Microarthropods, such as soil mites (Acari) and springtails (Collembola), with body width between 0.08 mm and 0.5 mm play important roles in soil fertility maintenance through their regulatory activities in decomposition and nutrient turnover. Observations were made at IITA, Ibadan, southwestern Nigeria to evaluate the effects of natural regrowth of vegetation — mainly the shrub Chromolaena odorata — and three planted woody fallow species (Acacia leptocarpa, Senna siamea, and Leucaena leucocephala) on soil microarthropods in a degraded Alfisol. Populations of soil microarthropods were higher in the rainy season than the dry season, and populations were greater under natural fallow than for continuous cropping with maize (Zea mays) and cassava (Manihot esculenta). Populations of soil microarthropods were comparable under leucaena and natural fallow, but populations in the rainy season were 38% higher under senna than natural fallow and 36% higher under acacia than natural fallow. Regression analysis indicated that soil microarthropod population under fallow species was positively correlated with the lignin contents of leaf litter.This revised version was published online in November 2005 with corrections to the Cover Date. 相似文献
Four shrub/tree species, Alchornea cordifolia, Pennisetum purpureum, Chromolaena odorata, and Calliandra calothyrsus were
evaluated for their potential contribution to soil fertility restoration after two years fallow. Standing biomass, root distribution,
nutrient content in the biomass, decomposition and nutrient release patterns, and association with mycorrhizae were the evaluation
parameters. Alchornea and Pennisetum produced thehighest above-ground biomass, 66 t and 54 t/ha respectively. Pennisetum had
more than 19 t/ha of root, 92% of which was in the 20 cm top soil. Alchornea had 74% of it roots in this soil layer, mostly
as coarse roots while Calliandra had a deeper root system. Alchornea fallow accumulated more N and Ca, and Pennisetum fallow,
more K than others, and mycorrhizae were mostly associated with Alchornea roots. The ranking of the different species for
the decomposition rate was: Chromolaena > Pennisetum > Calliandra = Alchornea. Also release of nutrients during decomposition
followed the order K > N > Ca. Alchornea and Pennisetum could be recommended as green manure species especially when high
quantities of material are needed for weed or erosion control. Calliandra and Chromolaena, because of the flush of nutrient
during early mass, loss can be used as mulch when the crop demand of nutrient is high. Alchornea decomposed slowly and therefore
could be used to improve Chromolaena mulch, thus contributing to the build up of soil organic N and providing both short-
and long-term nutrient release.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
The impacts of thinning, fertilization and crown position on seasonal growth of current-year shoots and foliage were studied in a 13-year-old loblolly pine (Pinus taeda L.) plantation in the sixth post-treatment year (1994). Length of new flushes, and their needle length, leaf area, and oven-dry weight were measured in the upper and lower crown from March through November. Total shoot length was the cumulative length of all flushes on a given shoot and total leaf area per shoot was the sum of leaf areas of the flushes.
By the end of June, first-flush foliage reached 70% of the November needle length (14.3 cm) and 65% of the final leaf area (15.0 cm2). Cumulative shoot length of first- and second-flush shoots achieved 95% of the annual length (30.3 cm), whereas total leaf area per shoot was 55% of the final value (75.3 dm2). Fertilization consistently stimulated fascicle needle length, dry weight, and leaf area in the upper crown. Mean leaf area of upper-crown shoots was increased by 64% six years after fertilization. A significant thinning effect was found to decrease mean leaf area per shoot in the crown. For most of the growing season, the thinned-fertilized trees produced substantially more leaf area per shoot throughout the crown than the thinned-nonfertilized trees. These thinned-fertilized trees also had greater needle length and dry weight, longer first flush shoots, and more leaf area per flush than trees in the thinned-nonfertilized plots. Needle length and leaf area of first flush shoots between April and July were linearly related to previous-month canopy air temperature (Ta). Total shoot length strongly depended on vertical light gradient (PPFD) within the canopy, whereas shoot leaf area was a function of both PPFD and Ta. Thus, trees produced larger and heavier fascicles, more and longer flush shoots, and more leaf area per shoot in the upper crown than the lower crown. We conclude that thinning, fertilization, and crown position regulate annual leaf area production of current-year shoots largely by affecting the expansion of first flush shoots and their foliage during the first half of the growing season. 相似文献