−1) | ||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|
N | P2O5 | K2O | N | P | K | N | P2O5 | K2O | N | P2O5 | K2O | ||
Timbilil | 0 | 0 | 0 | 2132 | 4.67 | 0.466 | 2.15 | 100 | 23 | 55 | −100 | −23 | −55 |
75 | 15 | 15 | 2329 | 4.84 | 0.478 | 2.29 | 113 | 25 | 64 | −38 | −11 | −50 | |
150 | 30 | 30 | 2679 | 4.97 | 0.48 | 2.31 | 133 | 30 | 75 | 17 | −1 | −46 | |
225 | 45 | 45 | 3099 | 4.86 | 0.509 | 2.41 | 151 | 37 | 90 | 74 | 6 | −47 | |
|
|||||||||||||
Kagochi | 0 | 0 | 0 | 1683 | 4.53 | 0.497 | 2.32 | 79 | 18 | 47 | −79 | −18 | −47 |
75 | 15 | 15 | 1781 | 4.44 | 0.482 | 2.36 | 86 | 21 | 51 | −11 | −7 | −37 | |
150 | 30 | 30 | 1810 | 4.54 | 0.454 | 2.26 | 90 | 18 | 49 | 60 | 11 | −20 | |
225 | 45 | 45 | 1800 | 4.61 | 0.457 | 2.27 | 87 | 18 | 49 | 138 | 25 | −6 |
“−” denotes a negative value.
Estimation of nutrient budgets showed that fertilizer Blend A when applied at the rate of 0 and 75 kg·N·ha−1·yr−1 resulted in negative nitrogen balances of 96 and 48 kg·ha−1, respectively, in Timbilil. In Kagochi, N budgets for 0 rate were 77 kg·ha−1 and 21 kg·ha−1 for the 75 kg·N·ha−1·yr−1 rate. Fertilizer rates of 150 and 225 (kg·N·ha−1·yr−1) showed positive N balances of 17 and 79 kg·ha−1, respectively, in Timbilil and 60 and 138 kg·ha−1 in Kagochi as shown in Table
Fertilizer Blend B showed negative apparent nutrient budgets in N, P2O5, and K2O at rates of 0 and 75 kg·N·ha−1·yr−1 in both sites. However, the last N rates of 150 and 225 kg·N·ha−1·yr−1 resulted in negative K2O balances of 45 and 38 kg·ha−1, respectively, in Timbilil (Table
Apparent nutrient budgets for the standard tea fertilizer resulted in negative P2O5 balances of 23, 11, and 1 kg·ha−1 in Timbilil when applied at rates of 0, 75, and 150 kg·N·ha−1·yr−1, respectively (Table
From these findings, it was observed that, within the margin of error, the third rate for all the fertilizer types in Timbilil was almost in equilibrium. The same equilibrium was observed by Sitienei and Kamau [
Nitrogen is the most dynamic nutrient and after transformation, can move in the atmosphere, as well as in aquatic systems. The amounts of nitrogen (N) involved in transfers through trade are ecologically significant especially when the 2020 projections are considered. Potassium and phosphorus transfers are also significant and may provide opportunities for the eventual recycling of the important nutrients, especially given the high cost of potassium mining and transportation [
The valuation of benefit or loss in money was in terms of the amount saved due to increased nutrient status or amount to be incurred for increasing the nutrient status, respectively [
The method involves a two-step procedure. Firstly, the physical effects of changes in the environment on productive activity are determined, i.e., the value of productivity change is equal to the difference in crop yields with and without that nutrient change. The second step consists of valuing the resulting changes in production, usually using market prices. In this case, the PCA takes the reduction in the capitalized net annual income stream gained through agricultural production (i.e., loss of income through crop yields) as a substitute for the costs of nutrient depletion.
The profitability of the three fertilizers under study was analyzed in Tables
Economic evaluation of fertilizer Blend A application in Timbilil and Kagochi.
Site |
|
Bags of NPK(S) ha−1 required | Total cost of fertilizer at KSh. 2,300/bag of 50 kg | kg·Mt·ha−1·yr−1 (TPP) | Production in kg of GL·ha−1·yr−1 | Cost of plucking (KSh) | Cost of pruning (KSh) | Cost of weeding (KSh) | Cost of collection and processing (KSh) | Gross earnings from made tea ha−1·yr−1 (KSh) | Total cost of production (KSh) | Gross profit ha−1·yr−1 (KSh) | Average physical product (APP) | Marginal physical product (MPP) |
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Timbilil | 0 | 0 | 0 | 2052 | 8,208 | 73,872 | 14355 | 4125 | 205,200 | 513,000 | 297,552 | 215,448 | 0 | 0 |
75 | 6 | 13,800 | 2532 | 10,128 | 91,152 | 14355 | 4125 | 253,200 | 633,000 | 376,632 | 256,368 | 422 | 80 | |
150 | 12 | 27,600 | 2683 | 10,732 | 96,588 | 14355 | 4125 | 268,300 | 670,750 | 410,968 | 259,782 | 224 | 25 | |
225 | 18 | 41,400 | 2995 | 11,980 | 107,820 | 14355 | 4125 | 299,500 | 748,750 | 467,200 | 281,550 | 166 | 52 | |
|
||||||||||||||
Kagochi | 0 | 0 | 0 | 1654 | 6,616 | 59,544 | 14355 | 4125 | 165,400 | 413,500 | 243,424 | 170,076 | 0 | 0 |
75 | 6 | 13,800 | 1975 | 7,900 | 71,100 | 14355 | 4125 | 197,500 | 493,750 | 300,880 | 192,870 | 329 | 54 | |
150 | 12 | 27,600 | 1808 | 7,232 | 65,088 | 14355 | 4125 | 180,800 | 452,000 | 291,968 | 160,032 | 151 | −28 | |
225 | 18 | 41,400 | 1795 | 7,180 | 64,620 | 14355 | 4125 | 179,500 | 448,750 | 304,000 | 144,750 | 100 | −2 |
TPP: total physical product, GL: green leaf, MPP: marginal physical product, and APP: average physical product.
