Irrigated ryegrass and white clover pastures form a major part of pasture-based dairy operations in the Western and Eastern Cape provinces. Nitrogen fixation of legumes such as white clover, serves as an important component in increasing yield. However, the importance of fertilisation remains as, despite producing N for pasture grass species, only about 70% of potential herbage yield can be achieved using legumes without any N fertilisation. A possible alternative to standard fertilisation for increased N availability in pasture systems is the use of biostimulants, such as fulvic acid and bioflavonoids. Plant biostimulants are defined as stimulants that contain substances and/or microorganisms whose function, when applied to plants or the rhizosphere, is to stimulate natural processes to enhance/benefit nutrient uptake, nutrient efficiency, tolerance to abiotic stress and crop quality. Research on both fulvic acid and bioflavonoid application in common crop species showed increases in soil fertility, crop quality and crop productivity. However, research is lacking with regard to the effect both fulvic acids and bioflavonoids on pasture species. Consequently, the aim of the study cited was to determine the effect of soil application of a carbohydrate-derived fulvic acid and bioflavonoid biostimulant on herbage yield and nutritive composition of a mixed perennial ryegrass–clover pasture in winter and summer.

A pasture paddock of 3.3 ha was used for the study. It consisted of a mixture of one-year old perennial ryegrass, white clover, and red clover. A 2 × 2 factorial design, arranged as a randomised block with three blocks was adopted, viz. 12 experimental plots. Each plot was approximately 15 × 132 m in size and plots were separated by mobile electric fencing for grazing management. Two factors were studied, grazing period being the first. Winter and summer were chosen as grazing periods, and two grazing cycles per grazing period were examined. The winter grazing cycle lasted 35 days and the summer grazing 21 days. Standard fertiliser practices were followed according to best practice recommendations obtained from soil test results. No-tillage methods were employed to establish the pastures one year prior to the commencement of the trial and the pastures were irrigated, with the irrigation frequency based on estimates of evapotranspiration demand and rainfall. Lactating Jersey cows strip-grazed the plots twice a day during the grazing cycles where new pasture was available after each milking. The cows were not allowed to graze previously grazed plots before a growth period of at least one grazing cycle, and they were moved to the next block as soon as the fastest group was finished grazing their plot. According to the herbage yield and DM requirement per cow, camp sizes were adjusted before each grazing event. The cows received 4 kg of concentrate supplementation per day and an average pasture allocation of 12 kg per cow per day. Samples were separated into a ryegrass component, a clover component, and a non-sown component. The non-sown component consisted of broadleaved weeds and weedy grasses.

The contribution of the ryegrass component to total herbage yield was higher in the control treatment compared to that of the biostimulant treatment in both the winter and summer grazing period, whereas the clover and non-sown components were unaffected. The biostimulant treatment showed a tendency for a higher contribution by the non-sown component in both the winter and summer grazing periods. The non-sown component was the highest (21.05%) with the biostimulant treatment, partially explaining the reduced ryegrass component. The soil biostimulant treatment had no effect on the nutritive composition of the pasture, but the total herbage yield of the perennial ryegrass–clover pasture responded positively. Overall, herbage yield effects were more pronounced in the summer compared to the winter.

In conclusion: future studies should investigate the use of biostimulants with varying fertiliser levels to potentially reduce fertiliser inputs in pasture-based dairy production systems.