Researchers investigating the effects of various arable farming techniques noticed differences in soil moisture and the organic matter between fields that were conventionally farmed and those that used conservation agriculture. Conservation agriculture is a cropping system based on techniques such as:

minimal soil disturbance (low or no-tillage systems) maintenance of permanent soil cover (e.g. through crop residue and cover crops).

The researchers decided to test whether their initial observations were accurate.

They sampled 10 areas that used conservation agriculture and 10 areas that used conventional farming. The same crops were grown in all the areas. For each area the soils were sampled and analysed for moisture, for bulk density and for organic matter content using the loss on ignition method.

The results of the investigations are shown in the Table below.

Soil sample number	Soil moisture (%)	Soil bulk density (mg m-3)	Soil organic matter (%)
Conventionally farmed
1	8.9	0.95	1.2
2	9.6	1.1	1
3	10.1	0.87	2.1
4	8.2	0.99	1.7
5	7.5	0.98	3.8
6	9	0.94	1.9
7	11.8	0.83	2.3
8	12.4	0.87	2.4
9	8.7	0.88	2.1
10	13.2	1.09	1.5
Conservation farmed
11	15.7	0.98	2.9
12	18.2	1.03	4.1
13	19.9	0.85	3.3
14	11.3	0.81	4.8
15	16.2	0.95	4.2
16	12.5	0.99	3.9
17	14	1.09	3.7
18	17.6	1.11	2.8
19	15.6	1.01	3.1
20	14.7	0.98	4.2

Using the information presented above, statistically analyse the differences in soil moisture, bulk density and soil organic matter using the Mann-Whitney U-test.

Use your analyses, and knowledge of this statistical test, to answer the questions that follow.

Qa. (3 marks) State the three null hypotheses that are being tested in this exercise.

Qb. (2 marks) Why is the Mann-Whitney U-test the appropriate statistical test to use in this investigation?