[page 113↓]

6.  Conclusions

The bending resistance of the cereal stems is highly related to the mass of the stems, thus enabling the biomass sensor pendulum-meter to utilise this fact as a contact measurement to sense non-destructively site-specific cereal crop biomass. The sensor provides the opportunity to measure on-line as well as on-the-go the heterogeneity of the crop biomass, and there is good evidence that the obtained data can be used as a decision base for a site-specific on-line real-time application of plant growth-regulators and fungicides.

This work gives a proper understanding of the manner in which the pendulum-meter operates with regard to the cereal plants, although calibration is advisable before measuring. Several factors have shown an influence on the sensory measurements, such as wind, weeds, rapid crop growth and differences in plant development within the field, stem and root fungi diseases, depth of tramline, variety, year and season, plant height, and stem inclination. In the here presented work it was only possible to identify these factors, but the magnitude of their influence of the measurements remain unexplored. Determination of this magnitude will have to be done in future test trials.

As the operation period is concerned, it has to be said that the pendulum-meter can not be used for the earlier applications in plant protection, neither for the early spraying of plant growth-regulator, nor for the early fungicide application. For these growth-stages, other sensors such as a NIR sensor or a “green” leaf reflectance sensor have to be developed and utilised as a decision base for site-specific applications of plant growth-regulators and fungicides.

Unfortunately, relatively little attention has been devoted to biomass, in terms of fresh mass or dry mass, as a decision base for site-specific matters, due to the usually destructive and time-consuming sampling. It therefore constitutes an unexplored parameter regarding the site-specific or general relationships between biomass and various characters, such as fungi development, lodging, soil fertility, crop density, and plant height. The here presented field trials clearly show that the measurements of the pendulum-meter can be used as a decision base for the site-specific application of growth-regulators and fungicides, although the relationship between lodging and biomass, and between most fungi and biomass needs further examination. Furthermore, the question arises about the proper amount of growth-regulators and fungicides whether they are sprayed according to biomass, according to leaf area index, or based on another method. With regard to plant growth-regulators, there appears to be a reasonably clear dependency of lodging on bending resistance of the cereal stem. As the results of this work indicate is the main cause for the deviation of the pendulum also the bending resistance. Consequently can be assumed that the [page 114↓]pendulum-meter is well suited for a site-specific application of plant growth-regulators. Although lodging constitutes a phenomenon impossible to forecast and difficult to manage due to the complicated nature of lodging and the problems to assign cause and effect relationships. It can be assumed that the work of HITAKA 1968 provides the best basis for either calculating site-specific necessary amounts of a plant growth-regulator for a given weather situation or to test for a specific plant character HITAKA 1968 associated with lodging. Furthermore, research should be conducted on the biomass-lodging relationship, as well as the biomass-plant height relationship.

In difference to the site-specific application of plant growth-regulators is the site-specific fungicide spraying not related to a factor associated with the measurement principle. The here used approach for site-specific fungicide applications is based on two generalisations, of which the first is a close relation between biomass and leaf area as the prime spraying object. The second is that the fresh mass itself is the prime spraying object for systemic fungicides, assuming that the fungicide needs a specific level in the plant for successfully defeating the fungi disease, as it is successfully used in human medicine for a long time with regard to for example vaccination. Both approaches face the problem of calculating the proper amount of fungicide agent for successfully defeating the disease, bearing in mind that most fungi developments are dependent on weather conditions and a reduced application rates is always an increase in risk. To successfully manage the increased risk a co-operation with decision support systems, such as PRO_PLANT, crop models and weather forecasts would help implementing a sensor system for a site-specific fungicide application, whatever sensor that would be. As with site-specific applications of plant growth-regulators faces the pendulum-meter based site-specific fungicide spraying the problem that the pendulum-meter is not operating at early fungicide applications, hence other sensors have to be developed for that purpose.

It follows from an on-line sensor that the field sprayers can spray on-line and in real-time the wanted amount of spraying agent. A direct consequence is a change in the data processing for the field sprayer and technical modifications of the field sprayer to rapidly alternate application rates.

Further research areas are site-specific fertilization according to biomass data, yield mapping of whole plant silage, biomass mapping for determining N-losses and N-return. With regard to pastures and grasslands the pendulum-meter can replace the disc-meters and plate-meters for sensing grass yield, arranging of management zones in pastures according to pasture yield, and site-specific fertilization of pastures and grasslands.

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