Effect of white clover and perennial ryegrass genotype on yield and forage quality of grass-clover and grass-clover-forb mixtures

Grass-clover mixtures have shown a higher yield, higher yield stability and higher nutritive value compared to individual species in monoculture. The number and identity of species in a mixture are important factors for the mixture’s productivity. Species complementarity is assumed to be a key mechanism determining the mixture performance. Not only species but also genotypes might have different complementarity to their mixture partners so that the genotypes’ performance might be different in monocultures and mixtures. Moreover, resource availability can be expected to affect the species complementarity. To study how and to which extent the genotype affects yield, yield stability and forage nutritive value in different mixtures, two different studies were carried out in two experimental stations of Georg-August-University Göttingen, Germany. In the first experiment, we studied the effect of perennial ryegrass (Lolium perenne L.) genotypes on mixture yield and yield stability. We hypothesized that the performance of perennial ryegrass genotypes in terms of yield and yield stability would differ between monocultures and mixtures. We also assumed that the effect of the perennial ryegrass genotype on accumulated total and species-specific component yield over four years would be decreased with increasing number of partner species. Four genotypes of perennial ryegrass differing in two traits (growth form: prostrate or upright, phenology: early or late heading) were grown (i) in monoculture, (ii) in binary mixture with white clover (Trifolium repens) and (iii) in four-species mixture with white clover and two forb species (ribwort plantain, Plantago lanceolata and dandelion, Taraxacum officinale). Our results showed that the treatments with the upright growth form of perennial ryegrass were higher yielding than the treatments with the prostrate form, but this effect decreased from monoculture to four-species mixtures. Phenology did not have any effect on accumulated yields over four years. The perennial ryegrass genotype significantly affected the mixture components’ yield. Between- and within-year yield stability was generally highest in the four-species mixtures and lowest in the monocultures. To test the effect of the white clover genotype and resource availability on mixture performance, we established an experiment as a part of the IMPAC3 project in two sites which were noticeably different in terms of soil depth, texture, and precipitation. We hypothesized that white clover genotypes would perform differently in terms of productivity, yield stability and forage nutritive value in monocultures and mixtures. We also assumed that a lower level of resource availability might increase white clover competitiveness and affect mixtures’ performance. Eight genotypes of white clover, one variety of perennial ryegrass and one variety of chicory (Cichorium intybus L.) were sown as (i) monoculture, (ii) binary mixture of white clover with perennial ryegrass, (iii) binary mixture of white clover with chicory, (iv) binary mixture of perennial ryegrass and chicory and (v) three-species mixture of white clover with perennial ryegrass and chicory. The white clover genotypes differed in flowering time, leaf size and yield potential. Above ground herbage was cut twice in the establishing year and four times in each of the two following years. Subsamples were scanned with a near infrared spectrophotometer to determine crude protein (CP), acid detergent fiber (ADF) and water-soluble carbohydrate (WSC). Our results revealed that the white clover genotype did not affect the mixtures’ productivity; the white clover genotype that performed well in the monoculture also did so in mixtures. One of the three mixtures at each site showed significant transgressive overyielding compared to the most productive unfertilized corresponding. Generally, the binary mixture of white clover and chicory yielded notably higher than the other mixtures and monocultures. This shows that the benefits of mixtures are more related to the species identity than to the number of species in the mixture. Site conditions also strongly affected the mixture performance: All mixtures at the fertile site yielded higher than the same mixture at the marginal site. The white clover genotype significantly affected the forage nutritive. This effect was most visible in white clover monocultures. In mixtures, it was less pronounced, but remained significant. Nevertheless, the forage nutritive value of mixtures was more determined by the partner species than by white clover genotype. White clover monocultures had significantly higher concentrations of CP and lower concentrations of ADF than the mixtures. Mixtures including chicory had a higher concentration of ADF than the binary mixtures of white clover and ryegrass and white clover monocultures. Presence of ryegrass in mixtures led to a high concentration of WSC. In a synopsis of these two experiments, the effect of plant species genotype was surprisingly small. The white clover genotype that performed well in monoculture also did so in mixtures. Perennial ryegrass genotypes affected yield stability rather than annual herbage yield. On the other hand, the inclusion of forbs into the grass-clover mixture improved yield in both experiments