Browsing by Author "Nair, P.K."
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Item Alley cropping of maize with calliandra and leucaena in the subhumid highlands of Kenya Part 1. Soil-fertility changes and maize yield(Kluwer Academic Publishers, 1999-06) Mugwe, Jayne; Mugendi, Daniel N.; Nair, P.K.; O’neill, M.K.; Woomer, P.L.Although N-rich leaf biomass of multipurpose trees is known to be a good source of N to crops, integrating such trees into crop production systems is a major challenge in the development of viable agroforestry systems. An approach to integrating calliandra (Calliandra calothyrsus Meissner) and leucaena (Leucaena leucocephala (Lam.) de Wit), two promising agroforestry tree species, into maize (Zea mays L.) production system was investigated in the subhumid highlands of central Kenya during four maize-growing seasons from 1994 to 1996. The experiment consisted of maize plots to which tree prunings obtained from hedgerows grown either in situ (alley cropping) or ex situ (biomass transfer from outside) were applied. When alley-cropped with leucaena, maize produced significantly higher yields compared to maize monoculture (both non-fertilized and fertilized) treatments, but when alley-cropped with calliandra, the yield of maize was less than that of the monocropped unfertilized control. Application of ex situ grown calliandra and leucaena prunings with or without fertilizer resulted in higher maize grain yield than in the nonfertilized and fertilized treatments. Yields of calliandra alleycropped maize were 11% to 51% lower than those of nonalley-cropped treatments receiving calliandra prunings from ex situ grown trees; the decrease was 2% to 17% with leucaena, indicating that calliandra hedges were more competitive than leucaena hedges. The alley-cropped prunings-removed treatments produced the lowest maize yields. The study showed that, in the subhumid tropical highlands of Kenya, inclusion of calliandra hedges on cropland adversely affected maize yields. On the other hand, alley cropping with leucaena was advantageousItem Alley cropping of maize with calliandra and leucaena in the subhumid highlands of Kenya Part 2. Biomass decomposition, N mineralization, and N uptake by maize(Kluwer Academic Publishers, 1999-06) Mugendi, Daniel N.; Nair, P.K.; Mugwe, Jayne; O'Neill, M.K.; Swift, M.J.; Woomer, P.A major challenge in developing agroforestry approaches that utilize tree-leaf biomass for provision of N to crops is to ensure synchrony between the N released from decomposing prunings and N demand by crops. A study was conducted in the subhumid highlands of Kenya to assess the rate of decomposition and mineralization of soil-incorporated Calliandra calothyrsus Meissner (calliandra) and Leucaena leucocephala (Lam.) de Wit (leucaena) tree biomass and maize roots (Zea mays L.) both in an alley cropping and a sole cropping system. The amount of mineralized N peaked four weeks after planting (WAP) maize in all the treatments during both seasons of 1995. Cumulative mineralized N at week 20 ranged from 114 to 364 kg N ha−1 season−1, the absolute control treatment giving the lowest and the prunings-incorporated treatments giving the highest amounts in the two seasons. Total N uptake by maize, ranging from 42 to 157 kg ha−1 season−1, was lowest in the 'alley-cropped, prunings-removed' treatments, and highest in the 'non alley-cropped-prunings-incorporated' treatments. The apparent N recovery rate by maize was highest in the fertilizer applied treatments in the two seasons. Decomposition rate constants (kD) ranged from 0.07 to 0.21 week−1, and the rates among the different plant residues were as follows: leucaena < calliandra < maize roots. Nitrogen release rate constants (kN), ranging from 0.04 to 0.25 week−1, followed a similar pattern as the rate of decomposition with leucaena releasing the highest amount of N followed by calliandra and lastly by maize rootsItem Nitrogen recovery by alley-cropped maize and trees from 15N-labeled tree biomass in the subhumid highlands of Kenya(Springer-Verlag, 2000-05) Mugendi, Daniel N.; Nair, P.K.; Graetz, D.A.; Mugwee, Jayne; O'Neill, M.K.The effectiveness of tree-leaf biomass as a source of N to crops in agroforestry systems depends on the rate at which crops can obtain N from the biomass. A study was conducted to determine the fate of 15N labeled, soil-applied biomass of two hedgerow species, Calliandra calothyrsus Meissner (calliandra) and Leucaena leucocephala (Lam.) de Wit (leucaena), in the subhumid highlands of Kenya. Labeled biomass obtained from 15N fertilized trees was applied to microplots in an alley cropping field and maize planted. N uptake and recovery by maize and hedgerow trees was periodically determined over a 20-week period during the short rain (1995) and the long rain (1996) growing seasons. In maize crop from treatments that received leucaena biomass, higher N uptake and recovery were recorded than in maize from the plots that received calliandra biomass. However, N uptake and recovery were higher in calliandra tree hedges than in leucaena hedges, indicating differences in N uptake by the two tree species. The largest fraction (55–69%) of N in the applied tree biomass was left in the soil N pool, 8–13% recovered by maize, 2–3% by tree hedges, and 20–30% could not be accounted for. Some of the unaccounted for N may have been left in the wood and root portions of