In order to evaluate plant production in various systems, a full evaluation is necessary such as the economic method, which comprises work and cost input (SOBCZAK 1982]. HARASIM (1989, 1991) defined the criteria for the above method. Some of the authors described the wide applications of the economic method implemented and enhanced by energy requirement analysis for the evaluation and balancing of input in different types of crop rotation as one of the criteria of their evaluation [KUŚ et al. 1988, RZESZUTEK and SOBCZAK 1992, STUPNICKA-RODZYNKIEWICZ and LEPIARCZYK 1991, WIELICKI 1990b, ZAWIŚLAK, RZESZUTEK and RZESZUTEK 1992, FEDEJKO et al. 1994].
NAWROCKI (1984) put forward the opinion that in order to rationally use energy in one has to find the proper production directions and specializations in the given soil conditions along with the local agricultural food industry infrastructure. RYSZKOWSKI (1988) predicted the changes in production conditions resulting from the of limitation of ecological hazards and stated that an improvement in the economy in agricultural areas to intensify production and increase work efficiency is necessary. The above change to a wide extent depends on an increase of the energy delivery to rural markets and increase in the knowledge and educational levels of agriculture.
Returning to the beginning of research into plant-production energy, it is worth mentioning that this field in Europe was developed by PIMENTEL (1974) and LEACH (1974). In Poland, this subject was taken up by workers of IBMER and SGGW: WÓJCICKI (1981), MACIEJKO (1984), ZAREMBA (1986), ANUSEZEWSKI (1987), NOWACKI (1988), in Poznan WIELCKI (1987) and in Olsztyn SOBCZAK (1982) and ORLIŃSKI (1986). In the former Czechoslovakia the field was researched by KREJČĺŘ (1986, 1988), STRATŠIL (1990), ŠIMON (1990), STRAŠIL and ŠIMON (1988).
The method of energy evaluation of plant cultivation in crop rotation and monoculture systems is not free of difficulties and is inexact. Energy provided by a farmer to a certain plant depends on its position in crop rotation compared to a field fertilized by manure. The method of manure-evaluation is very difficult [FLUCK 1991, NOWACKI 1988, ZITTA 1992]. Two strains of plants are distinguished. Directly and indirectly fertilized by manure. In case of manure application for heavy soil at the rate of once every four years, there should be certain proportions in each subsequent year: 40, 30, 20 and 10 percent. If manure is used once every three years like which is used for light soil, the proportions are as follows: 60, 30 and 10 percent. This is a simplified application of manure usage. The quality and degree of its application depends upon many factors such as the method of animal feeding, manure storage, the kind of soil, the depth of implementation, weather conditions, the species of cultivated plants and crop rotation [ KREJČĺŘ 1986, NOWACKI 1988, ZITTA 1992]. There are also different methods of energy-amount description, which are provided by manure. The above method may be equivalent to calculating the amount of nutrients in manure or measuring the combustion energy of the manure. KREJČĺŘ (1986) used 4,25 GJ as an energy equivalent per one ton of manure while STRATŠIL (1990) used 9,25 GJ.
The description of after-harvest left-overs provided in the whole rotation appears to be similarly difficult due to work-consuming analysis. Some authors use estimated data from accessible references [KREJČĺŘ 1986, NOWACKI 1988].
It is very difficult to describe the amount of energy provided by an individual [WÓJCICKI 1981, KREJČĺŘ 1986, GOLEMO and MICHAŁEK 1988]. This type of energy in agriculture is differentiated by weather conditions, technology of plant cultivation and the choice of equivalent indicators describing the amounts of input of operations such as technological operations. WIELICKI used equivalent indicator 1,3 MJ/Mh, FLUCK (198 1) 75 MJ/Mh but KREJČĺŘ ( 1988) and ZITTA ( 1992) used 40 MJ/Mh as do most of the Polish authors [FEDEJKO et al. 1994, RZESZUTEK and SOBCZAK 1992, ZAWIŚLAK, RZESZUTEK and RZESZUTEK 1992). Apart from that, the value of labour is very different. Beginning from simple physical work up to specialized labour necessary to service complex electronic equipment and up to management level, which not only requires individual attributes, but also education and experience equivalent to the scale of the tasks.
According to WÓJCICKI (1981) the work- input should be calculated in such a way as to be equivalent to objective indicators of physical labodr substituted by mechanical work. More attention to individual labour input analysis was paid by FLUCK (1981), GOLEMO and MICHAŁEK (1988), WIELICKI (1988). The multi-method approach to labour force evaluation makes one consider whether human labour should be included in energy calculation or not. In Poland, where agriculture has a low state of technology and physical labour is implemented widely, the omission of it in calculation would be misleading [WÓJCICKI 1981].