Joint proceedings of the 27th Soil Science Society of East Africa and the 6th African Soil Science Society

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1 Soil fertility status, quality of available manure and its implication on soil fertility maintenance in the peri-urban areas of semi-arid eastern Kenya Abstract J.K. Itabari, D.M.G.Njarui and P. Kathuli Kenya Agricultural Research Institute, Katumani, P.O. Box Machakos, Kenya, A study of nutrient status of cropland soils and the quality of farmyard manure applied on the farms was undertaken in the peri-urban areas of Wote town in Makueni County and Wamunyu market in Machakos County in semi-arid eastern Kenya. The objective of the study was to recommend appropriate soil fertility maintenance strategies for enhancing productivity of vegetables and fodder crops in crop-livestock production systems in the two peri-urban areas. Soil and manure samples were collected from 54 farms in the two areas and analysed at the National Agricultural Research Laboratories, Nairobi. Results of soil analysis indicated that with the exception of nitrogen, phosphorus, organic carbon and zinc, the other nutrient elements analyzed for were above critical levels. Results of manure analysis indicated that with the exception of nitrogen, phosphorus and zinc, the other nutrient elements analyzed for were above critical levels. It was concluded that due to the low levels of nitrogen (< 2% N) in the farmyard manure and the insufficient quantities available on farm, application of manure alone cannot maintain soil fertility for sustainable crop and livestock production. It was, therefore, recommended that the available quantities of farmyard manure should be augmented with inorganic nitrogen fertilizers. Intensification of legume production in order to increase N pool in the soil, through N 2-fixation, was also recommended. Keywords: semi-arid areas, peri-urban, farmyard manure, soil fertility, nutrients. Introduction There has been increased land pressure in the semi-arid lands of Kenya due to the rapid increase in population, brought about by high population growth and influx of people from the high potential areas in search of new farmlands. This has led to intensive land use without adequate replenishment of nutrients, resulting in the depletion of soil nutrients, hence the decline in soil fertility. In most of these areas, the soils have low organic matter content and are deficient in nitrogen (N) and phosphorus (P) (Nadar and Faught, 1984; Ikombo, 1984; Okalebo et al., 1992; Okalebo et al., 1996; Okwach et al., 1999; Gachimbi et al., 2005; De Jager et al., 2005). The outflow of nutrients in most farms exceeds input flows (Smaling et al., 1993; Gachene et al., 2000; Gachimbi et al., 2005; De Jager et al., 2005). Organic matter depletion affects soil behaviour physically and chemically by causing loss of water-stable structure and reduced water conductivity, which are manifested as slaking of cultivated seedbeds, reduced infiltration rates and increased proportion of rain lost as runoff (McCown and Jones, 1992). Thus, increasing soil fertility requires increasing soil carbon, N and P. Farmyard manure is the principal source of nutrients for crop and fodder production in these areas. Its use is also the main method of recycling nutrients and, where animals have access to forage outside the farm, a means of collecting nutrients from surrounding areas. Manure is the best amendment for increasing soil fertility as it provides carbon, prevents acidification and generally provides the balance of all nutrients (Pichot et al., 1981; Nambiar and Abrol, 1989, cited by McCown and Jones, 1992). A survey of nutrient status of cropland soils and the quality of FYM applied on the farms was undertaken in the peri-urban areas of Wote town in Makueni County and Wamunyu market in Machakos County in semi-arid Eastern Kenya, where farmers are engaged in dairy and vegetable production, with the aim of recommending appropriate soil fertility maintenance strategies for enhancing the productivity of these enterprises October Nakuru, Kenya.