Economic evaluation of fertilizer Blend B application Timbilil and Kagochi sites.
Site | N rates in kg·ha−1 | Bags of NPK(S) ha−1 required | Total cost of fertilizer at KSh 2,300/bag of 50 kg | kg·Mt·ha−1·yr−1 (TPP) | Production in kg of GL·ha−1·yr−1 | Cost of plucking (KSh) | Cost of pruning (KSh) | Cost of weeding (KSh) | Cost of collection and processing (KSh) | Gross earnings from made tea ha−1·yr−1 (KSh) | Total cost of production (KSh) | Gross profit ha−1·yr−1 (KSh) | Average physical product (APP) | Marginal physical product (MPP) |
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Timbilil | 0 | 0 | 0 | 2140 | 8,560 | 77,040 | 14355 | 4125 | 214,000 | 535,000 | 309,520 | 225,480 | 0 | 0 |
75 | 6 | 13,800 | 2336 | 9,344 | 84,096 | 14355 | 4125 | 233,600 | 584,000 | 349,976 | 234,024 | 389 | 33 | |
150 | 12 | 27,600 | 2816 | 11,264 | 101,376 | 14355 | 4125 | 281,600 | 704,000 | 429,056 | 274,944 | 235 | 80 | |
225 | 18 | 41,400 | 2854 | 11,416 | 102,744 | 14355 | 4125 | 285,400 | 713,500 | 448,024 | 265,476 | 159 | 6 | |
|
||||||||||||||
Kagochi | 0 | 0 | 0 | 1420 | 5,680 | 51,120 | 14355 | 4125 | 142,000 | 355,000 | 211,600 | 143,400 | 0 | 0 |
75 | 6 | 13,800 | 1870 | 7,480 | 67,320 | 14355 | 4125 | 187,000 | 467,500 | 286,600 | 180,900 | 312 | 75 | |
150 | 12 | 27,600 | 1859 | 7,436 | 66,924 | 14355 | 4125 | 185,900 | 464,750 | 298,904 | 165,846 | 155 | −2 | |
225 | 18 | 41,400 | 1742 | 6,968 | 62,712 | 14355 | 4125 | 174,200 | 435,500 | 296,792 | 138,708 | 97 | −20 |
“−” denotes a negative value.
Economic evaluation of standard NPK applied to tea in Timbilil and Kagochi.
Site | N rates in kg·ha−1 | Bags of NPK(S) ha−1 required | Total cost of fertilizer at KSh 2,300/bag of 50 kg | kg·Mt·ha−1·yr−1 (TPP) | Production in kg of GL·ha−1·yr−1 | Cost of plucking (KSh) | Cost of pruning (KSh) | Cost of weeding (KSh) | Cost of collection and processing (KSh) | Gross earnings from made tea ha−1·yr−1 (KSh) | Total cost of production (KSh) | Gross profit ha−1·yr−1 (KSh) | Average physical product (APP) | Marginal physical product (MPP) |
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Timbilil | 0 | 0 | 0 | 2132 | 8,528 | 76,752 | 14355 | 4125 | 213,200 | 533,000 | 308,432 | 224,568 | 0 | 0 |
75 | 5.8 | 12,470 | 2329 | 9,316 | 83,844 | 14355 | 4125 | 232,900 | 582,250 | 347,694 | 234,556 | 402 | 34 | |
150 | 11.5 | 24,725 | 2679 | 10,716 | 96,444 | 14355 | 4125 | 267,900 | 669,750 | 407,549 | 262,201 | 233 | 61 | |
225 | 17.3 | 37,195 | 3099 | 12,396 | 111,564 | 14355 | 4125 | 309,900 | 774,750 | 477,139 | 297,611 | 179 | 72 | |
|
||||||||||||||
Kagochi | 0 | 0 | 0 | 1683 | 6,732 | 60,588 | 14355 | 4125 | 168,300 | 420,750 | 247,368 | 173,382 | 0 | 0 |
75 | 5.8 | 12,470 | 1781 | 7,124 | 64,116 | 14355 | 4125 | 178,100 | 445,250 | 273,166 | 172,084 | 307 | 17 | |
150 | 11.5 | 24,725 | 1810 | 7,240 | 65,160 | 14355 | 4125 | 181,000 | 452,500 | 289,365 | 163,135 | 157 | 5 | |
225 | 17.3 | 37,195 | 1800 | 7,200 | 64,800 | 14355 | 4125 | 180,000 | 450,000 | 300,475 | 149,525 | 104 | −2 |
“−” denotes a negative value.
