Department of Crop Science
Permanent URI for this collectionhttp://localhost:4000/handle/20.500.12092/1825
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Item Do Mixed-Species Legume Fallows Provide Long-Term Maize Yield Benefit Compared with Monoculture Legume Fallows?(Wiley, 2009-11-01) Ndufa, James K.; Gathumbi, Stanley M.; Kamiri, Hellen W.; Giller, Ken E.; Cadisch, GeorgThe deliberate planting of fast-growing N2–fixing legume monoculture species in rotation with cereal crops can be an important source of N for soil fertility replenishment. We hypothesized that mixed-species fallows have a higher potential of giving long-term residual benefits in terms of biomass, nutrients, and quality of residuals leading to long-term nutrient supply to postfallow maize (Zea mays L.) crops. To test these hypotheses, two experiments were established in farmers' fields on very fine Kandiudalfic Eutrudox soils with monoculture and mixed-species fallows. Treatments included: sesbania [Sesbania sesban (L.) Merr.], crotalaria (Crotalaria grahamiana Wight and Arn.), pigeonpea [Cajanus cajan (L.) Millsp.], siratro [Macroptilium atropurpureum (DC.) Urb.], and calliandra (Calliandra calothyrsus Meissn.) as monoculture-species fallow and mixture fallows of sesbania + crotalaria, sesbania + pigeonpea, sesbania + siratro, or sesbania + calliandra compared with continuous maize cropping with or without N fertilizer, and natural weed fallow. Total aboveground biomass ranged from 4.1 to 20.5 Mg ha−1 for monoculture and 7.8 to 23.3 Mg ha−1 for mixed-species fallows. Recyclable fallow biomass N ranged from 70 to 313 kg ha−1 and there was a positive interaction in some mixtures leading to increased N accumulation. Postfallow maize yields for fallows over five cropping seasons were 161–272% or 61–103% higher when compared with continuous maize without or with N fertilizer, respectively. Long-term postfallow effects on maize yield were linearly related to the amount of recycled fallow N yield. Thus, choice of fallow species to mix should be primarily driven by a better risk management strategy and an increased basket of multiple products and services.Item Effects of blended fertilizers on soil chemical properties of mature tea fields in Kenya(2018-06) Sitienei, Kibet; Kamiri, Hellen W.; Nduru, Gilbert M.; Kamau, David M.Kenya’s tea industry depends predominantly on imported NPK fertilizers to replenish nutrients removed through plucking. In this respect, two blended fertilizers containing NPKS 25:5:5:4+9Ca+2.6Mg and NPKS 23:5:5:4+10Ca+3Mg with trace elements have been produced in the country. However, contribution of the blended fertilizers to optimal tea yields had not been determined. The study aimed to evaluate the optimal levels of the two blended fertilizers on tea grown in the highlands of Kenya. The blended fertilizers were evaluated in two sites, i.e. Timbilil estate in Kericho and Kagochi farm in Nyeri. The trial was laid out in a randomized complete block design with two blended fertilizers and the standard NPK 26:5:5 as a control. The treatments were applied at four fertilizer rates (0-control, 75, 150 and 225 kg N ha-1 yr-1), with three replications. The results showed that application of 225 kg N ha-1 yr-1 blended fertilizer NPKS 25:5:5:4+9Ca+2.6Mg in Timbilil produced mean yield of 2,995 kg Mt ha-1 compared with 3,099 kg Mt ha-1 from the standard NPK. In Kagochi, the highest yield was 1,975 kg Mt ha-1 obtained from the application of the same blended fertilizer NPKS 25:5:5:4+9Ca+2.6Mg at 75 kg N ha-1 yr-1. The highest yields in both sites were obtained during a warm-dry season except in 2015–2016. This study concluded that based on the annual and seasonal yields, the two blended fertilizers and the standard type had the same effectiveness, irrespective of clones and sites. However, the fertilizer rates affected the tea yield.Item Nutrient Budget and Economic Assessment of Blended Fertilizer Use in Kenya Tea Industry(Hidawi, 2018-11-18) Sitienei, Kibet; Kamiri, Hellen W.; Nduru, Gilbert M.; Kamau, David M.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.