Site-Specific Sowing - Precision in Crop Farming - page 173

high plasticity: site-specific control primarily can save in seed-costs;
low plasticity: site-specific control primarily can increase yields.

seed-density

Fig. 8.4 Influence of seed-density on yield depends on crop plasticity (schematic curves)

8.2 Seed Distribution over the Area

Precision farming also implies precision in the seed distribution over the area.
The area per seed is the product of row spacing and mean seed distance within
the row. With all crops, presently row spacings are much wider than seed
distances within the rows. For wheat - the most common crop on earth - a row
spacing of about 12 cm and a mean seed distance within the row of only 2-3 cm
are frequently used. Thus the plant distances perpendicular to the row directions
are about five times the distances within the rows. The situation is similar with
most other crops.
There are no indications that plants grow better when the distances to its nearest
neighbours in the row direction are smaller than in the direction perpendicular to the
rows. On the contrary, research at many places has shown, that ceteris paribus
decreasing the row spacing and accordingly increasing the seed distances within the
row improves growth of plants (Cox and Cherney 2011 ; Heege 1993 ; Heege and
Billot 1999 ; Lambert and Lowenberg-DeBoer 2003 ; Neumann et al. 2006 ). Probably
plant distances should be optimized irrespective of spacial direction. This means
that for precision sown crops , ideally the plants should be arranged in the pattern
of squares (row spacing equals mean seed distance within rows) or even better
theoretically in the pattern of equilateral triangles (Heege 1967 ).
For bulk drilled crops , reducing the row spacing to the mean distance of
seeds within the rows too would result in a very substantial improvement of the
arrangement of plants. However, because of the irregular seed distances within
rows, in this case the theoretical optimum in plant arrangement still would be not