The effect of various fertiliser treatments on the yield of maize hybrids was studied on the basis of 26 years of data obtained in a long-term bifactorial split-plot experiment set up in 1967. The seven treatments (NPK ratio 2:1:1) applied were as follows (rates per hectare): 1. Control (no fertiliser), 2. 100 kg NPK, 3. 200 kg NPK, 4. 300 kg NPK, 5. 400 kg NPK, 6. 600 kg NPK, 7. 800 kg NPK. The maize was grown with the conventional cultivation techniques in continuous cropping. The results of analyses carried out with three different methods (analysis of variance, cumulative yield analysis and regression analysis) all indicated that under the given conditions the yield of maize hybrids was highest at an NPK fertiliser rate of 200-400 kg ha
. The effect of fertilisation on the maize yield was significant in 21 of the 26 years. Combined analysis of variance for the years showed that the year effect (quantity of rainfall) had the greatest effect on the maize yield, but although the year effect had a fundamental effect on the yield level it did not influence the fertiliser response pattern. The fertiliser responses of the maize hybrids were described by fitting four types of functions (quadratic, square root, inverse exponential, linear-plateau) to the yield data. It was found that when selecting the best function a consideration of the regression deviations (measured yield - calculated yield) was just as important as the coefficient of determination (R
). In 12 of the 26 years the fitting of the quadratic function was not significant and overestimated the fertilisation optimum. The fertiliser response curve generally has a broad maximum which is far better described by the square root function than by the quadratic. If the fertiliser response pattern includes a depressive phase, a square root function should definitely be used in place of the quadratic function. If the maximum of the response surface forms a plateau (as opposed to a maximum point) a linear-plateau function or an inverse exponential function can be recommended. In the present work the linear-plateau function gave the best results.
The effect of sowing date, N fertiliser rate, plant density and genotype
on the yield stability of maize was analysed using 15-year data from a
5×4×5-factorial sowing date experiment, 35-year data from a two-factorial N
fertilisation experiment and 25-year data from a two-factorial plant density
experiment. Stability analysis on the experimental treatments was carried out
using the variance and regression methods. Among the variance parameters, the
ecovalence (W), the stability variance (σ²) and the yield stability
(YS) were calculated. Based on the data of the sowing date experiment the
optimum sowing date (Apr. 24) or sowing ten days later (May 5) were found to be
the most stable due to the low, non-significant values of the variance
parameters and the values close to unity for the regression coefficients (b).
Although early sowing (Apr. 14) led to a significantly higher yield than late
sowing, the yield stability was poorer for early sowing. In the long-term N
fertilisation experiment the variance parameters indicated the least yield
fluctuation at N rates of 80 and 160 kg ha-1, though the yield
stability (YS) parameter for the 240 kg ha-1 N rate was also above-average.
Regression analysis showed that the yield level and yield stability were the
same in all environments for the 160 and 240 kg ha-1 N rates. The
stability of the 80 kg ha-1 N rate was similar, but the yield level
was approx. 1.3 t ha-1 lower. The yield stability of the plant
density response of the maize hybrids was different in each maturity group (FAO
number). The stable plant density range was broadest (50-90 thousand plants ha-1)
in the FAO 200-299 group. As the vegetation period lengthened the stable plant
density range narrowed and shifted towards lower plant densities (for the FAO
400-499 and FAO 500-599 maturity groups: 50-70 thousand plants ha-1).
The variance and regression parameters of stability analysis both contributed
to the characterisation of the stability of the genotypes and cropping systems
investigated. It can be concluded from the results that high yields and yield
stability are not necessarily mutually exclusive.