There has been much descriptive work carried on plant root systems in the past, but quantitative studies have lagged behind equivalent work on plant tops, probably because of the practical difficulties of measuring root lengths. Root length has normally been measured by excavating soil and washing out roots, and then using a map measuring wheel, a ruler or the Newman method on the cleaned roots or photograph of them. The measurement methods of root length are very simple, but they require a great deal of labor and a lot of time.
The technique of image analysis has come to be more widely used in recent years. The measurement of the root length is made by using an image analyzing computer. The basic principle employed here is after the Newman method. It relates root length to intersections between roots and randomly oriented straight lines according to:
R=πNA/2H
where R is an estimated root length in an area A, N is the number of intersections between roots and randomly oriented straight lines, and H is the total length of the lines.
A root photographic image which is put into a computer, is separated into the “black” roots and the “white” background. The randomly oriented straight lines are replaced by scanning lines of image analyzing computer.
The results obtained by the present experiments can be summarized as follows:
The estimated value of a sample differed with the direction of the scanning lines. This variation depends on that the Newman method holds in a strict sense only when the scanning is done in a randomly oriented manner. The inaccuracy which comes from using a computer can be improved by rotating a sample image which is taken in the computer.
The accuracy of this system is related to the distance between the scanning lines. The narrower the distance is, the closer the measured value approaches the true value.
When we adopt this measuring method using a computer or hand-operated, it is necessary that the following conditions be satisfied.
1) In the process of measuring a sample, the number of rotation times of the sample must change more than twice. However two rotation times of the sample are adequate for the accuracy of the measurement and in practical application. Therefore the length of the sample can be estimated at the average of 2 times measurements taken after rotating the sample 90°.
2) The distance between scanning lines must be less than 10mm.

View full abstract

On the Ogasawara islands, tomatoes are usually sown in late summer and seedlings are then transplanted to the fields in the fall. Early yields are very low, however, because of poor fruit-set in lower clusters. OZAWA (1986) reported that fruit-set was largely influenced by plant water status. Several experiments were carried out in the present study to discover effective ways to reduce plant water stress.
In the first experiment, the effects on fruit-set of leaf water spray were investigated. Cultivar ‘AZUMA’, sown on August 25, 1982, were transplanted to the field on October 27, 1982. Each of six plots received a different treatment: Plot A was untreated, Plot B was mist-sprayed at 9:00, Plot C was mist-sprayed at 12:00, Plot D was mist-sprayed at 15:00, Plot E was irrigated, and Plot F was irrigated and was mist-sprayed at 12:00. Mist-spraying was done continuously for nine days from October 29, during the period of first cluster anthesis. Irrigation was done intermittently for 22 days from October 27. First-cluster fruit-setting was improved in Plot F and D. Second-cluster fruit-setting increased in the following order: Plot D, Plot C, Plot B, Plot F, Plot E. Total yields of the first and second clusters were high in Plots D and F.
In the second experiment, diurnal variations in water saturation deficit (W.S.D.) were measured on November 2. In Plots C and D, W.S.D, was decreased for two hours after spraying. Irrigation also markedly decreased W.S.D. throughout the daytime. W.S.D. was lower throughout the daytime in Plot D than in Plots A, B, and C.
The first two experiments showed that fruit-setting was improved by rapidly decreasing plant water stress in the evening. Two interesting phenomena were also observed: plant water stress fell at midday after the evening decrease had continued for four days, and fruit-setting of the inflorescence that bloomed after treatment were also improved. These findings suggest that plant physiological changes can lessen plant water stress.
In the third experiment, plants were cultivated in pots of different sizes in a greenhouse. Leaf water potentials increased with increase in soil mass.
In the fourth experiment, practical measures to promote root development were examined. Early transplanting to the field and cutting of three folioles in the upper part of each leaf at the time of transplanting effectively promoted root development.
In the fifth experiment, yields from plots that had been given different treatments were compared with those from the irrigated plot. Plots were divided according to treatment into control, soil surface irrigation, sprinkler irrigation, early transplanting and early transplanting plus leaf cutting. Total yields of first and second clusters increased in the following order: early transplanting plus leaf cutting, early transplanting, soil surface irrigation and sprinkler irrigation. Early transplanting and leaf cutting at the time of transplanting appears to be more valuable than irrigation for improving fruit-setting on the Ogasawara Islands.

View full abstract

Much work has been done in the analysis of light interception by a canopy in relation to its structure. However, it is questionable if the work so far has given satisfactory answers to practical problems. For example, north-south row orientation prevails in winter tomato cultivation in Japan, presumably without any scientific reasoning and so far no analysis has been made on the row orientation effects of tomato crop.
In the present report, therefore, effects of row orientation on the direct radiation interception by tomato crop were investigated. The very complicated shape of tomato leaves makes it impossible to directly measure the canopy structure. We utilized, consequently, fisheye photography for the analysis. Two canopies were photographed three times from January to March in 1984, details of which are listed in Table 1. Figure 2 shows the camera positions within each canopy. One of the advantages of the fisheye photography analysis employed here is that the interception of direct solar radiation can be analyzed for any row orientation, time of year, time of day and the latitude, no matter how the real situations at the time of photographing are, if the sun position on the photograph can be calculated.
Every photograph was checked if the assumed direct solar radiation is intercepted by the canopy or not. The percentage of the number of photographs in which the assumed direct solar radiation is intercepted gives the ratio of the intercepted direct solar radiation to the incident direct solar radiation, which is called here canopy absorptance. With the values of the canopy absorptance, the ratio of the daily integrated intercepted direct solar radiation to the daily integrated incident direct solar radiation (daily canopy absorptance) was calculated assuming a well-known formula for the time variation of the direct solar radiation intensity. Results for the latitude of 35°N were presented in Figs. 3 and 4, in which _??_, _??_and _??_ correspond to the canopy structures photographed on different dates listed in Table 1.
In winter, canopy absorptance of east-west orientation keeps a high level through the day, whereas that of N-S orientation falls at about 10:00 drastically, resulting in a higher value of daily absorptance for E-W orientation than N-S orientation. In summer, E-W orientation has low canopy absorptance except the beginning of the day, while in N-S orientation canopy absorptance falls toward the noon almost linearly. Daily absorptance of N-S orientation falls gradually from winter to summer, whereas that of E-W orientation falls drastically between March and April.
These results give rise to a question on the above-mentioned situation that N-S orientation prevails in winter tomato cultivation in Japan.

View full abstract