Wednesday, October 22, 2008
Assignment 1
A question was asked that if we greatly increase crop yields by genetic enhancement/breeding and/or management practices won’t we take too much from the ground and deplete mother earth? Please provide an answer to this question including whether you think it will deplete the ground or not and why you think as you state. For an example let’s say we increase the harvested dry matter yield of a biomass crop from 20,000 kg/ha to 50,000 kg/ha and this harvested material is converted into energy. Post your answer to this blog.
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9 comments:
If we largely increase crop yields, it seems that we take too much from the ground and deplete mother earth one day. However, in my opinion, our mother earth cannot be depleted forever unless our future generations bring all of these materials and themselves to other planet. Our mother earth has a large balance circle. A plant needs light from sun, water from earth and ions from earth to grow and most of the energy from light. If we improve the crop yields, it seems that we need more light, water and ions. However, the energy in plant will increase too. More energy will flow in the food chain. The more harvested crop from earth, the more energy will flow to the upper level. However, this energy at last returns back to the earth as the way of excretion or corpse one day. Obtain from mother earth and return back to it at last. Thus, our mother cannot deplete forever if these energy are flowing in the balance system of the earth.
Well, I am not sure that the question is scientifically valid! I mean why do you think the earth materials will be depleted? Earth is the biggest buffer system in the universe. The nutrients and the other materials from ground will never up. That because earth is in acontinuous cycle, and what is taking by plants is recycle by other means such as microorganism organic matter fixed in soil, decomposition organic matter from animal, and other organic waster. Add to top of that what is left by plant after harvesting will enter this cycle. The amount of organic matters that are fixed from fungi such as microrhyzae is much higher than any plant. So, I don’t think human will suffer from depleting the resources.
Abdullah Aqeel Said: Well, I am not sure that the question is scientifically valid! I mean why do you think the earth materials will be depleted? Earth is the biggest buffer system in the universe. The nutrients and the other materials from ground will never up. That because earth is in acontinuous cycle, and what is taking by plants is recycle by other means such as microorganism organic matter fixed in soil, decomposition organic matter from animal, and other organic waster. Add to top of that what is left by plant after harvesting will enter this cycle. The amount of organic matters that are fixed from fungi such as microrhyzae is much higher than any plant. So, I don’t think human will suffer from depleting the resources.
This is a good question! In my opinion, the answer all depends on the biomass crop that is used for energy harvest. Currently the use of cornstarch as the source of sugar (for bioethanol production) requires that an annual crop like corn be replaced after harvest and a new crop replanted for the following year. Using crops like this requires fertilizer, irrigation and plowing of the soil that can actually release a significant amount of CO2 into the atmosphere. In addition, the interval of time after the ground has been plowed but before there is substantial growth of the crop, can lead to erosion and depletion of the topsoil. Not to mention the competition that growing corn for fuel creates with the food supply, but that's another question entirely!
On the other hand, the use of perennial C4 crops like switch grass allows for the use of marginal agriculture lands and no requirement for fertilizer or irrigation. This is possible because these types of plants have very efficient water use due to their deep root system and superior form of carbon fixation. Therefore, perennial C4 crops can grow very well in warm, dry climates or in soils with high salinity. In addition, because they are being harvested strictly for their biomass and not starch accumulation, they can be allowed to senesce on the field BEFORE harvest. This allows for all the nutrients, particularly nitrogen, to move back into the root system that remains overwinter under the soil and consequently produces the new crop the following year. These types of plants can actually improve the quality of the soil, prevent erosion and sequester carbon while at the same time provide the raw material for biofuel production. Based on these characteristics, I would say that the use of the right crops (genetically enhanced or not) for energy production can actually be beneficial to the soil and the atmosphere.
I don’t think the mother earth will be depleted just by increasing crop yields. The major part of crop yield comes from photosynthesis: harvesting solar energy and converting water, absorbed from soil, and CO2, absorbed from the atmosphere, into biomass. The other parts of crop yield come from other minerals absorbed from soil. It seems like the more crop yield we get, the more we take from the earth. But the materials used to increase biomass are still kept on the earth. Some of them form the plant tissues, making the crop yield; the others simply participate the formation of other plant bodies. After harvested, the plant body parts are recycled: water evaporated and is recycled in the atmosphere and finally fall back to earth in the form of rain or snow; the organic materials are disassembled by microorganisms and returned into the earth. The crop yield part is recycled back to the earth by different approaches based on their usages. As in the example, the harvested biomass is converted into energy, which comes from the oxidation of carbohydrate, fatty acid or other organic molecules in the biomass. This oxidation process not only releases the energy stored in organic molecules but also produces CO2 and returns the carbon into the atmosphere. In the other usages, the biomass is assumed by human or animals, and converted into their biomass increases. Finally this kind of biomass is also disassembled by microorganism and recycled back to the environment. Thus this cycled process keeps all the materials used to increased crop yield on the earth and the earth will not be depleted simply by increasing crop yield.
