Maize is one of the widely cultivated crops in the world, with great importance, both in industrial and developing countries. Because of this, continuous and considerable research work is directed not only towards improving its production potentials, but also to know the interaction of its production with the environment and effects (Eder & Widenbauer 2003). Current enviromental concerns justify renewed evaluation of crop management strategies that offer promise for maintaining or increasing productivity while reducing negative environmental impacts, through integrated agriculture (Lütke Entrup et al. 1996, 1998). Genetic constituents and environmental factors affect the production of maize, as in all other cultivated crops. Climatic conditions play a vital role in the growth and development of maize, affecting the length of the vegetation periods, thereby the type of maturity group to be grown in a given zone (Schuppenies & Watzke 1985). In so-called favourable conditions, maize gets the necessary climatic requirements such as relatively high temperature (optimum) and precipitation for a rapid growth, good maturity with high yield (Hein 2002). However, in marginal climatic conditions, one or more of the climatic requirements are often not met. Marginal conditions, such as late freezing into the year, which does not only interfere with date of sowing, but also minimum soil temperature required for seed germination may not be attained in time early freezing in autumn, that increases the risk of normal maturity and harvest, especially of varieties with longer vegetation period like the stay-green type and reduced sun-shine hours during the vegetation period due to bad weather conditions are to be taken into consideration. Unfavourable environmental conditions at flowering in maize can cause cessation of ear development and ear abortion (Tollenaar 1977, Jacobs & Pearson 1991).
In cooler regions of Central and West Europe, the use of maize as a forage crop has drastically increased in the last three decades (Moreno-Gonzalez et al. 2000). The total area under maize cultivation in Germany has seen a slight increase in 2003, after a downward slope since 1997. There was a more than 6.4 % increase in silage maize grown in 2004 than in the previous year (Statistisches Jahrbuch 2004). Comparing to other European Union states engaged in maize production, 29 % of the overall cultivated area in Germany was under silage maize cultivation, only second to France with 41 % (from 1998-2003). Selection of genotypes (varieties) that would suit particular conditions of a location is a continious process, not only in maize but also in overall crop production. In the northeast plain of Germany for instance, water deficit during the vegetation period of maize is a common phenomenon which affects both dry matter yield and forage quality of corn. Generally, the accumulation of biomass by crops results from the amount of incident photosynthetically active radiation (PAR) intercepted by the canopy and from the efficiency with which the intercepted PAR is converted into dry matter. Dry matter accumulation is closely associated with leaf area development. The development of leaf area in turn is a function of both leaf size and leaf numbers. These factors may change differently depending on the genetic material (varieties) involved and the environment in which the plants are grown. The expansion and duration of green leaf area determines the fraction of incident radiation intercepted by the crop (Andrade et al. 2000, Otegui & Andrade 2000).
In Germany only varieties, which have successfully undergone a two years Bundessortenamt test and have been in the variety list or were released from other European Union countries are grown (Bundessortenamt 2003). In the variety list of 1999 for example were 51 early, 80 mid-early and 14 mid-late varieties totalling 145. More than 226 varieties are in the general EU variety catalogue and therefore may be used. These varieties are again released to regional variety trial research stations (LSV), whereby they are tested for three years before they are finally released for cultivation (in the market). The results from regional variety tests serve as a basis for recommendation of silage maize grown in specified locations. In this experiment some of the earlier recommended silage maize varieties (early and mid-early) for Brandenburg region were used (Köhn 2002).
Information on LAI of forage maize varieties are important in order to characterize the maturity condition of residual parts of the plant (stems and leaves). Many methods exists to measure LAI during vegetation period (Hammer et al. 1998, ŠestÁk et al. 1971). The aim of this experiment was to use the leaf parameters (LAI, LA) of the various forage maize maturity groups measured by two methods, manual and LAI 2002, to present the variability in the development of leaf area of the different maturity groups during the vegetation period and between the years. Knowledge of the maturity condition of the leaves and loss of assimilation area during the vegetation period between the years and especially in a location with limited water availability like location Berge will help to characterize the suitability of certain varieties for such a location. The regional prognosis model (Rath et al. 2002) helps to estimate the optimum harvest time for silage maize. However, uncertainity in estimating the maturity time due to uncertainity in the changing weather conditions like drought stress and heat do exist. Additional criteria on leaf status at silking and post anthesis that may influence dry matter yield and dry matter content under conditions of drought stress, thereby affecting harvest time, can be the additional information on the prognosis for optimum harvest time of silage maize. The experiments also seek to answer such questions like:
How do maize varieties of early and mid-early maturity groups differ in LAI and leaf area development?
What differences exist between the two methods used to measure LAI (manual and LAI 2000)?
What are the differences in SLA between the maturity groups and year?
Does stay-green have advantage over non-stay green?
What influence has LA of silage maize on yield and forage quality parameters?
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