Effects of blended fertilizers on soil chemical properties of mature tea fields in Kenya

Volume06-2018
Advances in Agricultural Science 06 (2018), 04: 85-98

Effects of blended fertilizers on soil chemical properties of mature tea fields in Kenya

Kibet Sitienei 1, 3, 4*, Hellen W. Kamiri  2, Gilbert M. Nduru 1 and David M. Kamau 3

School of Natural Resources and Environmental Studies, Karatina University, P. O. Box 1957-10101, Karatina, Kenya.
School of Agriculture and Biotechnology, Karatina University, P. O. Box 1957-10101, Karatina, Kenya.
Kenya Agricultural and Livestock Research Organization (KALRO), P.O. Box 57811-00200, Nairobi, Kenya.
KALRO, Tea Research Institute, P. O. Box 820-20200, Kericho, Kenya.

ABSTRACT

Kenya tea industry have focused predominantly on the use of compound NPK fertilizers. These fertilizers cannot be easily manipulated for specific soils and tea clones. In this respect, two fertilizer blends contaning NPKS 25:5:5:4+9Ca+2.6Mg and NPKS 23:5:5:4 +10Ca+3Mg with trace elements have been produced commercially in the Country. However, their application rates that would result in optimal nutrients level are lacking. This is the knowledge gap that this study sought to address. Therefore, the fertilizer blends were assessed for their effects on soil chemical properties at different rate in two 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. Randomized complete block design (RCBD) were used to select 36 trial plots in the two areas which were treated with two fertilizer blends and standard NPK NPK 26:5:5 as control, and four fertilizer application rates (0 -control, 75, 150, and 225 kg N ha-1 yr-1). The trial was replicated three times. Soil samples were collected and analyzed for soil nutrient levels. The data were then subjected to the analysis of variance (ANOVA) using Mstat C computer software package. Soil acidity decreased significantly (P<0.05) down the profile (3.08, 4.02 and 4.08) in Kagochi. Soil available Ca and Mg levels were significantly (P<0.05) higher in the upper depth (Ca were 652 and 412 while Mg were 77 and 62 for Timbilil and Kagochi, respectively) in both sites then decreased down the profile. This study has shown that supplementing the soil applied NPK fertilizers with calcium, magnesium and micronutrients resulted in improved soil quality.

Keywords: Blended fertilizersClonal teaSeasons


How to Cite: Sitienei, K., Kamiri, H., Nduru, G., & Kamau, D. (2018). Effects of blended fertilizers on soil chemical properties of mature tea fields in Kenya. Advances in Agricultural Science6(4), 85-98.  

