The value of nutrients in growing pastureWritten by:
Ross Kuchel
For plants to grow (i.e. photosynthesize) they need the three essential elements of light, carbon dioxide and water.As long as light, CO2 and water are not limited, the rate of plant growth is governed by soil nutrients, and this is something that we as managers have control over, i.e., if a soil is deficient in one or more essential nutrients, we can address this by applying a fertiliser that contains those particular nutrients.
To monitor the impact of nutrients on pasture growth, soil acidity and carbon, a Nutrient Subtractive Trial was established by LLS on several sites In the Braidwood/Bungendore district in September 2021, with funding from the Australian Government's National Landcare Project 2.
The basis of these sites is to demonstrate Lleblg's Law-that growth is limited by the nutrient that is in shortest supply. For example, if you address the deficiency of the most limiting nutrient, pasture growth will only increase to the point where the next nutrient become the limiting factor, and so on.
The trial sites consist of seven replicated plots. One plot receives all the main macronutrients and micronutrients required for pasture growth, four plots receive all but one, there is a control plot with nothing added (control), and a final plot with all nutrients plus lime (to alter soil pH). The nutrients tested are Phosphorous (P), Potassium (K), Magnesium (Mg), micronutrients (B, Mb, Cu, Zn), and lime (CaCO3).
Running alongside the trial is a second set of plots looking at the pasture growth response relative to varying rates of superphosphate (9%P, 11%S). TTie rates tested in kg/ha equivalent are 0 (control), 125,250,400, and 600.
Each month, the herbage mass (pasture growth) of each plot is measured and recorded. The results from September this year of the Bungendore site are shown in the table below. Table 1. Pasture growth (Herbage Mass) for September 2022, Bungendore NST site The data collected from the trial sites to date highlights phosphorous as having the biggest Impact on pasture growth.
For September at the Bungendore site, the plot with all nutrients added averaged 54kg DM/ha//day. This is compared to the control
plot (no added nutrients or lime) at just 18kgDM/ha/day (67% less), and the -P plot at 32kgDM/ha/day (-40%).
Pasture growth readings will continue to be taken throughout spring. At the end of spring, soil tests will be taken to determine levels of nutrients, soil pH and soil carbon. Economic analysis will also be done to look at the cost benefit of adding nutrients relative to productivity gains from the additional pasture grown.
If you would like to know more about this project, or have questions regarding soil nutrition and pasture production, please contact Ross Kuchel at the Braidwood LLS office on 0428 314 588 or email ross.kuchel@lls.nsw.gov.au
Article Attrition: Bungendore Weekly, Ross Kuchel#FarmingAgricultureLandManagement