Traditional soil P test methods estimate plant available inorganic P but ignore the less available inorganic and organic P pools. In low-input systems where fertilizer P additions are very low to nil, these less available P pools may be a better measure of potential plant available P, particularly in highly weathered soils. The objectives of this study were to determine the size and changes in soil P pools in the nonfertilized and fertilized treatments of a long-term continuous cultivation experiment established on a Typic Paleudult in Yurimaguas, Peru. A modified version of the Hedley et al. procedure was used to sequentially fractionate soil P into increasingly recalcitrant organic and inorganic pools. The use of path analysis highlights the interactions among P pools and the different roles of the pools in P cycling between the nonfertilized and fertilized system. For the fertilized system, the NaOH-extractable inorganic P pool acts as a sink for fertilizer P but desorption is rapid enough to maintain high levels of plant available p For this system, inorganic P pools explain 96 percent of the variation in the level of available pOrganic P is primary source of plant-available P in the nonfertilized system and explains 44 percent of the variation in the level of available P, measured by anion exchange resin, is dependent on crop residue (b values _ standard error = 4.98 _ 3.57), whereas yield depends most strongly on the available P(0.16 _ 0.11) and on NaOH-extractable organic P(-0.17 _ 0.11). The lack of stability in organic P levels in the first 10 yr illustrates the need for long-term experiments. The presented results support the notion that traditional soil P tests are inadequate for low- to no-input systems.
Tag: humid tropics
Managing for biodiversity in humid tropical forests
One of the major issues surrounding the debate on sustainability of management of tropical forests is the impact of different forest management strategies on biodiversity. Recent research has suggested a number of options for minimising the risks to biodiversity of forestry operations. The maintenance of extensive conventional national parks and equivalent reserves still constitutes the best option from the purely biological standpoint. However, social, economic and demographic realities coupled with increased knowledge of the ecology and distribution of tropical forest species, suggests that appropriate forestry practice can contribute significantly to biodiversity conservation. The optimal strategy should be based upon a system of conventional protected areas, complemented by a reduction of the impact of harvesting and the retention of unlogged refugia in logged-over-forests.
Tropical moist forests and protected areas: the digital files
Dynamics of soil physical properties in Amazonian agroecosystems inoculated with earthworms
The combined use of earthworm inoculation and organic inputs is considered an efficient way to improve traditional slash-and-burn agriculture in the humid tropics. This study tests the hypothesis that the resistant macroaggregate structure that results from earthworm activities is likely to promote sustainability by favoring water infiltration and soil aeration. Six successive crops (maize [Zea mays L.]-rice [Oryza sativa L.]-cowpea [Vigna unguiculata (L.) Walp.]-rice-rice-rice) were grown from March 1990 to January 1993 on a fine-sandy, siliceous, isohyperthermic Typic Paleudult previously covered by forest at Yurimaguas (Peruvian Amazonia). The experimental design included a combination of three organic residue treatments (without residues, with crop residues, and with crop residues plus green manure), with or without earthworm (Pontoscolex corethrurus) inoculation (36 g fresh weight m2). Soil physical properties (bulk density, total porosity, infiltration, sorptivity, soil water tension, and aggregate-size distribution) were measured before clearing and after harvesting each crop. The proportion of macroaggregates (>1 cm) increased from 25.1 to 32.7% in inoculated treatments, whereas the proportion of small aggregates (<2 cm) decreased from 33.2 to 26.1%, and no change was observed in the intermediate (2-10 mm) category. In the control treatment, no significant changes were observed. Earthworm activities significantly increased bulk density (from 1.12 to 1.23 Mg m3), and decreased porosity (from 58 to 53%) and sorptivity (from 0.45 to 0.15 cm s1/2). Soil water tension was also affected by the presence of earthworms through increased water uptake by larger plants and changes in soil structure. Longer term experiments are necessary to confirm that the activity of the earthworm may not eventually have detrimental effects.