Introduction

Fertilizers are applied to fields to attain desired soil fertility levels for crops grown (Virk et al., 2013). The available nutrients content and their degree of accessibility and availability is very dynamic because of the various inorganic and biochemical processes in the soils (Baligar et al., 2001). These include temperature, water content, soil reaction, nutrient input, uptake and losses. Most of these nutrient forms (in solution, adsorbed, fixed, and sparingly soluble) are in a dynamic equilibrium. External applications only cause temporary changes in the relation between different fractions, but the basic nature of the equilibrium remains intact over time (Roy et al., 2006). A decrease in pH from the neutral range results in a smaller proportion of exchangeable Calcium (Ca) and Magnesium (Mg). In the case of phosphate, there is initially a greater mobilization of calcium phosphate, but later a strong immobilization or even fixation into aluminium and iron phosphates (Hansen et al., 2004). The dynamics of phosphate in soil present special problems because of the low solubility of most P compounds (Turner et al., 2006). The availability of some micronutrients, especially of Iron (Fe), Manganese (Mn) and Zinc (Zn), is increased strongly, and can even reach toxic levels (Roy et al., 2006). An increase in pH by liming can reverse the situation.  Nitrogen (N) is a critical nutrient for tea production (Zentner et al., 2003), but it is difficult to optimize nitrogen (N) fertilizer applications because of the dynamic nature over the growing season (Sitienei et al., 2013). Potassium is an important macronutrient for plants which, with N and P, plays an important role in plant development (Zhang et al., 2010). Among the major cations, K+ is absorbed by plants in the largest amount (Bahmanyar et al., 2010). Potassium deficiency results in a decrease in net photosynthetic rate and dramatic decrease in crop yield (Ding et al., 2006). The behavior of K in soil, release, absorption, fixation and leaching, is also strongly dependent on the clay content and types of clay minerals present (Sparks, 2000). The Sulphur (S) content of soils is usually lower than that of Ca or Mg (Roy et al., 2006). Calcium (Ca) is essential macronutrient for energy metabolism, photosynthesis, and membrane transport of plants (Takahashi and Anwar, 2007). An exchange complex dominated by Ca and adequately provided with Mg and K is a favourable precondition for good crop yields (Sato et al., 2009). Magnesium rate of release is too slow for optimal plant growth (Barlog and Grzebisz, 2001). Soil micronutrients are elements that are essential to plant growth, but are utilized in minimum quantities and may be harmful when added to the soils in high quantities (Bibiso et al, 2015). Micronutrient status in soils can be affected by long-term fertilization and intensive cropping (Ben-Yin et al., 2010). The main sources of micronutrients in plants are their growth media, agro inputs and soil (Saud and Oud, 2003). Plants take up the elements from the soil and under certain conditions, high levels can be accumulated in the leaves (Lasheen et al., 2008). Nutrient status is an unseen factor in plant growth, except when imbalances become so severe that visual symptoms appear on the plant (Flynn et al., 2004). Measurement of the fertility of an agricultural soil tells much about the productive potential. Fortunately, producers can control fertility by managing the plant’s nutritional status (Flynn et al., 2004). This study was meant to provide better insight on potential of blended fertilizers in providing required nutrition to tea crop.

 

Methodology

Study sites

The study was conducted at Tea Research Institute, Timbilil Estate in Kericho and KTDA, Kagochi farm in Nyeri; which represented the geographically different major tea growing regions in Kenya (East and West of the Great Rift Valley). Timbilil Tea Estate is located at 35° 21′ East longitude and 0° 22′ South latitude with altitude of 2200 m above the sea level. It has mean annual temperature and rainfall of 16.60C and 2175mm respectively. Kagochi Tea Farm is situated at an elevation of 2005 m above the sea level, latitude of 0° 25′ 43” South and longitude of 37° 7′ 41” East. It has mean annual temperature and rainfall of 15.40C and 2040mm respectively.

 

Variable determination

Variables used were three fertilizer types (one was control and four fertilizer application rates (one was control)

(a) Fertilizer types

  1. Blended NPKS 25:5:5:4+9Ca+2.6Mg + Trace Elements (TE) as Blend A
  2. Blended NPKS 23:5:5:4 +10Ca+3Mg + Trace Elements (TE) as Blend B

iii. Standard NPK 26:5:5 as control

(b) Fertilizer application rates (0 (control), 75, 150, and 225 kg N ha-1yr-1).

These fertilizers and composition are described in detail on Table 1.

Table 1. Fertilizer description, composition and application rates

Fertilizer description N composition (%) Physical properties pH Rate of application (Kg N ha-1 yr-1) Amount of fertilizer applied per bush (g/bush)
Ammoniacal Nitrate Amide Timbili estate Kagochi farm
Blended NPKS  A contains

25%N:5%P:5%K:4%S+9%Ca+2.6%Mg+ +B(140ppm)+ Zn(200ppm)+ Cu(89ppm)+ Mo(19ppm)

2 0 23 Mixture of white, black and brown granules 6.71+0.11 0 0 0
75 27.9 34.8
150 55.7 69.7
225 83.6 104.5
Blended NPKS  B contains

23%N:5%P:5%K:4%S +10%Ca+3%Mg+ B(140ppm)+ Zn(200ppm)+ Cu(89ppm)+ Mo(19ppm)

21 0 2 Mixture of white, black and brown granules 3.68+0.02 0 0 0
75 30.3 37.9
150 60.6 75.7
225 90.9 113.6
Standard NPK contains

26%N:5%P:5%K (control)

14 12 0 Grey uniform granules 3.73+0.01 0 0 0
75 26.8 33.5
150 53.6 67.0
225 80.4 100.5

 

Treatment application and management

The trial was set up on a field with 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 (7x12M) inclusive of net plot of 7*10M (70 plants) while in Kagochi, the plot size measured (8x8M) with a net plot of 7*8M (56 plants). The number of plants for effective sampling varied in the sites due to spacing. The fertilizer types were spread in rows as per characteristics and bush calculation based on spacing as shown on Table 1.

