The land in the rainforest is the foundation of a complex ecosystem. In characterizing it, one must reveal its unique chemical and compositional traits. Furthermore, since the land is so critical for the health of the rainforest, the land’s own health must be characterized and subsequently monitored. When we speak of the health of the land, we are referring to its ability to sustain biological dependents. In some areas of the rainforest, the land's health is in jeopardy.

            The rainforest is one of the most complex ecosystems on the planet, sporting massive biodiversity and plant density. However, somewhat ironic, is the fact that the land is some of the most infertile on the planet. Rainforest soils contain only a few centimeters of organic compound rich topsoil, and below that is cation poor, kaolin containing clay (Refer to Eva’s characterization). These two characteristics result in soil that is not only poor in nutrients to begin with, but is also poor in absorbing new nutrients. However, as poor as the soil is, it is evident in undisturbed forests that nature has found a way to cycle any available nutrients to create a self-sustaining ecosystem. It is in the sections of the forest which have been ravaged by man that we now concern ourselves with.

            The rapid deforestation currently occurring in the Amazon rainforests is not the result of a lack of suitable farmland but rather of the inefficiency of current agricultural methods. Although it may seem like mankind and nature can never coexist in harmony, this untrue. The current method of the slash-and-burn agriculture was at one time a sustainable technique. Slash and burn involves clearing a section of rainforest, fertilizing it by burning the preexisting plants, and then planting the desired crop. This method will be able to support only 2-3 years of production, after which the farmer leaves the field fallow and moves on to another plot of land. After approximately 25-30 years the farmer returns to the original field to burn the secondary growth forest and repeats the process.   Due to increasing population pressure, the fallow time has now been significantly. If these fields are planted with little or no nutrient input, yields of annual crops decline rapidly because of decreasing nutrient availability and weed encroachment, prompting farmers to clear another section of forest (Gotz Schroth, et. Al.) Clearly, current methods are not effective and continuing to use them will only result in further deforestation.

            A number of techniques of are used to prevent this loss of nutrients. The most popular of which is the use of fertilizers. However, in the context of rainforest soil, fertilizers offer little if any help. A large portion of the rainforest soil is, strangely enough, rich in Nitrogen. Therefore Nitrogen is not the primary deficient nutrient, rather organics are, and the addition of nitrogen into the soil will not affect crop yields. An alternative to traditional fertilizers is the use of green manure. Green manure is basically the use of decayed plant material as fertilizers. Although green manure is effective at increasing the organic compound level in soil, this benefit is decidedly short lived due to the inability of rainforest soil to retain nutrients. However there is another method that has much promise: Agroforestry.

            A promising solution is that of agroforestry. Taken directly from the statement found on the website of the World Agroforestry Centre, agroforestry is: “A dynamic, ecologically based, natural resources management system that, through the integration of trees on farms and in the agricultural landscape, diversifies and sustains production for increased social, economic and environmental benefits for land users at all levels.” In respect to the Amazon rainforest, agroforestry provides the possibility of sustainable agriculture with little external input (i.e. fertilizers). Agroforestry is basically the use of polyculural fields consisting of trees and intercrops. Agroforestry sustains crops yields by reducing nutrients lost though runoff and increasing organic matter content in addition to other nutrients in the soil (Chander, K). In some cases the trees themselves provide another crop, though the fruit or products they produce.

            Although the Amazon rainforest is not a watershed, due its high levels of precipitation and thin top soil layer, it has similar runoff patterns characteristic of watersheds. In a paired watershed study consisting of agroforestry (trees plus grass buffer strips), contour strips, and control treatments, it was shown that agroforestry reduced total phosphorous loss by 17%, total Nitrogen loss by 20% and effectively reduced nonpoint-source pollution in runoff (Udawatta, et. Al.). Editor notes: more data later…

            Studies have shown Agroforestry techniques to be effective at directly increasing the nutrient availability of the soil. For example one study (Chander, et. Al.) observed the soil organic matter, microbial biomass and enzyme activities in a tropical agroforestry system. In this system 12 yr old Dalbergia sissooo (a N2 fixing tree) plantation was intercropped with a wheat and cowpeas. This plantation was compared with a control plantation that did not have the tree treatment. It was observed that the levels of organic carbon, total Nitrogen, microbial biomass Carbon, basal soil respiration and activities of dehydrogenase and alkaline Phosphatase were higher in the treatment with tree-crop combination than in the treatment without the trees. Editor notes: more data later…

            Although agroforestry presents itself as a possible sustainable agricultural method, there still a few issues that need to be resolved. Although trees aid the crops by providing them with increased nutrient levels, anytime multiple crops are planted in a single field there is competition.  In the same study that observed the tropical agroforestry system it was found that crop roots decreased with and an increase in tree density. This was due to the canopy of the trees shading the crops. Therefore further research is needed to determine the ideal distribution of trees and crops that would be most beneficial. Also different species of trees exhibit different affects on the soil. In one study (Gotz Schroth, et. Al.), it was found that annatto and cupuacu had favorable affects on nutrient availability in the soil in comparison to peach palm and Brazil nut. Further research is needed to determine exactly which combination of crops results in the best results.

 

More Editor Notes: I didn’t have access to some journals, the information will be incorporated later. For now enjoy this first version.

-Tri