Impacts of human activity on tropical soil quality in relation to future land productivity and biodiversity Lauren Bolte Department of Religion, University of Puget Sound ABSTRACT The high rates of tropical forest clearing followed by inten sive agriculture may significantly degrade the soil s original nutrient content and chemical composition, reducing future productivity and future restoration efforts. Land use impacts were determined by collecting soil samples from four sites in San Luis, Costa Rica. Three areas presented different agricultural uses, and the fourth was an area of forest, comparatively untouched by human activity. To evaluate existing nutrient levels, six tests were conducted from three soil samples from each site: ph, N, P, K, Al and Fe. Trends were found in that the site with the heaviest land use experienced the most change in nutrient levels compared to the forest soil. The three different agricultural areas displayed differing results, even as they were all within th e same farming community, no more than 15m from one another. RESUMEN Las altas tasas de deforestaciÃ³n en los bosques tropicales debido a la agricultura pueden degradar significativa el contenido original de nutrientes y composiciÃ³n quÃmica de los suelos , reduciendo la productividad futura y los esfuerzos de restauraciÃ³n . El impacto del uso del suelo se de terminÃ³ colectando muestras de suelo en cuatro sitios en San Lu i s, Costa Rica. Tres Ã¡reas presentan usos agrÃcolas de diferente impacto, y la cuarta es un Ã¡rea de bosque. Se encontraron tendencias a mayor cambio de nutrientes en los sitios con mayor explotaciÃ³n en comparaciÃ³n al suelo del bosque. Las tres Ã¡reas agrÃcolas mostraron diferentes resultados, inclusive estando en la misma comunidad agrÃcola . IN TRODUCTION Soil in the Tropics Despite the fact that Tropical forests are among the most productive ecosystems on the planet, tropical soils are extremely infertile Sanchez, 1992. They lack important nutrients and are highly weathered Terborgh, 2008. So called mineral soil in the Tropics is nearly devoid of soluble minerals of any kind for roots to absorb Richards, 1981. This poor soil state is a result of more than millennia of torrential rain exposure Terborgh, 1992. Rains that are mildly aci dic are at the core of the problem. These rains percolate down through the soil, washing all dissolved minerals away into streams. This leaching process does not leave behind much to benefit the plants. What remains is a barren substrate comprised of ma sses of mostly iron, aluminum oxides and other insoluble mineral, which are, not useful and are even toxic to most plants. Despite the great diversity of soil existing in the tropics almost two thirds of all tropical soils are relatively infertile oxisols and utisols, containing clays with scant soluble minerals Terborgh, 1992. These soils also are generally deficient in bases and
have high levels of acidity Richards, 1981. The acidity disrupts the ability of roots to absorb nutrients. These soils are deficient in key minerals such as potassium, phosphor ous, carbon, magnesium and sulf ur Stalland, 2006. The key factor concerning the tropic s nutrient poor soil, yet high productivity lies in the litter carpeting the forest s floor. The nutrients of tropical ecosystems are mainly found in the living and recently dead organic matter decomposing in the thin cap of topsoil Richards, 1981. For many tropical forests, the mineral soils deep beneath the topsoil mainly act as anchoring for trees and a wate r supply for roots Terborgh, 1992. Issues of Tropical Agriculture As a result of relatively low soil fertility and high weathering only around 20 percent of the soils of the humid tropical region are capable of sustaining agriculture with current tech nology, and the majority of the land in the area has been intensively developed Terborgh, 1992. At the same time, it is relatively rare to find sites on which the natural vegetation and soils have not been disturbed, to a great or lesser degree, by huma ns Anderson et al., 1993. Tropical deforestation rates, though difficult to calculate, are also unquestionably high, and the vast majority of the forest clearing in Latin America is for agricultural purposes Holl, 1999. In particular this land create s pastureland for cattle grazing Amelung & Diehl 1992, Fearnside 1993. Pasture development in Latin America is responsible for about 10 percent of tropical deforestation Smith et al., 1992. For example, Costa Rica, which