 

Soil sampling and analyses

In each plot, three core samples were randomly taken at each depth i.e. surface (0-15cm), sub surface (15-30cm) and bottom (40-60cm) using post hole soil auger and composited to provide the bulk sample of each depth. The samples were transferred to clearly labeled polythene bags and prepared for necessary analysis (Jackson, 1995). Soil pH were determined using procedure of Thomas (1996) (1:1 soil: water), then read using pH meter. The other parameters (Extractable phosphorus, potassium, calcium, magnesium and manganese and available trace elements (zinc, copper, boron, molybdenum, iron and aluminium) using Inductively Coupled Plasma Emission (ICPE) spectroscopy methods as outlined by Kalra (1998).

Data analysis

Effect of treatments application on soil properties data of mature tea fields with clone BBK 35 in Timbilil and TRFK 6/8 in Kagochi were subjected to the analysis of variance (ANOVA) using the Mstat C computer software package (Russel, 1995). The Least Significant Difference (LSD) procedure was then used to separate differences among the treatment means.

 

Results and discussion

Effect of fertilizer blends on soil chemical properties

Chemical soil analysis is routinely used in the determination of nutrients availability to plants (Kamau et al., 2006; Venkatesan et al., 2006). Thus, chemical analysis details the potential of plant nutrients in the soil (Kamau, 2008). The results of tea soil nutrient analysis after treatments application are shown Tables 1 and 2 and Figures 1 – 7 with their ANOVA in Tables 3 and 4.

 

Effect of the fertilizer blends on soil pH

The soil pH for the two sites is shown in Table 1. From the table, soil pH values were extremely acidic (3.55) in Kagochi to strongly acidic (4.86) in Timbilil. Kagochi site had a mean pH of 3.98 compared to 4.66 in Timbilil. The soil pH in Kagochi was below the lowest recommended pH level (pH of 4) for tea establishment and production (Kebeney et al., 2010). Initial mean pH measured were 3.31 and 3.56 before treatments in Kagochi and Timbilil respectively. The observed changes were expected since soil pH is influenced by many soil chemical parameters and may change seasonally depending on weather and the external inputs used ((Kamau, 2008)). Soil pH was not significantly influenced (P<0.05) by fertilizer type, application rates nor soil depth in Timbilil. Despite this, highest pH was observed with Blend “A” in both sites. However, the application rates and soil depth showed significant differences in Kagochi whereby the acidity increased with increase in N rates. This is corroborated by the Oh et al., (2006) findings that acidification rate usually increases with increasing N application. The decrease in soil pH with increase in N rate applied in tea soils has also been reported by Kebeney et al. (2010). This was expected considering the long term use of NPK fertilizers and especially for Kagochi where the soils are sandier (Sitienei et al., 2013). Another reason could be attributed to the decomposition of fallen tea leaves, which induced an increase of Al3+ in the soil thereby leading to soil acidification (Oh et al., 2006).

Soil acidity decreased significantly (P<0.05) down the profile (3.08, 4.02 and 4.08) in Kagochi.  Long term fertilizer trials in tea using NPKS 25:5:5:5 generally show a decrease in soil acidity down the soil profile due to leaching of the bases (Ca and Mg) from the acidic tea fertilizers (Owuor et al., 2011). However, the blended fertilizers contain Ca and Mg which countered the leaching effect hence the higher levels observed at the top soil. N fertilizers can have varying effects on soil pH. Nitrification (the conversion of NH4+ to NO3) and hydrolysis of NH4+ based fertilizers can decrease (acidify) soil pH due to the release of H+ ions to the soil solution. This reaction may have long-term effects on soil pH following years of application and may be beneficial in alkaline soils (Havlin et al., 2005). For the Mavuno blended fertilizers, the magnitude of acid-forming material reactions on pH are believed to be countered by calcium (Jones et al., 2002). Ca and Mg compounds are mainly used for the amelioration of acid soils. However, the effect of N fertilizers on pH should be considered on acidic soils. Ishibashi et al. (2004) have reported that nitrogenous fertilizers are known to produce H+ by the following reaction, which is induced by soil bacteria:

