Plant samples have to be taken in such a way that should represent entire gradient of the slope since the growth of plants will be hugely dependent upon slope gradients vis-a- vis orientation of sun affecting exposure of length of photoperiod .

In slopy lands, you have to be doubly careful that crop performance evaluation has to be on the basis of hill top, plateau and valley or base of the slope , could be geomorphologically piedmont and pediment surface ...

Collection of plant samples on farmers field on slope depends on the following:

1. Different homogeneous growth area on visual observation

2. Distinct differences in crop growth appearance

3. Based on elevation

4. Based on marshy spots.

Plant samples have to be taken in such a way that should represent entire gradient of the slope since the growth of plants will be hugely dependent upon slope gradients vis-a- vis orientation of sun affecting exposure of length of photoperiod .

plant samples should be collected based on gradient of slope

Thanks much for all your kind recommendation! Actually what I am thinking is that whether any standard for determining the number of samples in each farm in slope land? For instance with the farm area of 5000 m2, with 57 rows of cowpea, the shape of the farm is not important, so how many samples can we decide to take?

Dr. Thanh, in that case to determine the number of samples you have to know the following things :

1. Differences in elevation from top to bottom.

2. The horizontal distance from the highest to the lowest.

Then accurately you may calculate how many samples you need to collect to minimize the effect of slope.