was once almost completely co vered in forest, is now almost half 46% cattle pasture WRI, 1998. Agriculture plays a critical role in the economies of tropical countries and remains an essential part to a great population of local farmers and their families, upon which their live lihoods depend. The warm temperatures and high precipitation can produce a wide range of crops year round, and farmers take full advantage. However, these same conditions may degrade soil quality when coupled with deforestation and agriculture. Soil qual ity, though broadly understood, emphasizes the capacity of soil to perform services including the production of plants and animals and the transport and regulation of matter, water and other compounds present in or added to soils Wander et al., 2002. Add itionally, soil quality, or SQ, is described as reflecting appreciation for soils fitness for use Larson and Pierce, 1994 and the capacity of soil to resist and recover from degradation Blum, 1998; Greenland and Szabolcs, 1994. Compared to the natur al ecosystems from which they were formed, the composition, abundance, and activity levels of the soil community in agricultural systems are notably different Matson et al., 1997. Overall, it is generally understood that soils are depreciated by land tra nsformation, and their ability to recover from such degradation is reduced. Tropical land use leaves behind a mosaic of forest patches, cattle pastures, row crop agriculture and fallow lands that may support secondary forests. What tropical biodiversity remains will live in this matrix and will ultimately depend on what soil fertility remains. This will not only determine future human land use, but the fate of restoration/reforestation efforts. Studies of lowland wet forest areas clearly show a decline i n soil fertility that will compromise future land uses, including restoration Martinez Sanchez and Sanchez Beltran, 2003. In montane areas, particularly those near volcanoes, the soils are more fertile Andisols Clark et al., 2000. Here, I examine
soi l fertility for common land uses in Monteverde, Costa Rica. I compare major soil nutrients between common land uses and forest to see if Andisols suffer the same eventual fate as lowland Ultisols and Oxisols under agricultural use. METHODS Study Sites Four study sites were located in San Luis, Costa Rica within Finca la Bella. San Luis is a small farming community. The community is predominantly comprised of individual small, rural, family farms, or larger coop farm environments. It has not been affec ted by the presence of tourism as seen in Monteverde and Santa Elena. The area was first settled in 1915, and more and more settlers began moving into the area around 1930 Nadkarni et al., 2000. The elevation of the Finca la Bella area is at 1100 meter s, and the forest above and surrounding the farming communities is considered formally premontane moist forest. Four sites were sampled, three typical areas per site. The three different samples per site had to be at least 8 meters away from each other. The four sites were: 1 a coffee farm, 2 a cattle farm, 3 a organic vegetable farm, and 4 the forest on the upper slopes of Finca la Bella. The first three samples represented various types of human land use, while the forest represented a comparison for what the soils of the area were like without any human alteration. Basic Soil Features of Andisols Clark et al. 2000 characterize the soils of Monteverde as Andisols and further classify them as Udands because they formed under udic, or wet, condit ions. Andisols have poorly to moderately differentiated soil horizons. Andisols are soils that have formed in volcanic ash or other volcanic ejecta. They differ from those of other orders in that they typically are dominated by glass and poorly crystalli ne colloidal materials such as allophane, imogolite, and ferrihydrite. As a result, Andisols have andic properties unique chemical and physical properties that include high water holdin g capacity and the ability to 'fix' and make unavailable to plants large quantities of phosphorus . Globally, Andisols are the least extensive soil order and only account for ~1% of the ice free land area http://soils.ag.uidaho.edu/soilorders/andisols.htm. Because they are generally quite young, Andisols typically are very fertile except in cases where phosphorus is easily fixed this sometimes occurs in the tropics. They can usually support intensive cropping, with areas used for wet rice in Java supporting some of the denses t populations in the world. Other Andisol areas support crops of fruit , maize , tea , coffee or tobacco http://soils.usda.gov/technical/classification/orders/andisols.html. Andisols are divided into 8 suborders: Aquands , Gelands, Cryands , Torrands , Xerands , Vit rands , Ustands , and Udands . Monteverde s Ugand Andisols are highly weathered, with lots of clay and low available Phosphorus. Soil Sample Analysis For each sample taken, nutrient tests were conducted to determine nutrient levels at each site. Six individu al tests were performed upon each sample from each site. The samples