2 Materials and methods Study areas The study was conducted in the peri-urban areas of Wote town in Makueni County and Wamunyu market in Machakos County. Wote town is the main urban centre in Makueni County while Wamunyu market is one of the fast-growing urban centres in Machakos County and is 40 km southeast of Machakos town along Machakos-Kitui road. Wote town is in the transition zone between Lower Midlands (LM) 4 and 5 at 1100 m. Wamunyu market is in LM 4 at 1190 m (Jaetzold et al., 2006). The two areas have a bimodal rainfall pattern, which is almost evenly distributed between the long rains (March-May) with a peak in April, and the short rains (October-December) with a peak in November. The main soil types in the two areas are Cambisols and Ferralsols (Jaetzold and Schmidt, 1983). The farms from where the soil and manure samples were collected were within 15 km radius of the two urban centres. These farms had been selected earlier for a baseline survey of a crop-livestock integration project using a purposive sampling procedure, where the main criterion was possession of at least one cross breed or high grade dairy animal. Soil sampling, collection of manure samples and analysis Soil sampling and collection of manure samples were undertaken in April Soil samples were taken from the 0-30 cm layer from 24 farms in Wamunyu area and 30 farms in Wote area. On each farm, soil sampling was carried out only on the terraces where farmers indicated they intended to grow vegetables and fodder. At least 5 samples were randomly taken in each terrace, composited and then sub-sampled. One manure sample was also collected from each farm and together with the soil samples analysed at KARI-Kabete. Complete analyses were carried out for soil and manure samples. In soil analysis, total N was determined by the Kjeldahl method (Hinga et al., 1980). Organic carbon by calorimetric method, Soil ph was determined in a 1:1 (w/v) soil-water suspension with a ph meter. Phosphorus, potassium, calcium, magnesium and manganese were determined by the Mehlich Double Acid method (Hinga et al., 1980). Copper, iron and zinc were determined by Atomic Absorption Spectrophotometer (AAS). For manure analysis, the samples were determined by the digestion method where digestion is carried out in tubes with sulphuric acid-salicylic acid-hydrogen peroxide and selenium. Total N was then measured by distillation then titration with standard 0.01NHcl, phosphorus was determined calorimetrically on spectrophotometer, potassium was determined by flame photometer and calcium, magnesium, copper, zinc, manganese and iron were determined using AAS. Results and discussion Soil ph The range and mean of ph (H 2O) values of the soils of the study areas are shown in Figure 1. The ph ranged from 5.83 to 7.96, with an overall mean of 6.96 (sd.±0.53). Except on eight farms, where the soil ph was slightly alkaline (>7.0), the soil ph of the soils from the other farms was generally neutral, indicating that, on all the sampled farms, the ph was satisfactory for the growth of crops and fodder. Figure 1: Range and mean of ph values of the soil samples collected in the peri-urban areas of Wote town in Makueni County and Wamunyu market in Machakos County 2

3 Soil nutrients and organic matter content Results of soil analysis indicated that with the exception of nitrogen (N), phosphorus (P), organic carbon (Org. C) and zinc (Zn), the other elements analyzed for, i.e. potassium (K), calcium (Ca), magnesium (Mg), copper (Cu), and iron (Fe), were above critical levels. The lowest, highest, mean and critical levels of total N, P, Org. C and Zn for all the farms sampled are presented in Figures 2, 3, 4 and 5, respectively. Total N ranged from 0.07 % to 0.16%, with a mean of 0.09% (Sd.±0.02) and was below the critical level (0.2%) on all the farms. Organic carbon ranged from 0.51% to 1.29%, with a mean of 0.91 (Sd. ±0.19) and was below the critical level (2.0%) on all the farms. Phosphorus ranged from 1.0 mg/kg to mg/kg, with a mean of mg/kg (Sd.±26.70) and was above the critical level (20 mg/kg) on 15 farms. Zinc ranged from 0.91 mg/kg to 9.54 mg/kg, with a mean of 3.47 (sd.±2.59) and was above the critical level (5 mg/kg) on 10 farms. Low organic matter content and N and P deficiencies have been reported in other areas in this region (Nadar and Faught, 1984; Ikombo, 1984; Okalebo et al., 1992; Okalebo et al., 1996; Okwach et al., 1999; Gachimbi et al., 2005; De Jager et al., 2005). Nutrient monitoring studies in this region have shown that the outflow of nutrients in most farms far exceeds input flows (Smaling et al., 1993; Gachene et al., 2000; Gachimbi et al., 2005; De Jager et al., 2005). This scenario has been attributed to continuous cultivation without adequate replenishment of nutrients, removal of crop residues for livestock feed and loss of nutrients through erosion, leaching and runoff. There have been no reports of widespread zinc deficiencies in the semi-arid areas in the past. However, the results of this study indicate that with time, zinc is likely to become limiting. Figure 2: Range and mean of total N from sampled farms in the peri-urban areas of Wote town in Makueni County and Wamunyu market in Machakos County 3