the tree hedges and in the bulk soil below the 20-cm depth. The study shows that only a small fraction of the N contained in the N-rich biomass that is applied to the soil is taken up by the current season's crop, suggesting that a major benefit may be in the build-up of the soil N store.Item Predicting decomposition patterns of tree biomass in tropical highland microregions of Kenya(Kluwer Academic Publishers, 1997) Mugendi, Daniel N.; Nair, P.K.Decomposition- and nitrogen-release patterns of biomass from three agroforestry multipurpose trees (Calliandra calothyrsus, Cordia africana and Grevillea robusta) were investigated in four contrasting environments (microregions) in the Kenyan tropical highlands during two cropping seasons. Dried leafy biomass was placed in 2-mm litter bags, buried at 15-cm depth and recovered after 2, 4, 7, 10, 15 and 20 weeks. Decomposition patterns were best described by first-order exponential decline curves. The decomposition rate constants ranged from 2.1 to 8.2 yr−1, and the rates of decomposition among the species were in the order: calliandra ≥ cordia > grevillea. There was a species-by-environment interaction during both seasons, but the nitrogen released did not follow such a pattern. Among the three tree species, calliandra released the highest amount of cumulative N, followed by cordia and grevillea. Using multiple regression techniques, decomposition pattern was described as a function of three groups of factors: biomass quality (N, C, lignin and polyphenol), climate (soil temperature and rainfall), and soil conditions (pH, soil organic C, total N and P). For all the species and factors combined, the adjusted R 2 values were 0.88 and 0.91 for seasons 1 and 2, respectively. Among the three groups of factors, climate and biomass quality had the most influence on decomposition rates. Climatic factors accounted for 75% of the total rate of decomposition in season 1 (‘irregular’ season with less rainfall and more soil temperature fluctuations), whereas biomass quality factors were more influential in season 2 (‘regular’ season), accounting for 65% of the total variability.Item World Economic Plants: A Standard Reference(Kluwer Academic Publishers, 2001) Nair, P.K.; Mugendi, Daniel N.Use of scientific (Latin) names of living organisms is a basic norm in all scientific literature. Yet, to write these names correctly is a daunting task for not only the novices, but even seasoned professionals. This is particularly true in agroforestry literature, where we often deal with little-known and underexploited species. Many authors have a tendency to refer to them with common or parochial names only. But different plants may have the same common name and the same plant may have different common names in different places. Furthermore, as knowledge evolves continuously, the Latin names of some of the plants, especially the little-studied ones that are common in agroforestry, may be revised according to the rules of the International Code of Botanical Nomenclature. Therefore, it is essential that unambiguous and currently accepted Latin names of plants are given in scientific literature and even in international commerce. Authoritative books and well-researched reference materials that accurately give this information, though a must for scientific writing, are hard to find. This remarkable book fills that void. It is a thoroughly researched and comprehensive publication, which contains taxonomic information for nearly 10,000 species of economically important vascular plants from all over the world. That the book was reviewed before its publication by 150 specialists is a feature that most other publications cannot claim. The book contains two major parts, each arranged alphabetically. The first, 536 pages long, is the ‘Catalog of Economic Plants.’ It contains scientific names of vascular plants along with associated data such as synonymy, common names, economic impacts, and geographical distributions. The second part, the ‘Index to Common Names,’ is 213 pages of information in small print, providing a list of 19,200 common names, including nearly 7,500 non-English derivations, of the plants included in Part one. Thus, starting from a common name of a plant, a user can locate its relevant botanical data in Part one. As already mentioned, a reference book of this nature is a must for all agroforestry students and researchers. Almost all the trees that this reviewer has looked for randomly are listed in the book. If some are not (e.g., Allophyllus africanus P. Beauv., Conocarpus lancifolius Engl., and Rothmania spp.), it could well be that the species have undergone name changes, about which the reviewer is not aware. Admittedly, the common names are not exhaustive, especially when it comes to non- English derivations; but it is almost impossible, nor is it necessary, to list all the innumerable local names of all the species in a compilation like this. Readers need to be cautioned, however, that this book is not a species-identification guide. The hard-bound book is very well produced. Its consistency of formatting is admirable. All in all, it is an invaluable reference book. By producing this book, its authors and the Agricultural Research Service of the United States Department of Agriculture that supported the compilation of the book have provided an outstanding service to plant-research community all over the world.