were tested for: 1 Ph, 2 Nitrogen nitrate, 3 Potassium, 4 Phosphorous, 5 Aluminum, and 6 Iron. All tests were conducted using the LaMotte STH Series Combination Soil Outfit te st kit, pH was determined by combining a small soil sample with demineralizer solution and soil flocculating reagent and then testing the resulting liquid. Nitrogen, Potassium, Phosphorous, Aluminum and Iron were all tested using a general soil extract res ulting from combining universal extract solution with a small sample of soil, shaking, and then filtering the soil. Here is a brief summary of the importance of each measure to soil fertility. pH: pH measurement is a simple means by which the production potential of a soil can be evaluated LaMotte, 1994. pH refers to the degree of effective acidity or alkalinity of a substance LaMotte, 1994. The Ph scale ranges from 0 14 with a pH value of 7.0 being neutral, meaning neither acid nor alkaline; pH val ues below 7.0 are acidic, and values above 7.0 are alkaline LaMotte, 1994. The tropics generally have more acidic soils Stalland, 2006. Soil pH primarily affects soil organism growth and activity, which means that pH, affects the amount of available nutrients gained from organic matter decomposition Stalland, 2006. There is a large variation in optimal pH levels for different crops LaMotte, 1994. Nitrogen: Nitrogen is required by nearly all biochemical processes that compose and sustain plant li fe Stalland, 2006. In that sense, nitrogen is an essential nutrient in the growth of plants. It aids in the absorption of essential nutrients Stalland, 2006. Nitrogen is an indispensable nutrient element, as when used at the recommended rates, imp roves the quality of leaf crops, and stimulates the utilization of potassium, phosphorous and other essential nutrient elements LaMotte, 1994. Plants take up nitrogen in the form of nitrate and ammonium and become part of the soil through fixation from atmospheric N 2 using bacteria associated with legumes Stalland, 2006. The above ground growth of plants is enhanced by nitrogen LaMotte, 1994. In the tropics specifically, nitrogen in the form of nitrate is absorbed by plants, but has the potential f or leaching out quickly Kohnke, 1995. Phosphorous: Phosphorous is critical in the strong growth of the plant and activity of its cells LaMotte, 1994. It promotes healthy root development Stalland, 2006. Phosphorous stimulates the formation of fat s, convertible starches, and healthy seed LaMotte, 1994. With the stimulation of rapid cell development in the plant, phosphorous can naturally increase disease resistance LaMotte, 1994. Life, whether it is plant or animal, cannot exist without phosp horous and the soil serves as the principal source LaMotte, 1994. Animals utilize plants for food and by doing so secure phosphorous indirectly, while plants secure their phosphorous directly from the soil LaMotte, 1994. In the tropics, phosphorous d eficiencies are common as a result of high leaching Kohnke 1995. This deficiency causes many tropical farmers to invest in commercial fertilizers Nadkarni, 2000 The availability of phosphorous in the tropics also possesses a
connection to the Ph of so il, in that it becomes available to plants only when soil acidity falls between 5.5 and 6.5 LaMotte, 1994. Potassium: Potassium plays a vital role in the physiological and biochemical functions of plants LaMotte, 1994. It improves the general healt h of the plant, aids in photosynthesis, and the uptake of other nutrients Stalland, 2006. By improving the health of the plant, it also develops stronger defense against disease. Deficiencies in potassium also contribute to the susceptibility of the so il to leaching Stalland, 2006. Potassium and nitrogen work together to support optimal uptake of nutrients Stalland, 2006. Potassium also is involved in production of amino acids, chlorophyll formation, starch formation, and sugar