IIn the context of the Vlaio-LA project “Grassland Optimization by Decision Support Tool (GrasSat)”, grass height measurements were carried out in 2022 on 15 plots across the western and eastern regions by Inagro and Hooibeekhoeve, respectively. Fresh grass samples were taken.
Dry summers cause a significant lack of precipitation
The lack of precipitation increased in the western region in different locations. Precipitation averaged 649 mm from January to October, according to Pacific Islands Institute figures from 1991 to 2020, and in the same period it fell only 398 mm in 2022. And in the region Eastern Province, 539 mm of rain was recorded. January to October 2022, while the average for that period is 654 mm. Therefore, the decrease in precipitation was directly reflected in lower weed growth and thus lower weed yield.
Mowing stopped due to summer drought
Western Region In the western region, 8 plots were monitored and pure grassland plots and alfalfa grass plots could be distinguished. The first cuttings were mowed on almost all plots of West Flanders at about the same time, that is, at the end of April. A plot of land was mowed in early May.
The dry matter yield based on height measurements averaged 3.2 t DM per hectare for this first mowing. Six weeks later, a second cut followed with an estimated average yield of DM 2.2 tons per hectare. Three weeks later, a third cut was made on two plots (B1 and B2). For the majority of other plots, the third cut was cut one month after the second. The estimated yield for this third cutting was DM 1.4 tons per hectare. At that time, the monthly mowing rhythm was fine. At the end of July, a fourth cut of B1 and B2 plots followed (average yield 1 ton dm/ha), because the grass quickly became too boggy.
A drought during the summer months threw a wrench into the works, and the monthly mowing could no longer be sustained. Growth is stunted, but due to the good recovery ability of the grassland after drought, the final cut (in fall) can be mowed in early or mid-October. This produced an average of DM 1.6 tons per hectare and was of great importance in enhancing the forage position on the various farms.
Eastern Region In Antwerp Kempen (Eastern District) we also walked through the fields with a grass altimeter every week. There we were able to distinguish between irrigated and unirrigated plots (Fig. 1). On lands that were not irrigated, a total of 5 plots were mowed. The first cut was on April 20, and further cuts followed monthly with mowing stopping in the dry summer month of August. After the last cut on October 6, growth is no longer monitored, but a small cut is usually made in mid-November.
It is remarkable that in plots in the eastern region the highest yield was achieved with the second cut, with an average of 3.5 tonnes DS per hectare, while the highest production was achieved in West Flanders with the first cut. At the time of the first cut, the total temperature in West Flanders (840 °C) was higher than in Antwerp-Kempen (704 °C), which could be a possible explanation for this. Of course, the mowing time 10 days earlier in the first cut on April 20th (East) versus the end of April (West) would also have played a major role.
Alfalfa and watering ensure higher yields
Irrigation was applied during the growing season to plots F1, F2, G1 and G2 (Fig. 1) in the eastern region, and for the latter (G) this started in mid-May. Plots F1 and F2 consist of alfalfa grass with fescue and timothy grass, while plots G1 and G2 contain alfalfa grass with perennial ryegrass. Tall fescue is known for its drought tolerance due to its deeper root system, which is very welcome in dry years.
Due to the soil type, moisture condition is higher in F1 and F2 plots, irrigation also started earlier in these lands. These factors and deep-rooted weed species may explain the higher yields on farm F plots. The third plot in particular had significantly higher yields than the unirrigated plots. However, the high frequency of mowing and the intense fertilization, together with the irrigation, ensured that the grass would continue to grow continuously and that re-growth would never be delayed. If we add the November cutoff, we can estimate the total yield at 13.8 kg DS/ha.
On farm G (with plots G1 and G2) summer stable feeding takes place. Because of frequent cuts, it was not always possible to determine the height of the grass just before mowing. The goal on this farm is not to get the highest yields from the plots, but to keep the grass growing and to ensure a constant, high quality supply of fresh grass for the animals. Irrigation obviously has an effect on maintaining the growth of weeds, for example, a large amount of fresh grass can be removed from the field in these lands even during the dry period, until very late autumn (early December).