4 Figure 3: Range and mean of organic C. from sampled farms in the peri-urban areas of Wote town in Makueni County and Wamunyu market in Machakos County Figure 4: Range and mean of P from sampled farms in the peri-urban areas of Wote town in Makueni County and Wamunyu market in Machakos County 4

5 Figure 5: Range and mean of total Zn from sampled farms in the peri-urban areas of Wote town in Makueni County and Wamunyu market in Machakos County Levels of N, P and Zn in the manure applied on the farms Results of manure analysis indicated that with the exception of N, P and Zn, the other elements analyzed for, i.e. K, Ca, Mg, Cu, Mn and Fe, were above critical levels. The lowest, highest, mean and critical levels of N, P, and Zn for all the farms sampled are shown in Figures 6, 7 and 8, respectively. The N contents ranged from 0.1 to 2.1%, with a mean of 0.91% (sd.±0.47) and were below the critical level (3.0%) on all the farms. P levels ranged from 0.16 to 0.51%, with a mean of 0.28% (sd.±0.89) and were below the critical level (0.2%) on only two farms. Zn levels ranged from 11.2 to 118 mg/kg, with a mean of mg/kg (sd.±25.2) and were below the critical level in 10 farms. Low levels of N in manure produced on smallholder farms in this region have been reported by a number of investigators (Probert et al., 1992; Watiki et al., 1999; J. R. Okalebo, unpublished data). Low levels of N in manure produced in smallholder farms have been reported from other places in Africa. For instance, Mugirwa and Shumba (1986) reported N levels of 0.98% and 1.05% from Chiota and Svose communal areas, respectively, in Zimbabwe. Mokwunye (1980), working in West Africa, reported N levels ranging from 0.48 to 1.95%. The low levels of N have been attributed to mixing of manure with soil when scooping manure from bomas, which in most cases do not have a concrete floor, denitrification, brought about by wet conditions in the bomas, leaching and volatilization when manure is heaped outside after it has been removed from the bomas and left uncovered (Probert et al., 1992). 5

6 Figure 6: Range and mean of total N from manure samples obtained in farms in the peri-urban areas of Wote town in Makueni County and Wamunyu market in Machakos County Figure 7: Range and mean of P from manure samples obtained in farms in the peri-urban areas of Wote town in Makueni County and Wamunyu market in Machakos County 6