transport from leav es to root LaMotte, 1994. Aluminum: Aluminum is widely distributed in nature, and in some plants can be toxic LaMotte, 1994. In excess, aluminum can have significant impact on soil quality. Aluminum is common in acidic soils. As the majority of trop ical soils are acidic, it is interesting to evaluate their relationship. Iron: Although total iron in soil may be abundant, only a small portion is used by the plant. Solubility and mobility are the factors behind iron deficiencies in the plant LaMotte , 1994. Once the iron is absorbed it can act as a catalyst in the formation of chlorophyll, and is required in many of the plant s oxidation reduction reactions LaMotte, 1994. RESULTS Forest in the San Luis valley showed a neutral pH of 7.2. This rat ing is similar to Andisols studied in tropical Mexico but is generally high compared to tropical lowland soils, which range from 3.7 to 6.5, with Ultisols around 4 Martinez Sanchez and Sanchez Bertran, 2003. In general, tropical forest Andisols are inte rmediate in total Nitrogen, low in Phosphorus, low in Potassium but typical in Aluminum and Iron compared to other tropical soil types Martinez Sanchez and Sanchez Bertran, 2003. The Nitrogen levels had a mean of 36.65 parts per million, and the mean Ph osphorous was high with 100 parts per million. The mean Potassium was lowest of the four sites with 93.35 parts per million. And both the Aluminum mean 2.5 ppm and Iron mean 3.5 ppm levels were low. Coffee grown in the area had soil that differed fro m forest soil in a number of ways. pH was slightly more acidic than the forest soil, as pH 6.3. Nitrogen and Phosphorus were lower than in forests, with average values of 28.35 parts per million Nitrogen, and 83.35 parts per million available Phosphorous . The Potassium levels were lower than any other site with a mean of 93.35. The parts per million levels of Aluminum and Iron were notably higher than any other site. The mean values were 28.35 for Aluminum compared to the 2.5 parts per million in the forest, and 6.65 for Iron.
Cow farm had the greatest overall difference of nutrient levels from the forest. The cow farm showed the lowest pH with 5.4, which is highly acidic. The Nitrogen levels were highest with a mean of 66.65 parts per million, whic h is nearly double the amount found in the forest 36.65. The Potassium levels were also significantly higher than the other sites with a mean of 196.65 parts per million which is especially higher when compared to the mean of 93.35 of the forest. The Phosphorous levels were also lowest at 51.65 parts per million practically half of the forest s mean of 100. The Aluminum mean 3.35 and Iron mean 4.15 levels were not notably dissimilar compared to the organic farm and forest level. Organic farm t ests results appeared to have the closet relation to the forest results. The pH level was 7.2 closest to the forest pH of 7. The two had the same Phosphorous means of 100 parts per million, and the low levels of Aluminum mean 3.5 ppm and Iron mean 2 .5 ppm were very close to similarly low levels of Aluminum and Iron in the forest. The organic farm shared certain similarities with the coffee farm having the same Potassium mean of 120 ppm, and a mean Nitrogen level of 26.65, near that of the Coffee fa rm. Comparing land uses , soil from organic farms most closely resembled forest soils, cow pastures showed the greatest change in soil mineral composition and coffee plantations showed dramatic increases in Aluminum and Iron, which are generally toxic to plants. Only organic farming maintained a neutral pH, all other land uses created more acidic soils. Cow pasture had much more acidic soils, pH 5.4, while coffee was less acidic at 6.3. Cow pasture also had the biggest change in nitrogen from forest and other land uses. Cow pasture had a mean of 66.65 ppm, which was twice the nitrogen level of other land uses and nearly twice the forest nitrogen. Likewise, cow pasture had far more potassium. Cow pasture had less phosphorus, unlike other land uses that were nearly equal to forest levels. Coffee differed from forest and other land uses most dramatically in the high levels of Aluminum and Iron. See Figures 1 6. DISCUSSION The relationships seen in this study support the importance of recognizing how different agricultural practices affect the land in different ways. For example, the practices used with the organic farm had very minimal impact on the soil when compared to the area s most pristine, humanly untouched, forest