野菜栽培における機械除草の効果について

第3報 雑草競合下の作物生長モデルの開発と秋作ハクサイへの適用例

抄録

Improved plant growth model under the competition between the plant and weed was tried to develop in order to expect the maximum plant yield with the minimum labor.
Following differential equation was formularized as the plant growth model which describes basically logistic curve.
dy/dt={M-a·y+f(y)}y{1-ho(y)/r·g(t)/go(t)}
where,
y: the weight of the plant
t: time from the planting
M/a: estimated maximum growth weight, ye
f(y): collection term of quadratic equation of y approximated by the expression of b (y-c) (y-d)
ho(y): the inhibition function of the weed approximated by the expression of u(y-v)(y-ye)
r: the relative growth rate, M-a·y+f(y)
g(t): the weight of the weed approximated by the expression of A·t^B
g_o(t): the weight of the weed at non-weeding treatment plot approximated by the expression of Ao·t^B_O
Various optimum parameter values were obtained from the estimated plant growth values decided on the growth data of chinese cabbage cultivated in fall, 1979 to input in to the plant growth model equation and caluculate by the electronic computer using the solusion of the Runge-Kutta method for evaluating the numerical values of differential equation.
The caluculated value of the each weeding treatment plot agreed well with the estimated value of it, however, measured value of the mechanical weeding treatment plot was rather smaller than the caluculated value of it. This is caused by the existance of a lot of plant-spacing weed which was not able to be removed by the machine and inhibited the plant growth more seriously. a lot of plant-spacing weed which was not able to be removed by the machine and inhibited the plant growth more seriously.
The growth rate of each weeding treatment plot described mountaineous curves which had maximum values at the point of about 60th day after the planting, and then there were scarecely difference of the two between the three-time weeding treatments and the four-time treatments by the machine.
The acceleration of the plant growth which is obtained from the differential calculus of the plant growth rate was larger at about 35th to 55th day after the planting. Therefore, the precision weeding treatment at this time may bring the increase effect of the plant yield.
The opimum weeding operation system in this case was as follows;
21th day after the planting-mechanical
35th day after the planting-manual
49th day after the planting-mechanical
which brings 5610gf/0.6m² of the plant yield. This is more than 99 percent of 5650gf/0.6m² of the plant yield estimated from non-weed-four-time manual weeding treatment plot and 25 percent increase of 4460 gf/0.6m² of the plant yield estimated from non-weeding treatment plot. It is author's conclusion that this plant growth model discussed here is the effective method to estimate the suitable weeding time and optimum weeding mean as the objective function of the maximum plant yield, and ultimately contributes to the improvement of weeding operation.