7 Figure 8: Range and mean of N from manure samples obtained in farms in the peri-urban areas of Wote town in Makueni County and Wamunyu market in Machakos County Implication of the manure quality on soil fertility maintenance The assertion that farmyard manure is capable of maintaining soil fertility in resource-poor smallholder crop-livestock farming systems presupposes that adequate quantities of good quality manure are available on farm. However, as shown by the analysis, the manure produced on these farms is of poor quality. It is particularly deficient in N and to some extent P. Past research findings have also indicated that most of the farmyard manure in the semi-arid areas of Kenya contains only one third of the N and P expected from fresh animal manure (Probert et al., 1992; Lee, 1993). A much more important constraint in the utilization of farmyard manure is the insufficient quantities available on farm. For instance, a recent survey (Itabari et al., 2013) showed that the average amount of animal manure produced on the farms in the peri-urban areas of Machakos town was 5.1 tonnes (s.d ±2.8) per season while that produced in the peri-urban areas of Wote town was 5.6 tonnes (s.d ±4.4) per season. The recommended application rate for maize is 8t/ha of good quality manure (Ikombo, 1984). This clearly indicates that, given the poor quality of the manure, these amounts are not sufficient to apply to even one hectare of cropland. However, Probert et al. (1992), working in the same region reported estimated rates of application of between 38 to 168 t/ha, but this was on farms where farmers practised a policy of applying manure to different terraces each year. For instance, one farm had applied manure to one out of ten terraces and another had applied to half of a terrace out of three. Thus, manure is not adequate to apply to the whole cropped area and presumably, farmers were applying these high rates so as to provide adequate nutrients to their crops. From the foregoing, it is evident that while manure is essential for soil fertility maintenance, the available supplies are of poor quality and insufficient and hence cannot maintain soil fertility. Maintenance of soil fertility for sustainable crop and livestock production in these areas is, therefore, only possible by augmenting manure with inorganic fertilizer, with manure supplying organic matter, phosphorus and micronutrients and inorganic fertilizer supplying mainly nitrogen. Conclusions and recommendations N was particularly deficient in all the soils of the surveyed areas and levels of Zn were below the critical level in most of the farms. Organic matter contents were also very low in all the farms surveyed. There is, therefore, a need to improve the levels of these soil nutrients and organic matter content. One way of addressing this problem, especially low organic matter content, is through application of adequate quantities of good quality manure. The N content of the manure, which is the principal source of 7

8 nutrients in the region was very low, hence there is a need to sensitize/train farmers on strategies for mitigating N losses from manure so as to improve its content. However, due to the low levels of N in the farmyard manure and the insufficient quantities available on farm, application of manure alone cannot maintain soil fertility for sustainable crop and livestock production. There is, therefore, a need to augment the available quantities of farmyard manure with inorganic nitrogen fertilizers. There is also a need to intensify production of legumes so as to increase N pool in the soil through N 2-fixation. Acknowledgement The authors are grateful to the Association for Strengthening Agricultural Research in Eastern and Central Africa (ASARECA) for funding this study and the Director, KARI for permission to publish the results. We are also grateful to all those who contributed to the success of this study. References De Jager, A., van Keulen, H., Mainah, F., Gachimbi, L.N., Itabari, J.K., Thuranira, E.G. and Karuku, A.M. (2005). Attaining sustainable farm management systems in semi-arid areas in Kenya: Few technical options, many policy challenges. International Journal of Agricultural sustainability.3, Gachene, C.K.K., Mureithi, J.G., Anyika, F. and Makau, M. (2000). Incorporation of green manure cover crops in maize-based cropping systems in semi-arid and sub-humid environments of Kenya. In: Mureithi, J., Gachene, C.K.K., Muyekho, F.N., Onyango, M., Mose, L. and Magenya, O. (eds.). Participatory technology development for soil management by smallholders in Kenya. Proceedings of the Second Scientific Conference of the Soil Management and Legume Research Network Projects, Mombasa, Kenya, June Gachimbi, L.N., Keulen van H., Thuranira, E.G., Karuku, A.M., Jager, de A., Nguluu, S., Ikombo, B.M., Kinama, J.M., Itabari, J.K. and Nandwa, S.M. (2005). Nutrient balances at farm level in Machakos (Kenya), using a participatory nutrient monitoring (NUTMON) approach. Land Use Policy 22: Hinga, G., Muchena, F.N. and Njihia, C.M.(1980). Physical and chemical mrthods of soil analysis. Ministry of Agriculture, National Agricultural Laboratories, Nairobi, Kenya. Ikombo, B. M. (1984). Effects of farmyard manure and fertilizers on maize in semi-arid areas of Eastern Kenya. E. Afr. Agric. For. J. 44: Itabari, J.K., Njarui, D.M.G., Gatheru, M. and Mutuoki, T. K. (2013). Nutrient management practices for vegetable production in smallholder crop-livestock farming systems in the peri-urban areas of semiarid eastern Kenya. In the Book of Abstracts of the Joint 27 th Soil Science Society of East Africa (SSSEA) and 6 th Africa Soil Science Society (ASSS), held in Nakuru, Kenya, 21 st - 25 th October, Jaetzold, R. and Schmidt, H. (1983). Farm management Handbook of Kenya. Vol. II/C: Natural conditions and farm management information. Ministry of Agriculture/GAT, Nairobi, Kenya. Jaetzold, R. Scmidt, H., Hornetz, B. and Shisanya, C. (2006). Farm Management Handbook of Kenya. Vol. 2. Natural Conditions and Farm Management Information, 2 nd Edition, Part C, Eastern Kenya, Subpart C1, Eastern Province. Lee, B. (1993). Escaping from hunger: research to help farmers in semi-arid Kenya to grow enough food. ACIAR Monograph No. 23. pp. 52. McCown, R. L. and Jonnes, R. K. (1992). Agriculture of semi-arid Kenya: problems and possibilities. In: Probert, M. E. (ed.). A search for strategies for sustainable dryland cropping in semi-arid Eastern Kenya. Proceedings of a Symposium held in Nairobi, Kenya, December ACIAR Proceedings No. 41. Canberra, Australia. pp Mokwunye, U. (1980). Interaction between farmyard manure and NPK fertilizers in savanna soils.in: Organic recycling in Africa. Rome,FAO,Soils Bulletin No. 43: Mugwira, L. M. and Shumba, E. M. (1986). Rate of manure applied in some communal areas and the 8