soil. The greatest impact to the soil in terms of soil nutrient composition change was caused by the cow pasture. These heavier methods of agriculture can be dangerous to the future of the soil. Intensive uses, such as cattle farming, bulldozing and crop burning, degrade the produ ctivity of the soil for future land uses Buschbacher et al., 1988. In many cases the degradation is so significant that once farmed lands are abandoned, their soils are effectively sterile Matson et al., 1997. The cow pasture had a significant impact on the soil s composition. The soil in some areas experienced a depletion in nutrients, and others experienced an appreciation. The lower pH level meant a lower level of acidity in the soil. This affects the growth and
overall activity of growth of the organisms living in the soil. The alteration of the soil s chemical composition along with its physical and biological processes can limit the species able to live within it, and do so on into the future. Older, more nutrient poor tropical soils that have been abandoned demonstrate the soil s inability to maintain long long term livestock production Martinez Sanchez & Sanchez BetrÃ¡n, 2003. This is mainly due to the caused erosion and leaching of the soil s nutrient minerals. Low levels of Nitrogen, Po tassium and Phosphorous can limit the future productivity of a pasture Martinez Sanchez & Sanchez BetrÃ¡n, 2003, the results for this test only showed a decrease in Phosphorous levels, both Nitrogen and Potassium were significantly higher than the other s ites. The higher levels of Potassium are related to the lower acidity levels, as well as a favorable influence of grass on potassium cycling to the soil s surface compared with forest vegetation Reiners et al. , 1994 . The high levels of Nitrogen are prob ably due to the heavy content of cattle urine and excrements which return ~80% of the Nitrogen removed in the grasses eaten by the cows. And through the continuous trampling of soil, reducing large pore spaces and increasing bulk density, infiltration and percolation rates are affected, in particular altering nitrogen cycling causing slower rates in plant N uptake Reiners et al., 1994. What might also account for these results may be due to the specificity of the soil. Though tropical soils generally sha re the similar characteristics, various types of soil exist and certain types are more suitable for sustaining cattle. Pastures appear to be viable in the long term only on fertile soils like Andosols Martinez Sanchez & Sanchez BetrÃ¡n, 2003. The soil i n and around the Monteverde region has been classified as Andosols, clays over limestones and alluvial soils. This is beneficial, as it has been shown that moderate levels of fertilization, pastures can be kept at a high level of production Martinez Sanc hez & Sanchez BetrÃ¡n, 2003. Active pastures tend to be more fertile than forest soils Reiners et al., 1994. Having high aluminum and iron levels can be quite toxic to plant health and the coffee farm soil demonstrates the threat of such toxicity with lon g term agricultural use. This poses particular concern in the future of tropical agriculture, and biodiversity. Coffee production continues to grow rapidly throughout Latin America as the conditions are ideal in tropical mountains at mid elevation. Frequen tly, coffee crops replace tropical and subtropical moist/wet forests, on poor soils. In addition, these poor soils generally have high possibility for erosion and are high areas of biodiversity. Combining these conditions with the development of high lev els of iron and aluminum greatly reduces the fertility of the soil. This makes regeneration and reforestation on lands once farmed for coffee difficult. Though reforestation and regeneration have proven challenging in abandoned agricultural land, effor ts are being made, and through experience, knowledge of what works, and what does not is being gained. By looking at the results of this study through a wider lens, some conclusions can be made. Organic farming appears to have the lowest impact on origin ally existing soil nutrients and is most similar to the conditions of the forest. Cow pastures, though significantly alter levels of certain nutrients, can actually make soil more fertile. With proper treatment with fertilizer, these areas can maintain c attle and productivity for years. Long term coffee farming on an area has the potential of being perhaps the most detrimental. By taking over originally forested areas, erosion risks are greater, and higher levels of biodiversity are threatened. The hig h levels of
