Poor growth of maize caused by mineral deficiencies?

Is the poor growth of maize in the Maputaland area of South Africa caused by mineral deficiencies?

Plan for the experiment:
Equipment:
The nutrient solutions:
Measurement:
Variables and their control
Hypotheses:

Results:
Table of results
Graphs
Growth in the different solutions: Percentage germination:
Deformities:

Possible reasons:
Reasons for stunted growth and deformities:
Growth rates:

What caused the different germination rates?
What about the plants native to the Maputaland area?
Conclusions

Impact on the people of the Maputaland area:

Limitations:

Possible future experimentation:

Bibliography

Further Reading

Raw data

3. Method:

The plan was carried out with very few adaptations.

80 pots filled with Perlite
400 soaked maize seeds planted in the pots
Watered weekly with nutrient solutions as described above. Each group of 16 pots needed about 1.8 litres of solution a week.
Measurements taken as close to 24 hours apart as possible. This very hard to do so the times were not as regular as they should have been.

A fungal disease, possibly Pythium, caused wilting and then death in half the plants by the twelfth day of measuring. This meant measurements had to stop on day eleven.

4. Results

4.1 Table of results and Graphs of results

4.2 Growth in the different solutions

As you can see from the graphs, and the table of results, there are significant differences in the growth with different nutrient solutions. As predicted the growth in the Maputaland solution is much less than in the control, a height difference of 3cm in their final average heights. Sulphur, magnesium and nitrate deficient solutions produced similar growth patterns, as can be seen clearly from graph 6 where they often overlap. This is interesting as I assumed that the different deficiencies would produce quite differing growth rates as their roles in a cell’s biochemistry are generally different (F 5.1 Reasons for...).

By using the t-test it was possible to prove that there is a significant difference between the heights of plants in the different solutions.

T-values

Solutions compared

t-value

p value

Complete & Maputaland

14.830

< 0.001

Sulphur & Maputaland

5.230

< 0.001

Complete & Nitrate

7.366

< 0.001

Sulphur & Nitrate

0.364

>0.1

As you can see there is a statistically significant difference between plant heights in the Maputaland solution and in the complete. There is also a difference between heights in the sulphur deficient solution and in the Maputaland solution. A difference exists between the complete and nitrate deficient solutions. The sulphur, nitrate and magnesium deficient solutions are all similar, as shown by running the t-test on the results for the sulphur and nitrate deficient solutions.

The growth rate per hour was then calculated. To do this it was necessary to assume that the growth was constant between measurements and that exactly 24 hours passed between the daily readings (and 48 over the two Sundays). The difference between the daily readings was divided by twenty-four (or forty-eight) hours. Neither of these assumptions is totally correct so may account for some of the fluctuation that can be seen in graph 7. Though there is only a difference of one micrometre between the growth rates of the sulphur deficient solution and the Maputaland solution over eleven days this leads to a difference of 1.2cm in their final average heights.

Growth rate in m m/h

	Complete	Sulphur	Magnesium	Nitrate	Maputaland
27-Nov
28-Nov	40.32	33.17	35.52	24.71	30.11
29-Nov
30-Nov	46.24	41.96	37.99	41.20	39.50
1-Dec	26.06	5.36	17.24	13.89	20.31
2-Dec	32.71	21.48	22.55	29.70	1.51
3-Dec	9.86	8.61	7.56	9.11	17.81
4-Dec	10.66	7.77	13.27	4.51	-0.93
5-Dec	-1.91	-2.47	-4.95	2.58	6.08
6-Dec
7-Dec	-1.14	3.32	5.44	0.01	-3.14

mean	20.35	14.90	16.83	15.71	13.90

(F Graph)

A second thing that can be seen is that the graphs of growth show an S-shaped form as if something is limiting growth or the maize is reaching its final height. As they level off at such low heights compared to maize grown in natural conditions there must be something limiting the plants. This is probably the wilting disease described earlier though other possible factors are discussed in 5.2 Growth rates.

Thirdly, because of the large amount of data collected, the confidence intervals are small in this experiment, ranging from 0.42 to 1.26. This is useful as it shows that the results are consistent.

4.3 Percentage germination

Some interesting results were found by counting the number of maize plants which germinated in each group. This was unexpected as I assumed that germination would be unaffected by the deficient solutions.

Percentage of non-germination in different nutrient solutions

complete	no Sulphur	no Magnesium	no Nitrate	Maputaland	Mean
15	27.5	32.5	22.5	21.25	23.75

(F Graph)

4.4 Deformities:

Because of the shortness of the experiment there was little time for the development of deformities. Despite this some did form. These were in the plants growing in the Nitrate deficient and Maputaland solutions. A number of plants in each showed necrotic patches on their of the leaves. With the Maputaland solution the tops of some shoots were twisted and bent over into a spoon-like shape. Once they had this twisted form they stopped growing.