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Is the poor growth of maize in the Maputaland area of South Africa caused by mineral deficiencies? |
Plan for the experiment:
Results:
Possible reasons:
Impact on the people of the Maputaland area:
Possible future experimentation:
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Abstract: Maize (Zea mays) was grown in Perlite and watered with a mineral solution which reflected the mineral concentrations of soil water in the Maputaland area. Its growth in height was compared with that of plants grown in a complete solution and in solutions deficient in sulphur, magnesium and nitrate. It was proved that a severe mineral deficiency of a number of essential minerals causes the stunting of maize in the Maputaland area. The Maputaland area is one of the most economically deprived areas of South Africa. A large percentage of the population survive by subsistence farming of maize. The maize in this area is stunted, has chlorotic leaves and very low yields.  There have been suggestions that this poor growth is caused by poor hybrids or a lack of soil moisture. I believe the reason for this is actually the mineral content of the soil. This is partly supported by observations that commercial hybrids of maize do not grow well in the area even if watered well. The soil is deep sand (up to 2000 metres deep!) which was laid down by falling sea levels. This sand formed into dunes which have been covered by unique dry sand forest and grasslands. Due to the low rainfall and fast drainage of this sand dead plant matter does not decompose very fast and the nutrients that do make it into the soil are often leached out. To increase the nutrients in the soil
the local, Zulu farmers usually burn the grass or woodland in a form of
slash and burn farming. This improves growth somewhat but it is still stunted
by normal standards. After a few years the available nutrients have been
used up or leached out of the soil and growth falls again. To grow maize
in this soil the seeds have to be sown about a metre apart, as opposed
to the couple of centimetres apart used in commercial maize farms on fertile
soils.
The pots will then be split into five groups of 16 pots and each labelled as to which nutrient solution should be used. Each group then contains 80 seeds. The pots will be placed in a growing room kept at around 25oC under a light bed of fluorescent tubes. Maize will not grow below 9oC or above 46oC. Its optimum growth occurs between 30 and 35 degrees (Street & Öpik, 1984). At 25oC vertical growth is fast enough to take a measurement each day. To be available for absorption by plants minerals have to be dissolved in water. It follows from this that the chemical composition of the soil water will reflect the nutrients normally available to plants (Street & Öpik, 1984). To do this experiment it is necessary to assume that, because of the massive amount of leaching in the Maputaland sands, the groundwater will have the same concentrations of minerals as the soil water. This may actually be the case as the water table in the area is often within 5 metres of the surface. (Still et al, 1993) An engineering firm doing work on wells in the area provided a chemical analysis of groundwater which included most of the minerals important for plant growth. From this it is possible to make a nutrient solution which reflects the mineral content of the Maputaland soil. Plants grown in Perlite, a sterile growth medium, and watered with the nutrient solution can be compared with those grown in similar conditions but watered with complete nutrient solution or with solutions which are deficient sulphur, magnesium or nitrates.
Recipes for the basic nutrient solutions
The deficient solutions have the compounds shown in the Substitute column used instead of those in the complete solution. For example, in the Sulphur deficient solution magnesium chloride is used instead of magnesium sulphate. To save space the solutions were made up at higher concentrations than needed and diluted to make the nutrient solution. For example, potassium chloride solution was made with 100ml of distilled water and two grams of KCl. Ten millilitres of this stock solution was used per litre of the nutrient solution. To maintain the correct concentrations in the final nutrient solutions the volume of the stock solutions will be subtracted from the volume of distilled water used. These recipes give these concentrations of minerals: Concentration of minerals in the nutrient solutions (mg/l)
The three deficient solutions were
chosen because their symptoms are similar to those shown by maize growing
in the Maputaland area and the amount of information available about the
effects of their deficiencies. Because of their importance in proteins
sulphur and nitrate cause stunting and structural deformities. Nitrate
deficiency also leads to necrotic patches and fewer and abnormal chloroplasts,
which causes chlorosis, because the protein is needed for chloroplast production.
Magnesium also leads to fewer chloroplasts. The most important use of magnesium
in a plant is as part of the chlorophyll molecules and as a cofactor for
many enzymes. Without these less photosynthesis takes place and the plant
is stunted by the lower energy production. This means they all show the
chlorosis and stunting shown in the Maputaland area. (F5.1
Reasons for... for a more detailed explanation of their effects)
To make a nutrient solution which reflects
the nutrient levels in the Maputaland area the groundwater analysis shown
on the next page was used as the basis of a recipe. By using each component’s
molecular weight it was possible to work out, by trial and error, a recipe
which fulfilled these specifications.
Chemical analysis of the Maputaland groundwater
was used to work out a recipe which contains these elements at the correct
concentrationswhere R = the mass of element required per litre (milligrammes) C = the mass of one mole of the compound containing the element (in grammes) P = the mass of the compound needed to provide the mass R (grammes per litre) M = the mass of the element in one mole of the compound containing it (in milligrammes) For example: 12mg/l of potassium is needed in the nutrient solution. The formula then works out like this:
By trial and error a recipe can be made up by working out a combination which give a level of minerals almost identical to the groundwater analysis. Recipe for the Maputaland solution
2.3 Measurement Once the mean height of the
maize plants reaches two centimetres the height of every plant can be measured
each day with a ruler (to the nearest half centimetre). This should be
done at the same time each day. Though this method is not extremely accurate
it is accurate enough to compare daily heights for a large number of plants.
The results will be recorded in a table and
typed into a spreadsheet. From this the average height for each nutrient
solution can worked out for each day, allowing the calculation of average
growths and comparisons.
2.4 Variables and their control:
There are a number of simple factors
that affect plant growth, as I will be testing the effect of available
minerals the other variables will need to be controlled as much as possible.
The experiment was already attempted
in a room where the variables were not as well controlled. After a month
of very poor growth and minimal germination the few plants died when the
room’s heating was turned off for a week. This meant a lot was known about
the different variables and their effects before this second plan was made.
The maize plants grown in the Maputaland
solution will be significantly stunted compared to those grown in a complete
solution and will have more deformities. This will prove that the poor
growth is caused by a mineral deficiency.
The other deficient solutions will
also cause stunting and deformities in varying quantities. |
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