July 30, 2018

More pasture per drop

Rainfall and/or irrigation drives pasture production as it supplies plant available water. However, availability of water is controlled by four main pathways: transpiration, evaporation, run-off and drainage. Therefore, factors that reduce run-off and evaporation, and improve transpiration efficiency will also help to increase dry matter production and feed availability.
Diagram showing water loss in soil
Diagram showing water loss in soil

Evaporation

Evaporation from the soil is an unproductive loss. Evaporation losses can be reduced by maintaining good ground cover, which is very difficult in current drought conditions.

Transpiration

Transpiration is necessary for plant growth. As the plant takes up carbon dioxide (CO2) for photosynthesis through the respiration openings in the leaves (stomata), water is transpired and exits the plant tissue. As soon as water is in short supply, stomata close and biomass production declines because of a lack of CO2 inside the plant tissue. Transpiration is also essential to cool the crop tissue and to prevent heat stress. It triggers the uptake and flow of water in the plant, thereby the uptake and movement of nutrients.

How can balanced plant nutrition contribute to make best use of available water?

Pasture growth is directly related to transpiration. Plants use water, nutrients, CO2, and sun light energy to make energy for growth through photosynthesis. Adequate nutrition increases the efficiency of this process.

All nutrients are important to maximise dry matter production from available moisture.  The major nutrients; nitrogen, phosphorus, potassium and sulphur receive more attention as shortages of these nutrients have a greater impact on dry matter production.  This is highlighted in the photo below from Yara trials, where water use was measured for low and optimum nitrogen rates and related to grain production. This also can be related to increasing dry mater with the same quality of water.

Reduce water use by using optimum N

The major nutrient influence growth by;

  • Nitrogen is essential for chlorophyll and enzyme formation with both required to metabolise CO2 into plant biomass. Lack of nitrogen reduces photosynthesis, resulting in wasted water.
  • Adequate Phosphorus availability supports early root and shoot development, contributing to early pasture density and access to deep soil moisture.
  • Potassium is essential for controlling stomata function. In the case of deficiency, stomata don’t close appropriately and water is wasted.

Micronutrients such as Boron, Copper, Zinc and Molybdenum also play important roles.

Fertiliser applications to drive production

Yara Crop Nutrition have been working closely with agronomists and growers to improve dry matter production from improved pastures.  Our focus has been to lift production during autumn, winter and early spring, generally when production has been lower.  To achieve this, we have been focusing on 3 applications;

Autumn: The combination of nitrogen, phosphorus and sulphur supplied by an application of 125-150 kg/ha of YaraMila 21-7-3(4) has proven valuable in producing more feed during early winter. 

Winter: 65-80L/ha Yara Liquids SULSA 24-3-0+6S applied with ProGibb has produced an extra 900 kg/ha dry matter after 28 days compared to the untreated area.

Early Spring: Another application of 125-150 kg/ha of YaraMila 21-7-3(4) to promote early growth and produce feed before spring starts.  Consider YaraMila 17-5-10(4) if you are planning to cut hay or silage to supply additional potassium.