aluminum and iron leave the soil more toxic, and reduce opportunity for successful productivity in the future. Though positive efforts towards regeneration and reforestation in abandoned agricultural land, such as planting native seedlings an d implementing bird perches, continue to be made, they cannot bring forests back to life if the soil beneath has been too heavily depreciated. This would be the worst outcome for agriculture. Soil is the base upon which so much of life depends. Poor pra ctices of farmers, and excessive human consumption for certain tropical products, could lead to decreases in surrounding biodiversity and soil devoid of necessary nutrients. Changes need to be made for future agriculture to be productive alongside the succ ess of future biodiversity. Smarter choices need to be made concerning farming techniques, soil specific farming needs to be implemented whenever possible, and certain crops need to be cultivated less as to not compromise what deserves to be offered equal ly to generations to come. ACKNOWLEDGEMENTS Thank you to Alan Masters who continued to be patient, helpful and flexible throughout my many project adjustments and alterations. Thank you to Milton Brenes Salazar w ho never was hesitant to help me with a ll my projects and offer new ideas. Thank you to Pablo for general assistance, and thank you to Taegan for kindly explaining how to write a scientific paper. And thank you to the farmers of Finca la Bella in San Luis. LITERATURE CITED AMELUNG, T., & DI EHL, M., 1992. Deforestation of tropical rainforests: economic causes and impacts on development. Mohr, Tubingen, Germany. ANDERSON, J.M., & INGRAM, J.S.I. 1993. Tropical Soil Biology and Fertility: A Handbook of Methods, Second Edition. CAB Internatio nal. Wallingford, UK. BLUM, W.H. 1998. Basic concepts: Degradation, resilience, and rehabilitation. p. 1 17. In R. Lal et al. ed. Methods for assessment of soil degradation. Advances in soil science. CRC Press, Boca Raton, FL. BUSCHBACHER, R., UHL, C ., SERRAO, E. A. S., 1988. Abandoned Pastures in Eastern Amazonia II Nutrient Stocks in the Soil and Vegetation. Journal of Ecology. 76, 682 699. GREENLAND, D.J., WILD, A., & ADAMS, D. 1992. Organic Matter Dynamics in Soils of the Tropics From Myth to Complex Reality. Myths and Science of Soils in the Tropics. 29:17 34. HOLL, KAREN D . 1999. Factors Limiting Tropical Rain Forest Regeneration in Abandoned Pasture: Seed Rain, Seed Germination, Microclimate, and Soil. HOLL, KAREN D., LOIK, MICHEAL E., L IN, ELEANOR H., SAMUELS, IVAN A., 2000. Tropical Montane Forest Restoration in Costa Rica: Overcoming Barriers to Dispersal and Establishment. Restoration Ecology Vol. 8 No. 4, pp. 339 349. Biotropica 312: 229 242. LAMOTTE SOIL HANDBOOK, 1994. LaMotte C ompany. Chestertown, MD. LARSON, W.E., & PIERCE, F.J. 1994. The dynamics of soil quality as a measurement of sustainable management. P. 37 51. In J.W. Doran et al. ed. Defining soil quality
for a sustainable environment. SSSA Spec. Publ. 35. SSSA and ASA, Madison, WI. MARTINEZ SANCHEZ, J.L., & SANCHEZ BELTRAN, S. 2003. The effect of time of use of tropical pastures on soil fertility and cattle productivity. Ecotropicos 161:17 26. MATSON, P. A., PARTON, W. J., POWER, A. G., SWIFT, M. J. 1997. Agr icultural Intensification and Ecosystem Properties. SCIENCE. Vol. 277. REINERS, W.A., BOUMAN, A.F., PARSONS, W.F.J., KELLER, M. 1994. Tropical rain forest conversion to pasture changes in vegetation and soil properties. Ecological Applications. 42pp. 363 377. RICHARDS, P.W. 1981. The Tropical Rain Forest. University Press, Cambridge. SANCHEZ, P.A., 1976. Properties and management of soil in the Tropics. John Wiley & Sons, New York, New York. SMITH, NIGEL J. H., WILLIAMS, J.T., PLUCKNETT, DONALD L., TA LBOT, JENNIFER P., 1992. Tropical Forests and their Crops. Cornell University Press, Ithaca and London. STALLAND, KATIE. 2006. Different Agricultural Management Practices Concerning Soil Fertility: case studies of six rural Monteverde farms. CIEE, Spri ng. University of Wisconsin Madison. TERBORGH, JOHN, 1992. Diversity and the Tropical Rain Forest. Scientific American Library, New York. WANDER, MICHELLE M., WALTER, GERALD L., NISSEN, TODD M., BOLLERO, GERMAN A., ANDREWS, SUSAN S., CAVANAUGH GRANT, a nd DEBORAH A., 2002. Soil Quality: Science and Process. Agron J. 94: 23 32. http://soils.usda.gov/technical/classification/orders/andisols.html.
