Maize grain and silage yield and yield stability in a long-term cropping system experiment in Northern Italy

Abstract This study assesses maize yield and yield stability over a 26-year period in several cropping systems that are part of a long-term crop rotation and agronomic input experiment established in 1985 in Lodi, Lowland of Lombardy, Po Valley, Northern Italy. This experiment compares five fodder crop rotations, specifically: (i) an annually repeated double crop (R1) of autumn-sown Italian ryegrass + spring-sown maize, both used for silage; (ii) a three-year rotation (R3): grain maize (first year) – autumn-sown barley ( Hordeum vulgare L.) + spring-sown maize, both for silage (second year) – Italian ryegrass + maize, both for silage (third year); (iii) a six-year rotation (R6): Italian ryegrass + silage maize, both for silage (years 1, 2 and 3 of rotation) – a mixed meadow of white clover ( Trifolium repens L.) and tall fescue ( Festuca arundinacea Schreb) for hay making (years 4, 5 and 6 of rotation); (iv) a continuous grain maize (CM); and (v) a permanent meadow, established at the beginning of the experiment. All phases of the rotations were carried out every year. Each crop rotation received two levels of agronomic inputs consisting in synthetic and manure fertilization and herbicide rate, corresponding to high (A) and low (B). Treatment A represented a snapshot of agronomic inputs (synthetic fertilizers N–P–K, manure and herbicide amounts) normally applied by the farmers in the region in 1985, when the experiment was undertaken, while treatment B consisted in a 30% reduction of synthetic and manure fertilizers and a 25% reduction of herbicide rate compared to treatment A. The primary objective of this study was to evaluate the long-term effects of crop rotations and the reduction of inputs on maize yield and yield variability. The following conclusions can be drawn: firstly, over 26 years, the yield of grain maize in rotation increased steadily whilst the yield of continuous maize decreased slightly; secondly, a 30% reduction of agronomic inputs decreased the average yield less than proportionally for both grain and silage maize; thirdly, within a given crop rotation, grain and silage maize yields are more stable with higher inputs; and finally, yield stability of grain and silage maize increases with longer rotations. Therefore, management options oriented at increasing cropping system biodiversity have important implications on reducing the temporal variability on maize yield.