NH4+ + 2O2 → NO3+ H2O + 2H+

2NO2 + O2 =2NO3 (Leached)

Thus, during the application of these fertilizers to the soil, the rate of nitrification is reported to be higher and inorganic nitrogen may be rapidly converted to nitrate producing H+, which acidifies the soil (Yemane et al., 2008).

Table 2. Influence of fertilizer types, rates and depth on soil pH in Timbilil and Kagochi

Timbilil
 

 

 

 

Soil depth

Fertilizer type Blend “A” Blend “B” Standard NPK
Fertilizer Rate (kg N/ ha/year) 0 75 150 225 0 75 150 225 0 75 150 225
0-15cm 4.78 4.63 4.74 4.65 4.72 4.82 4.59 4.31 4.57 4.82 4.55 4.55
15-30cm 4.72 4.73 4.60 4.64 4.58 4.79 4.56 4.59 4.48 4.55 4.54 4.86
40-60cm 4.67 4.85 4.57 4.65 4.73 4.75 4.68 4.54 4.61 4.81 4.78 4.79
 

Kagochi

 

 

 

 

Soil depth

Fertilizer type Blend “A” Blend “B” Standard NPK
Fertilizer Rate (kg N/ ha/year) 0 75 150 225 0 75 150 225 0 75 150 225
0-15cm 4.04 4.29 3.73 3.60 3.86 3.92 3.65 3.84 3.90 3.89 3.78 3.55
15-30cm 4.18 4.34 3.99 3.78 4.03 4.13 3.83 4.07 4.04 4.11 3.94 3.74
40-60cm 4.20 4.38 4.03 4.00 4.10 4.16 4.03 4.09 4.07 4.12 4.03 3.79

 

Figure 1. Influence of fertilizer types, rates and soil depth on soil N

 

 

Figure 2. Influence of fertilizer types and rates on soil available phosphorus in Timbilil and Kagochi

 

Table 3. ANOVA of fertilizer types, rates and depth on some soil profile characteristics in Timbilil

Nutrient Type Rate Depth
pH CV (%)

LSD,P<0.05

7.65

NS

7.65

NS

4.28

NS

N (%) CV (%)

LSD,P<0.05

42.9

NS

42.9

NS

23.3

0.09

P (ppm) CV (%)

LSD,P<0.05

2.25

NS

2.25

0.90

2.52

1.80

K (ppm) CV (%)

LSD,P<0.05

19.3

NS

19.3

NS

15.4

40

Ca (ppm) CV (%)

LSD,P<0.05

5.45

NS

5.45

NS

8.79

148

Mg (ppm) CV (%)

LSD,P<0.05

7.53

NS

7.53

NS

10.47

18.13

Zn (ppm) CV (%)

LSD,P<0.05

10.1

NS

10.1

NS

45.3

NS

Cu (ppm) CV (%)

LSD,P<0.05

8.80

NS

8.80

NS

7.02

NS

 

Figure 3. Influence of fertilizer types, rates and soil depth on soil K

 

 

Table 4. ANOVA of fertilizer types, rates and depth on some soil profile characteristics in Kagochi

Nutrient Type Rate Depth
pH CV (%)

LSD,P<0.05

1.86

NS

1.86

0.12

7.50

0.03

N (%) CV (%)

LSD,P<0.05

50.9

NS

50.9

NS

47.6

0.09

P (ppm) CV (%)

LSD,P<0.05

65.2

NS

65.2

NS

80.9

4.62

K (ppm) CV (%)

LSD,P<0.05

6.09

NS

6.09

NS

6.10

33

Ca (ppm) CV (%)

