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冯世义在1984年第1期《耕作与栽培》上撰文说,利用土地当量可判别间作套种与单作的增减产。如两种作物间套种,产量分别为M_1、M_2,单作时分别为m_1和 m_2,则其土地当量 T=M_1/m_1+M_2/m_2,若 T>1,即表示间作套种比单作增产,若 T<1即减产。以能量表示某一种植制度的产量,如小麦、玉米、红薯三熟制,其产量分别为x、y、z 斤。三种作物含碳水化合物、蛋白质、脂肪分别为 a_1、b_1、c_1,a_2、b_2、c_2,a_3、b_3、c_3。碳水化合物含能量为4.15千卡/克,蛋白质为6.65千卡/克,脂肪为9.40千卡/克。用 W_1、W_2、W_3分别表示
Feng Shiyi in 1984, No. 1 “farming and cultivation,” the article said the use of land equivalent can be used to intercropping intercropping and single crop increase or decrease. If the intercropping of the two crops yields M_1 and M_2 and m_1 and m_2, respectively, the land equivalent T = M_1 / m_1 + M_2 / m_2. If T> 1, , If T <1 that is cut. The energy output of a plantation system, such as wheat, corn, sweet potato three cooked system, the output was x, y, z jin. The three crops contain carbohydrate, protein and fat, respectively a_1, b_1, c_1, a_2, b_2, c_2, a_3, b_3 and c_3. Carbohydrates contain 4.15 kcal / g energy, 6.65 kcal / g protein and 9.40 kcal / g fat. W_1, W_2, W_3, respectively