Fertilizer nitrogen movement in central Amazon oxisol and entisol cropped to corn
Nitrogen fertilization experiments were conducted on a Oxisol and Entisol in the Central Amazon to evaluate the influence of soil properties and rainfall distribution on soil inorganic N movement and N recovery by corn (Zea mays L.). One corn crop was grown during the wet season on each site. A second crop was planted in the Oxisol during the dry season. Inorganic N was monitored in urea-N treatments (0 to 160 kg ha1) to a depth of 0.60 m by periodic soil sampling during each crop. During the wet season large N losses by leaching occurred in both soils with 120 or 160 kg ha1 of applied N. Differences in soil permeability and corn rooting depth between soils contributed to a greater movement of N into subsoil layers in the Oxisol than the Entisol. However, N leaching beyond 0.60 m in the Oxisol was delayed, apparently because of NO3 adsorption in the net positively charged subsoil layers. Corn yields and N recovery in the Entisol were higher than in the Oxisol, during the wet season. During the dry season N leaching in the Oxisol was greatly reduced, relative to the previous wet season, by split applications of fertilizer N and lower cumulative rainfall (300 vs. 1012 mm). Management practices which promote root growth into acid subsoil layers of the Oxisol would increase plant access to soil N, improve crop N recovery and reduce fertilizer N requirements.
Sustainable alternatives to slash and burn agriculture and the reclamation of degraded lands in the humid tropics
This paper describes the rationale and proposed activities of the Slash and Burn Programme which can be considered a direct response to agenda 21’s recommendations and thus an interval part of the Global Forest Policy. It draws heavily from the programme working documents and project briefs developed by a steering group. Slash and burn agriculture (shifting cultivation) accounts for about 50 to 75% of the 14 million hectares of moist tropical forests currently converted every year. Tropical deforestation is responsible for 25% of current global warming, for most of the decimation of plant and animal genetic diversity, and threatens the stability of many watersheds. Rates of deforestation have doubled over the last two decades they are likey to continue increasing and to contribute a relatively larger proportion of global warming. Shifting cultivation is aconsequence of complex socioeconomic factors that drive poor farmers and migrants into the forest margins.
Alternatives to Slash-and-Burn agriculture, symposium ID-6: 15th International Soil Science Congress, Acapulco, Mexico 1994
Long term impact of Acacia auriculiformis woodlots growing in rotation with cassava and maize on the carbon and nutrient contents of savannah sandy soils in the humid tropics (Democratic Republic of Congo)
Agroforestry – a policy imperative for Vietnam
Agroforestry has been traditionally practiced, although it does not go under the name ‘agroforestry’. The VAC-R-systems (vuon-ao-chuong-rung or garden-pond-livestock-forest) expanded largely in the 1960-90s. Taungya is often practiced to introduce reforestation by intercropping annu-al crops with tree seedlings during the first 1-3 years until the tree canopy has closed.‘Integrated agroforestry’ is originally used to denote the integration of trees and crops (in one field), such as intercropping, alley cropping, parkland – sometimes includ-ing livestock. Agroforestry in the northern uplands of Viet Nam can at best be described as temporarily integrated in transition from segregated mosaic monocultures of maize or cassava to timber-tree mono-plantation (typically Aca-cia, Eucalypts, Manglietia, Melia).
Agroforestry and the development of tropical forestry
This paper is divided into three parts. Part one deals specifically with deforestation. Deforestation is caused mainly by 1) conversion of forest lands into agricultural lands, 2) the quest for fuelwood and building poles, and 3) social and economic deprivation. The author warns of the dangers of confusing symptoms with cause of deforestation. Before embarking on the subject of agroforestry, the author, in the second part of this paper, gives a broad view of the ecological requirements of various plant species. The final, well detailed and comprehensive section deals specifically with agroforestry related aspects. A list of suitable agroforestry trees, shrubs and fodder crops is included.