Remarkably, in both farms, the young alfalfa grass sown with grass (F2, G1) has a lower yield in the first cut, but this reverses after the second cut in favor of the often deeply rooted young alfalfa grass.
Grass growth resumes and continues long after a dry summer
In terms of grass growing daily, we expect the same trajectory every year under good growing conditions. In the spring expect a steady increase in grass growth with its peak in late May – early June. In the summer period, there is a decrease in weed growth, followed by a slight increase again, until the growth of grass stagnates in autumn. In addition to the season, the length of the grass is also important. Higher scales accelerate regrowth on the one hand. On the other hand, with taller grass, there is also more leaf surface and therefore a higher capacity for photosynthesis. This will ensure a higher growth rate. However, over time, growth will slow as more of the old leaves die off.
Western Region In April we see good grass growth numbers in the western region. The higher temperature after winter and sufficient soil moisture triggered the first growth spurt. After mowing the first stake, we see a decrease in growth. The first signs of drought are now clearly visible, but mowing the lawn and thus shortening the grass is certainly a cause of reduced growth. Once moisture was again available, period grass growth resumed at the end of May/June, although the peak is usually much higher. At the end of June, grass growth decreased again and decreased to less than 20 kg DS/day. During the dry and warm summers, grass growth was kept at a low level. The grass was dry in many places. After much needed rain at the beginning of September, weed growth picked up again and figures of up to a maximum of 50 kg per hectare per day were recorded.
Eastern Region Good numbers of grass growth were also recorded in the eastern region in April and May, with growth of up to 160 kg per hectare per day. After the growth peak, less growth was measured at about 60 kg dry matter per hectare per day from June. However, since the end of July, a significant difference can be seen between the irrigated and unirrigated plots. The unirrigated plots showed growth of less than 20 kg DM/day until mid-September. Sometimes negative growth or consequently a decrease in biomass is observed. On irrigated plots, a gentle growth of 10 to 80 kg DM per hectare per day can be observed. After the necessary precipitation, the grass grew again on the plots without irrigation.
Disappointing VEM value during a dry summer
Samples were also taken from different plots to determine the nutritional value of fresh grass (Fig. 2). During the season, the crude protein content is usually around 220 g/kg DM, only in August the crude protein decreased to just below 200 g/kg DM. In the eastern region, the average crude protein content of 230 g/kg during the season was higher than in the western region, with an average of 200 g/kg DM. Crude fiber fluctuated around 200 g/kg DM during the season. Only in spring and autumn, when young grass was present on the plots, could a lower average content be observed.
As expected, sugar content got off to a high start in the spring. Sunny days and cool nights cause sugar to build up in the grass. As the season progressed, we saw a decrease in the sugar content. While a lower protein content was observed in the western region than in the east, we see the opposite for sugar content. The average sugar content over the year was higher in the western region than in the eastern region. This also demonstrates the well-known antagonism between sugar and protein again. Remarkably, the sugar content increased sharply again in October as a result of the sunny weather. Fall grass usually contains less sugar. With the decrease in grass growth in summer, the VEM value of fresh grass also decreased below 900 VEM per kg DS. Along with the increase in sugar content, the VEM content also increased again in the fall. So the nutritional value of fresh grass in the fall was similar to that of the spring, which is exceptional.
Fall cutting is also important
After a dry summer, roughage stocks were below average on many farms. Thanks to the much-needed rain since mid-August, the lawn has recovered well in most locations. However, on one of the plots pursued, the damage caused was too great and an overrun began. Thanks to the fall cut mowed in October and on some plots cut last fall in November, the coarse stock can still be supplemented substantially.
The measurements were achieved thanks to financial support from the Flemish government in the Vlaio-LA GrasSat project (Improving Grassland Utilization by Decision Support Tool), implemented by Inagro, Hooibeekhoeve, ILVO and VITO.