For this work thinning was performed by a tractor mounted John Deere

synchronous electronic thinner which included an electric energy source, a

sensing probe and a hydraulically activated thinning knife (Figure 1). Contact

of the metallic probe with a plant completes an electric circuit which activates

a solenoid valve, directing hydraulic oil to the knife actuator. The knife is

positioned ahead of the probe to prevent removal of the plant being sensed. The

length of the knife determines the remaining space between plants, A delaying

action mechanism in the electric circuit prevents the knife from swinging again

until sufficient time has elapsed for the activation of the probe by the next

plant. It is a sophisticated machine which requires careful adjustment and opera-

tion to perform satisfactorily.

Experiment 1

 In the first field germination test lobelle gave 86% germination and EES

279 76%. Vigor and uniformity were slightly superior for lobelle one week after

planting. Vigor one month after planting was equally good for both lobelle and

279. Conditions for growth were excellent during the test.

 The data accumulated represent the mean of four replications of 30-foot

plots. The desired distance between plants was 8 inches or 45 plants per 30-foot

plot. In the first test, summarized in Table 1, thinning of the EES 279 plants

was performed with three different plant sizes. Plants 10 inches tall were

difficult to thin since the large leaves maintained prolonged contact with the

probe resulting in a continuous activation of the cutting knife. With 6-inch

tall plants thinning was appreciably improved, although the number of doubles

(plants closer than 2 inches) was high. With 2-inch tall plants, thinning was

slightly more effective than with the 6-inch plants, but the number of doubles

was still high because plants smaller than 2 inches failed to touch the sensing

probe. Failure to obtain 45 plants per 30-foot plot was partly because the

8-inch cutting knife was too long.