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.

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Theoretical analysis for asking optimum amount of side-dressing application and its aplication to spring-sown chinese cabbage were conducted in order to obtain uniform product and higt quality yield by precisely controlling amount of fertilizer distribution according to the individual crop growth condition at the course of growth.
A crop fresh weight W was assumed to be the estimation function of the crop growth volume and statistical field distribution of the crop weight represented to be the normal distribution N (μ, σ²)≈N(W, s²), When fertilizing function correspond to degree of the individual crop weight was decided to be y=f(W), the total amount of fertilizer distribution per plant population n, Y was shown as follows:
Y=n∫^∞₀N(W, s²)f(W)dW
Now, f(W) was decided to be 0 at 5% range of it and g(W)=aW+b(a<0) at the rest of it. Therefore, the coefficient a, b under the condition of W=48.8gf, s=20.27gf was shown as following equation:
47.6a+0.95b=42
As the crop weight W was difficult to measure directly by non-destructive method, the crop width parralleled to the row direction L was introduced as the variable to estimate the crop weight by the result of the regression analysis. At the experiment of spring-sown chinese cabbage cultivation, the regression line equation of W=4L-70.4(r=0.88**) was obtained and four treatment plots described below were considered and accepted to fertilize crops correspond to the crop growth
A: even fertilizer plot (y=42gf)
B: variant fertilizer plots (21.5cm≤L≤38cm)
I-g(L)=-0.8L+68.3(a=-0.2, b=54.24)
II-g(L)=-1.6L+92.4(a=-0.4, b=64.26)
III-g(L)=-2.4L+116.5(a=-0.6, b=74.27)
In case of giving the lighter crop much fertilizer and the heavier crop less fertilizer, the more difference among the applied amount of fertilizer distribution there was, the less difference among the yield (total crop weight and eatable weight) there was. The uniform product would be able to be resulted by the alternative fertilizer treatment.
The theoretical fertilizing function to minimize the difference among the crop yield was finally obtained as g(L)=-3.6L+152.7, however, which should be confirmed by the actual cultivation experiment.

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The research study was intended to investigate farmers actual exposure to pesticide following cucumber cultivation in greenhouse. The aerial concentration of TPN (75% wettable powder) and DM TP (40% emulsifiable concentrate) sprayed by power sprayer and the dermal exposure amount to both pesticides were measured. The cycle of pesticide use, the spraying frequency of a given pesticide, and the working hours in greenhouse were also investigated. It summarizes as follows;
1. In general, the operator sprays pesticide moving forward along the ridge. In this case, the aerial concentration of TPN diluted 1100-fold (dilution based on the available component) was about 200μg/m³, and that of DMTP diluted 2500-fold was about 100μg/m³ around the operator. But this aerial concentration could be decreased by the spray of backward movement and the improvement of spray condition.
After spraying, about 2μg/m³ of TPN and about 6μg/m³ of DMTP were detected in greenhouse for a week.
2. In the case of spray of forward movement, the dermal exposure amount to TPN (1100-fold dilution) was approximately 0.01μg/cm²·min at face, and 0.1μg/cm²·min at hand. And that to DMTP (2500-fold dilution) was approximately 0.007μg/cm²·min at face, and 0.05μg/cm²·min at hand. These dermal exposure amount could be also decreased by improving the spray condition.
3. Pesticide was sprayed about three times a month. Therefore it turned out that the farmers are exposed to pesticide once every ten days.
A farmer used about ten kinds of pesticide in a year, and the spraying frequency of fungicides was consider-ably higher than that of insecticides.
The working hours in greenhouse was 30 to 40 hours per person per ten ares in ten days. In these working hours farmers are exposed to pesticide residues.

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