From the link;
Hemp plants have few insect enemies, and respond to most soil types. They have a huge potential to be grown organically - without the use of chemical pesticides, fungicides and fertilizers. There is also no need for genetic modification (GM) of these plants - they already have the desired characteristics.
The plants are very fast growing - this means that they soon swamp out weeds. They also have very few pest enemies, especially so in North America and Canada. They tend to attract a larger proportion of pests in Western Europe, although still comparatively fewer than traditional crops. Research in Holland suggests that fungal diseases and pests can be reduced in traditional crops if grown in rotation with hemp.
Hemp has also traditionally been used to stabilize the soil in regions where there is a high chance of soil loss, for example upon the slopes of the mountains of the Himalayas. The plants have very penetrative roots. The main tap root can grow up to 12" deep in just 30 days. There is also a system of finer lateral roots which disperse themselves through the subsurface soil over 7-8", providing further stability.
Hemp plants are also wildlife friendly. Monoculture tends to lead to low levels of wildlife, particularly due to the loss of hedgerows and suitable habitats. Hemp plantations on the other hand have been shown to be beneficial to animals. Montford and Small (1999) found that hemp is biodiversity friendly in terms of species numbers and in competition of nutrients with wild land. Hemp plantations especially increase the numbers of birds. As many bird keepers will be aware, hemp seed is by far their favourite food. Scientific studies have shown that birds with a staple diet of hemp seeds can live up to 20% longer, be much healthier, have more lustrous feathers and produce more off-spring. The plant has the potential to resolve the problems associated with conventional farming.