In the past few thousand years, three major problems have plagued farmers: declining soil nutrients with each successive crop, the ravages of insects and the encroachments of weeds on the crops.
幾千年來，令農家頭痛的三個問題，除了土壤耕種後會失去肥分，就是動物昆蟲會吞食作物，以及植物野草侵佔田地。