0 1 2 3 4 5 6 7 8 Coffee Cow Pasture Organic Farm Forest pH Level Site 0 10 20 30 40 50 60 70 80 Coffee Cow Pasture Organic Farm Forest Nitrogen parts per million Site FIGURES FIGURE 1. Soil pH for different land uses and forest in San Lui s de Monteverde, Costa Rica. Three samples were taken per land use and analyzed using LaMotte soil tests. Coffee 6.3; Cow 5.4; Organic 7.2; Forest 7. Standard error bars are shown. FIGURE 2. Soil nitrogen content for different land uses and forest in San Luis de Monteverde, Costa Rica. Three samples were taken per land use and analyzed using LaMotte soil tests. Coffee 56.7; Cow 133.3; Organic 53.3; Forest 73.3. Standard e rror bars are shown
0 20 40 60 80 100 120 Coffee Cow Pasture Organic Farm Forest Phosphorous parts per million Site 0 50 100 150 200 250 Coffee Cow Pasture Organic Farm Forest Potassium parts per million Site FIGURE 3. Soil Phosphorous levels for different land uses and forest in San L uis de Monteverde, Costa Rica. Three samples were taken per land use and analyzed using LaMotte soil tests. Coffee 166.7; Cow 103.3; Organic 200; Forest 200. Standard error bars are shown. FIGURE 4. Soil Potassium levels for different land uses and forest in San Luis de Monteverde, Costa Rica. Three samples were taken per land use and analyzed using LaMotte so il tests. Coffee 240; Cow 393.3; Organic 240; Forest 73.3. Standard error bars are shown.
0 10 20 30 40 50 60 Coffee Cow Pasture Organic Farm Forest Aluminum parts per million Site 0 1 2 3 4 5 6 7 8 Coffee Cow Pasture Organic Farm Forest Iron parts per million Site FIGURE 5. Soil Aluminum levels for different land uses and forest in San Luis de Monteverde, Costa Rica. Three samples were taken pe r land use and analyzed using LaMotte soil tests. Coffee 56.7; Cow 6.7; Organic 6.7; Forest 5. Standard error bars are shown. FIGURE 6. Soil Iron levels for different land uses and forest in San Luis de Monteverde, Costa Ri ca. Three samples were taken per land use and analyzed using LaMotte soil tests. Coffee 13.3; Cow 8.3; Organic 5; Forest 6.7. Standard error bars are shown.
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Impactos de la actividad humana sobre la calidad del suelo tropical en relacin con la productividad futura de la tierra y la biodiversidad
Impacts of human activity on tropical soil quality in relation to future land productivity and biodiversity
The high rates of tropical forest clearing followed by intensive agriculture may significantly degrade the soils original nutrient content and chemical composition, reducing future productivity and future restoration efforts. Land use impacts were determined by collecting soil samples from four sites in San Luis, Costa Rica. Three areas presented different agricultural uses, and the fourth was an area of forest, comparatively untouched by human activity. To evaluate existing nutrient levels, six tests were conducted from three soil samples from each site: ph, N, P, K, Al and Fe. Trends were found in that the site with the heaviest land use experienced the most change in nutrient levels compared to the forest soil. The three different agricultural areas displayed differing results, even as they were all within the same farming community, no more than 15m from one another.
Las altas tasas de deforestacin en los bosques tropicales debido a la agricultura pueden degradar significativamente el contenido original de los nutrientes y la composicin qumica de los suelos, reduciendo la productividad futura y los esfuerzos de restauracin. Los impactos del uso del suelo fueron determinados mediante la recopilacin de muestras del suelo en cuatro sitios en San Luis, Costa Rica.
Text in English.
Agricultural intensification--Costa Rica--Puntarenas--San Luis
Intensificacin agrcola--Costa Rica--Puntarenas--San Luis
Tropical Ecology 2008
Ecologa Tropical 2008
t Monteverde Institute : Tropical Ecology