LSD,P<0.05

28.4

NS

28.4

NS

34.2

29

Mg (ppm) CV (%)

LSD,P<0.05

23.6

5.71

23.6

NS

31.7

4.1

Zn (ppm) CV (%)

LSD,P<0.05

23.2

0.75

23.2

NS

19.7

NS

Cu (ppm) CV (%)

LSD,P<0.05

7.38

NS

7.38

NS

14.87

NS

 

Figure 4. Influence of fertilizer types, rates and soil depth on soil available calcium

 

 

Soil reaction is not a growth factor as such but it is a good indicator of several key determinants of growth factors, especially nutrient availability. Soil reaction greatly influences the availability of several plant nutrients. Most plants grow well in the neutral to slightly acid range of pH 6 to 7 with the dominant cation Ca. The preference of plants for a certain pH range is often determined by aspects of nutrient requirement and efficiency and not because of the pH as such. A decrease in pH from the neutral range results in a smaller proportion of exchangeable Ca and Mg. An increase in pH by liming can reverse the situation. In nature, there is a natural tendency towards soil acidification, the rate of which often increases under leaching, intensive cropping and persistent use of acid-forming fertilizers. Strong acidification leads to soil degradation. However, this can be overcome by the application of calcium carbonate (lime) or similar soil amendments.

 

Effect of the fertilizer blends on soil nitrogen

Figure 1 shows the influence of fertilizer types, rates and soil depth on total nitrogen. Total nitrogen in soil were not affected by fertilizer types and rates. Surface N were higher in Kagochi (0.841%) compared to Timbilil (0.597%). However, means for both sites (Timbilil, 0.531% and Kagochi,

Figure 5. Influence of fertilizer types, rates and soil depth on soil available magnesium

 

 

0.538%) were generally equal. The dynamics of N in soils are quite complex. Soil N is primarily in the organic fraction. As the bulk of the organic matter is in the upper horizons, most of the soil N is also in the topsoil as confirmed by this study (Roy et al., 2006).

 

Effect of the fertilizer blends on soil available phosphorus

The influence of fertilizer types, rates and soil depth at Timbilil and Kagochi is shown in Figure 2. Available P in Timbilil were much higher with a mean of 99.7 ppm compared to Kagochi with a site mean of 21.0 ppm. This might have arises from the different soil types and the higher P fixation for Kagochi soils associated with the lower pH (Table 1) as found by de la Paix Mupenzi et al. (2011). Fertilizer P efficiency depends more on soil fixation than on loss (Hanafi et al., 2002). Soil P more frequently precipitates as mineral complexes that decrease in solubility with time (Hopkins et al., 2008). Available phosphorus showed significant differences due to rates in Kagochi and soil depth in both sites. Phosphorus build up were observed in the upper soil depth of both sites. This confirmed observations made earlier by Kebeney et al. (2010). Most fertilizer trials on NPK 25:5:5 have not shown any influence of fertilizer rates on available P and

Figure 6. Influence of fertilizer types, rates and soil depth on soil available Zn

 

therefore the observed significance could arise from interactions of the additional nutrients with P in the blended fertilizers. The surface soils at Kagochi had much higher available P of 40 ppm compared to 12 ppm and 10 ppm of the lower profiles, respectively. The results were sufficient to high according to Adiloglu and Adiloglu (2006). This could be due to regular use of fertilizers. Phosphorus reaction has been shown to occur in acidic soils with Al, Fe, and Mn as the cations that combine with P (Hanafi et al., 2002). Ray and Mukhopadhyay (2012) found available P content (top soils) ranges of between 17.25 to 51.22 kg ha-1 in young, 19.22 to 56.73 kg ha-1 in medium and 12.56 to 56.73 kg ha-1 in old aged soils, respectively. Therefore, Timbilil soils had higher P content while Kagochi soils were within the reported ranges.