Increasing crop yields does not necessarily mean that we will remove all of the nutrients from the soil. It all depends on the nutritional requirements of the plant and the nutritional content of the soil. Nutrients in the soil water are constantly in flux with nutrients bound to the soil colloids. If we remove some of these nutrients, then they will be replenished by the reserves, due to the principles of equilibrium. However, each soil is different. Many soils must be fertilized from the "get-go" to ensure desired yields of basically any crop grown on them. In this case, if we increase biomass then we will definitely have to fertilize more. Some soils have most of the nutrients that a plant needs. In this case, it would depend on just how much of the nutrients were there. If the nutrient content is low then one may have to replenish the nutrients by adding fertilizers.
Another thing to think about is water. Larger biomass plants often require more water, and all soils demonstrate different water dynamics. Some soils stay water logged and some stay dry. Most agricultural soils are in between these extremes. It is highly likely that increasing the biomass more than double (as suggested in the question) would increase the water requirements per/ha.
The higher biomass plants could actually be used to help improve the soil quality given that the cultivators are smart enough to use them wisely. One major component that increases soil quality is organic matter. If the crop being grown is going to be used for energy and we can use the entire plant for this energy, a "knee jerk" management plan would be to take the whole plant. This would be very foolish. As most of the Midwestern U.S. has seen, when we fail to manage soil organic matter, our top soils suffer. If the plants are enhanced to generate more biomass, then theoretically we can leave more behind. The organic matter could then act as a protective shield against erosion and eventually become incorporated into the soil matrix. Once in the soil matrix the O.M. will confer some desirable traits to the soil. O.M. is known to enhance soil structure and improve soil water content. It does this because it helps increase the porosity of the soil, so more air and water can be held in the same space when compared to a soil with less O.M.
All that being said, the answer to the question is indefinite and would depend on the all of the above factors. Most likely, increasing the biomass will require additional nutritive and moisture inputs. This would be especially true for micronutrients, which are often found in low concentrations in soils and are usually supplemented. Agriculture is a delicate balance of relying on the earth to provide most things and adding only as much as the plant needs. This can be tricky and has taken us thousands of years to finally get down to a science and we still have much more to learn. Investigating questions like these will only help us create a fuller picture.
Most of the biomass in plants come from the CO2 fixation through photosynthesis and only essential nutrients are taken from the soil by plant,I think regardless of the fact that you increased the biomass yield of your crop, if over the years your crop eats away on N from soil it will deplete the soil of N. But, if we think about it, most farmers would use fertilizers that would add back the N that has been taken from the soil. As a specific example in India, groundnut is mixedcroped with legumes, groundnut depletes soil of N but legumes add back the N because of the nitrogen fixing bacteria living in their root nodules. In my opinion having a field of monospecific crop year after year depletes some of the nutrients in soil like N,P,K, Ca, etc. But there are some crops that can give back the nutrients to the soil when they die and that is why most of the places, agricultural practices have led to having fields of mixed crops. Please refer to Florencia Montagnini, 2000for a specific example about having a mixed plantation in forests and its effect on soil fertility.
If net productivity is zero then no, mother earth will not be depleted by genetic enhancement of agriculture crops. If dry matter yield of a biomass crop is increased and converted to energy, this energy can be used, recycled and in theory returned to the earth. However, in my opinion, the chance of this energy being recycled to the exact point of harvest is highly unlikely. Therefore, the question of whether or not mother earth is being depleted depends on whether or not we sufficiently supplying external inputs to compensate for the increase in dry matter yield. As a whole mother earth is well equip to adapt to changes, but the site of production would need compensation for increased yield.
Answer would be no. The mother earth would not be depleted by crop production. Without adding fertilizer back, it would not possible for human to keep the current yield, not to say the increment. It is true breeding engineering and other method would increase the yield. But all would be limited by the nutrition. And people who want to get the 50,000 kg/ha yield must add the nutrition. So the usage and adding would be barely balanced.
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