9 effect on plant growth and maize grain yields. Zimbabwe Agricultural Journal. 83: Nadar, H. M. and Faught, W. A. (1984). Maize yield response to different levels of nitrogen and phosphorus fertilizer application: A seven-season study. E. Afr. agric. For. J. Special Issue 44: Okalebo, J. R., Simpson, J. R. and Probert, M. E. (1992). Phosphorus status in cropland soils in the semiarid areas of Machakos and Kitui Districts, Kenya. In: Probert, M. E. (ed.). A search for strategies for sustainable dry land cropping in semi-arid Eastern Kenya. Proceedings of a symposium held in Nairobi, Kenya, December ACIAR Proceedings No.41. Canberra, Australia. Okalebo, J.R., Simpson, J.R., Probert, M.E., Okwach, G.E. and McCown,R.L. (1996). Maintenance of soil fertility under intensive maize cropping in Machakos District, Kenya. Proc.15 th Annual General Meeting Soil Science Society of East Africa (SSSEAA), Okwach, G.E. and Simiyu, C.S. (1999). Effects of land management on runoff,erosion and crop management in a semi-arid area of Kenya. E. Afr. Agric. For. J. 65, Probert, M. E., Okalebo, J. R., Simpson, J. R. and Jones, R. K. (1992). The role of boma manure for improving soil fertility. In: Probert, M. E. (ed.). A search for strategies for sustainable dry land cropping in semi-arid eastern Kenya. Proceedings of a symposium held in Nairobi, Kenya, December ACIAR Proceedings No. 41. Canberra, Australia. Smaling, E.M.A., Stoorvogel, J.I. and Windmeijer, P.N. (1993). Calculating soil nutrient balances in Africa at different scales. II. Different Scale. Fert. Res. 35, Watiki, J.M., Gichangi, E.M., Itabari, J.K., Karuku, A.M. and Ngulu, S.N. (1999). The effects of rate and placement of boma manure on maize yield in semi-arid eastern Kenya. In: Proceedings of the 6 th Biennial KARI Scientific Conference, Nairobi, Kenya, 9-13 November