 

Effect of the fertilizer blends on soil potassium

Figure 3 shows the influence of fertilizer types, rates and soil depth on available potassium. From the figure, mean available potassium decreased significantly (P<0.05) with soil depth in both sites i.e. 455, 336 and 287 ppm and 360, 221 and 153 ppm in the three depths of Timbilil and Kagochi, respectively. These were sufficient to high levels according to Adiloglu and Adiloglu (2006) but in agreement with earlier findings by Ray and Mukhopadhyay (2012) who reported available K content (top soils) ranges of between 131 to 710 kg ha-1. This shows that leaching losses arising from the acidic soil conditions were minimal. Yemane et al. (2007) found that incorporation of tea prunings and addition of K fertilizers to the soils rapidly increases the concentration of available K that could be attributed to mineralization of the organic matter, the solubilization effect of rain water and due to increased chemical and biological fixation of potassium in the presence of fertilizers. Amount of K removed by plants depends on the production level, soil type, and the retention or removal of crop residues (Zhang et al., 2010).  Release and fixation rates of K in soil are highly dependent on the soil K balance, confirming that these are reversible processes that depend on plant uptake and fertilizer inputs (Simonsson et al., 2007). To meet the crop K requirement, non-exchangeable sources contributed on an average about 95% in the absence of applied K and 65% with added K (Lal et al., 2007).

Figure 7. Influence of fertilizer types, rates and soil depth on soil available copper

 

Effect of the fertilizer blends on calcium and magnesium

Figures 4 and 5 show the effects of fertilizer types, rates and soil depth on available calcium and magnesium. Mean available Ca and Mg levels for Timbilil and Kagochi are 523 ppm and 62.2 ppm and 302 ppm and 52.0 ppm, respectively. This indicates that the Timbilil soils have higher Ca and Mg levels and hence better buffered. The fertilizer rates did not influence the Ca and Mg levels in both sites. The blends had significantly (P<0.05) higher available Mg of 55.3 ppm and 55.7 ppm for Blends A and B, respectively compared to 45.1 ppm for the standard NPK in Kagochi. This could be attributed to the additional Mg content in the blends. Soil available Ca and Mg levels were significantly (P<0.05) higher in the upper depth (Ca were 652 and 412 while Mg were 77 and 62 for Timbilil and Kagochi, respectively) in both sites then decreased down the profile especially in Kagochi. The observed levels were deficient according to Adiloglu and Adiloglu (2006). The pattern was similar to the one for available soil potassium (Figure 4). The lower levels in Kagochi might be due to leaching of basic cations by the excessive rainfall observed in the area during the study (Ray and Mukhopadhyay, 2012).

 

Effect of the fertilizer blends on micronutrients (Zn and Cu)

Micronutrients are naturally present in soils (Nath, 2013). The influence of fertilizer types, rates and soil depth on available Zn and are shown in Figures 6 and 7.

In Kagochi blend “B” had significantly (P<0.05) lower Zn levels than blend “A” and NPK standard despite the blend containing Zn (Figure 6). In Timbilil there was no significant difference in types, rates and soil depth but some levels were in agreement with Nath (2013) findings and in sufficient to excess levels according to Adiloglu and Adiloglu (2006). Profile pattern were similar in both sites. The findings were different from earlier by Roy et al. (2006) which found increased availability of Zn at lower pH.

Copper levels were not influenced by fertilizer types, rates and soil depth (Figure 7) despite its presence in the blends, implying that copper may not be limiting in the sites. However, the levels were higher in Kagochi than Timbilil and therefore in agreement with earlier findings by Roy et al. (2006) which showed increased availability of Cu at lower pH. The Cu levels were lower than what Nath found in 2013 but in excess according to Adiloglu and Adiloglu (2006).

 

Conclusion

This study has shown that supplementing the soil applied NPK fertilizers with calcium, magnesium and micronutrients resulted in improved soil quality. The calcium and magnesium in the blends also contributed to the stabilization of soil acidity, which is desirable for tea cultivation. Soil acidity decreased significantly (P<0.05) down the profile (3.08, 4.02 and 4.08) in Kagochi. Soil available Ca and Mg levels were significantly (P<0.05) higher in the upper depth in both sites (Ca were 652 and 412 while Mg were 77 and 62 for Timbilil and Kagochi, respectively) then decreased down the profile.

 

Acknowledgements

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.

 

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