Profitable rates fluctuated among the rates of the three fertilizers in the two sites. In Timbilil, profitable rates were 225 kg·N·ha−1 for Blend A at KSh. 281,550 per hectare per year (Table
In Kagochi, the fertilizer rate of 75 kg·N·ha−1 was the most profitable for all the three fertilizers (192,870, 180,900, 172,084 KSh.·ha−1·yr−1 for Blend A, Blend B, and NPK standard (Tables
These findings are consistent with those by Njogu et al. [
In the economic analysis studies, the economic optimum rate and the most profitable rate for each fertilizer in each site were determined. The economic optimum nitrogen rate (EONR) is realized when the cost of the last increment of additional N equals the value of tea yield increase. Tables For Blend A, the EONR was achieved at 6 bags of fertilizer per hectare per year at both Timbilil and Kagochi For Blend B, the EONR was achieved at 13 and 6.5 bags of fertilizer per hectare per year in Timbilil and Kagochi, respectively For the standard NPK, the EONR was achieved at 19.6 and 5.8 bags of fertilizer per hectare per year in Timbilil and Kagochi, respectively Kagochi had the least fertilizer requirement across all the fertilizer types
The magnitude of the increase in yield tended to diminish as the total level of nitrogen rate increased. As successive units of fertilizer were added to other costs, it reached a point where the value of the marginal product was less than the unit cost of N used to produce it. The economic implication of this trend is that the value of the additional crop at first exceeded the cost of applying fertilizer but eventually only marginal additional crop was obtained for each unit of additional fertilizer resulting in no achievement of monetary gain. A fertilizer type may do well agronomically but poorly in economic terms as a result of low commodity prices or high production costs.
With higher N prices, it becomes more important to fertilize at the most economic rate, which may differ from the agronomic rate. Kiprono et al. [
The most economic fertilizer rate for fertilizer Blend A was 75 kg·N·ha−1·yr−1 for both sites. However, economic rates were different for Blend B and standard NPK in Timbilil and Kagochi. This shows that fertilizer recommendations vary widely for different tea-growing regions depending on the age of the bushes, pruning cycle, yield, and soil fertility as was found by Tshivhandekano et al. [
The findings here are in agreement with earlier findings that farming should be economically sustainable so that it can contribute to the economic security of key factors in the farm and in the food system as a whole [
Figures
Soil nutrient replenishment model for Timbilil.
Soil nutrient replenishment model for Kagochi.
According to the results, it was confirmed that the replenishment model for Timbilil was linear while that of Kagochi was polynomial. In Timbilil, the mean soil replenishment model for the different fertilizer types was given by the following equation:
This shows that the amount of NPK fertilizer required to restock the soil was higher than applied N and it increased linearly with the N rates.
In Kagochi, the mean replenishment model was given by the following equation:
The model showed that the amount of input required increased initially up to 75 kg·N·ha−1·yr−1 then decreased with the N rates.
The models showed that replenishment is vital if tea productivity is to be sustained. The nutrient balance model proved to be a useful indicator of nutrient depletion and offers a biophysical base for its economic assessment via the replacement cost approach (RCA). Nutrients export from land with no capacity to replenish those nutrients represents long-term stripping of soil stocks, exposing developing countries to significant long-term risk of soil productive failure [
Researchers have shown that nutrient losses due to uptake by crops, erosion, leaching, and N volatilization are only partially compensated by crop residues left on the field, manure and fertilizer application, and atmospheric inputs; thus, the annual NPK balances for sub-Saharan Africa are negative with minus 22–26 kg·N, 6-7 kg P2O5, and 18–23 kg·K2O·ha−1 [
The models like the NUTMON approach have been developed completely at the farm level. This means that they can also serve as tools for monitoring nutrient flows on farms [
As hypothesized, blended fertilizers were found to be capable of increasing productivity while conserving the environment. The positive findings lead to sustainable farming where productivity is raised with minimum negative impacts on the environment and also help in recovering already degraded soil [
The ultimate aim of this study was to optimize tea production, maximize positive interactions, maximize net returns, minimize the depletion of soil nutrients, and minimize nutrient losses or negative impact on the environment. As hypothesized, blended fertilizers were found to be capable of increasing productivity while conserving the environment. The positive findings could lead to sustainable farming where productivity is raised with minimum negative impacts on the environment and also help in recovering already degraded soil. From an economic point of view, Blend A was the most efficient and consistent fertilizer in production, economic returns, and its environmental effects across the two sites.
The data used to support the findings of this study are available from the corresponding author upon request.
The authors declare that they have no conflicts of interest.
The authors are very grateful to Athi River Mining Ltd., KALRO Tea Research Institute, and KTDA for funding the research and Karatina University for providing technical support during the process of data collection.