The results pave a pathway for further experimentation and the possible improvement of maize yield in the Maputaland area. They show major deficiencies exist in the soils. It would seem from the experiment that the solution to the poor crop growth is the overall application of artificial fertilisers, which would be primarily nitrate based.

There are a number of problems with this:

• Commercial fertilisers are too expensive for subsistence farmers
• The large amount of leaching which occurs in the sand means that any fertiliser applied would quickly pollute the groundwater. This could lead to health problems and would certainly be an ecological disaster. This would also mean that a very large amount of fertiliser would have to be used to have a significant impact.
• To be truly effective the fertilising would probably need an irrigation system to dissolve it. This would speed leaching, be even more expensive, and could cause salinisation problems.

Some other method is then needed to increase the nutrient content of the fields. The mass application of animal manure is also ruled out by the second point above and by the fact that most livestock grazes freely during the day, so their manure cannot be collected. This does not rule out individual farmers carrying out small scale applications, which would help their crops. Another benefit of this would be the increase of humus content of the sand, allowing it to hold more water and minerals.

The answer seems to be, therefore, the use of legumes. At the moment two legumes are grown as food plants, peanuts and a local bean called "imbumbe". Some people plant peanuts between maize plants as they require some shade from the sun and provide nitrates for the maize. Imbumbe is not grown very widely because of the time it takes to cook it. An education scheme could teach the local people the benefits of growing legumes to their future crops. Most crops in the area are grown in the beginning of summer when the rains come. The rest of the year the fields lie fallow. It may be possible to introduce a drought resistant legume into the area which could grow in the fields during this period, and increase the nitrate content of the soil. These could also be used as a fodder plant for cattle before the fields need to be cleared, this would clear the ground and increase the health of the livestock.

Because of the low water content of the soil very little plant matter decays. This means that the soil has a low humus content and can therefore not hold much water. Unfortunately this means that it is difficult to just leave dead plant material and allow it to decay as it would take a number of years. This is why the local farmers burn the fields to clear them, releasing vital minerals into the air.

Another possible solution is the development of hybrids which could grow well with lower concentrations of essential minerals. This is possible but there is a problem with hybrids, they loose their vigour if replanted from seed. This means fresh seed has to be provided each year. Though this is what is done by agribusinesses across the world it costs to much for subsistence farmers to do.

The answer then is a type of maize which has these properties but breeds true. At present one option may be a genetically modified maize, which could be used the world over if developed. Though this science is still controversial it may be widespread in the future. One such modification which would be very useful to farmers everywhere is the introduction of nitrogen fixing nodules to maize’s roots. If Rhizobium from legumes could be introduced into other crops the need for nitrate fertilisers would be reduced.

As always the most significant of these is time. The first crop was in a cold room and died after a minimum amount of growth. This meant that the backup crop had to be grown and measured in a very short time, giving only nine readings over eleven days before an infection killed many of the plants. The unidentified infection (probably a stem rot fungus like Pythium) affected over 50% of the plants by the twelfth day (those affected up to day 11 are highlighted in Raw data)

A major assumption that the ground water composition would accurately reflect the soil water composition was made. The recipe for the Maputaland solution was based on this. If this is not so the results for that nutrient solution will not actually be correct. This is quite possible as, though there is a significant amount of leaching in the sands, most ground-water will not support plant life well. For example, if there was as much nitrate in groundwater as in the complete nutrient solution it would be well above WHO health guidelines.

One of the essential minerals required for plant growth is phosphorus, yet this was not included in the chemical analysis of the ground water. This means that a phosphorus deficiency which does not actually exist in real life may exist in the experiment. On the other hand less phosphorus may occur in the soil than was added as part of Ca(H₂PO₄)₂ in the nutrient solution.

The light bed used was shorter than the span of plants so it was placed centrally. This could lead to extra lengthening in the plants at each end of the rows as they grow towards the light. This may have been the case with the control, but the Maputaland plants were at the other end and they did not show any extra growth or signs of etiolation. A second problem with the light may be that it was on 24 hours a day. Though this should boost growth it may interrupt the plant if it is photoperiodic. As all the plant were subjected to this it should not affect the findings of the experiment.

The humidity of the growing room was very high, almost 100%. This may have limited transpiration, which then slows the plants’ transport of water (because transpiration is used to draw water up xylem). The plants did attempt to avoid this problem by using guttation, a major use of energy just expelling water. A second effect of the warm temperatures and high humidity is that they are perfect conditions for fungi, increasing the chance of infections. This may be why the plants succumbed to such an infection. As above the fact that all the plants had this problem means it does not affect the findings.

The mineral concentrations of the Maputaland and complete solutions where compared in the Reasons for... section. Unfortunately the concentrations in the complete solution are excesses so as to be certain that all plants have enough minerals. This means the comparison made will probably exaggerate any deficiencies.

The same experiment could be repeated over a longer period of time, this would show the deficiencies’ effects much better as there would be time for more differences in growth and more deformities to develop.

Maize could be grown in the Maputaland solution but with various minerals at excess levels. This may conclusively show if one specific mineral is responsible for the poor growth. If not then combinations of minerals could be tried.

This could also be done in field tests in the area using applications of mineral solutions. This would have the advantage of having all the conditions correct, including the mineral composition of the soil water.

As observed in another section many of the local plants grow well, these could be tested to see why they are not affected by the mineral deficiencies. If they have a specific mechanism by which to do this it may be possible to use this to increase maize yields by genetically engineering this capability into it.

Alberts, B., Bray, D., Lewis, J., Raff, M., Roberts, K., Watson, J. D.. Molecular Biology of the cell, 2^nd edition, 1989. Garland Publishers, p359-361, p371-2

Devlin, R., Witham, F. Plant physiology, 4^th edition, 1983. PWS Publishers, p392-3

Encarta 97 Encyclopedia. Maize, 1996. Microsoft

Fogg, G. The growth of plants, 1963. Penguin, p93

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Roberts, M., Reiss, M., Monger, G., Biology: Principles and Processes, 1993. Nelson,p122-124, p131, p140

Still, D., Qhinebe, E., McCartan, M., Draft report to Siwelimpilo on the support of community based water supply in Maputaland. 1993. CSIR

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Nutrient deficiencies in soils of the Mseleni area, Kwazulu-Natal. - Justin Pooley, University of Cape Town
This study constitutes a baseline epidemiological investigation into the nutrient status of soils in the Mseleni district of Kwazulu Natal, where nutrient deficiencies have been implicated in the etiology of an endemic disease. Mseleni Joint Disease (MJD) is a crippling, osteo-arthritic condition which afflicts an unusually high proportion of the inhabitants of this district. Home-grown produce and indigenous plants, which form the basis of the local diet, may be nutritionally inadequate due to soil-related nutrient deficiencies. In spite of this, and the fact that epidemiological studies have been successfully utilized to elucidate the etiology of similar diseases elsewhere, studies to date have not included soil chemical investigations....