Drought in perspective

Have you ever thought of drought in the context of carbon balances? 

Graziers run a carbon business, and they are out of business, when animals consume the last of the carbon residing above ground. A producer’s day job is recycling carbon and then selling carbon based products, be it meat or fibre.

 

Who does drought visit and when?

 

Droughts are the climax of a dry spell, however the arrival of drought is determined by more than just lead up rain. The timing comes down to the ability of paddocks to generate some carbon flows from any isolated small falls of rain to postpone drought. This relies on how well soil is structured to let rain in and the ability of plants to respond. Of course, good operators sometimes postpone the drought phase for long enough to escape it with, what others call, drought-breaking rain.

Thinking cause and effect, drought is the run-down of “short term” carbon above ground, i.e. ground cover.

One strategy for slowing the onset of drought is to increase the percentage of perennials in the pasture. The advantage of perennials is that they can respond to isolated single falls of rain while annuals can’t.

The survival mechanism for perennial grasses to cope with dry times is to go into dormancy. Interestingly, soil microbes have the same strategy. During dry periods, perennial grasses will be going in and out of dormancy, adding a bit to ground cover each time they come out of dormancy.

The survival mechanism for annuals is to avoid dry times. They do this by producing seed so that the next generation can germinate and grow next time there are good conditions. This is why pastures weighted towards annuals are fair weather friends and let you down quickly when the going gets tough.

Because perennials are the only reliable source of carbon flows over time, avoiding drought is all about maintaining the health/resilience of the perennials.

Having paddocks with healthy/resilient soils is the other aspect of slowing the onset of drought. Healthy soils let rain infiltrate quicker, reducing run off. This is very important because there seems to be a pattern lately for rain to be heavier, even in dry years. Soil health relies on carbon flows to feed the soil life needed to keep it well-structured and fertile.

Plants fail first and then the soil starts to fail. This is because carbon flows reduce as plants become unhealthy. So in reverse, with better management, it is the perennials that repair quicker than the soil. Whichever way you look at it, plant management after rain determines your destiny.

 

Increasing short term carbon balances in perennials postpones drought

 

If you want perennial grasses to respond to small falls during dry periods, they have to be resilient.

Resilience relies on good energy reserves needed for coming out of dormancy and, increased root volume to allow them to source more water and nutrients. Because energy reserves and roots are short term carbon, they will disappear quickly without adequate management of carbon flows.

 

Plant roots are important for water infiltration


Plant roots act as wicks to take water down through the soil

Paddocks are more water efficient and have increased capacity to capture resources when plants are physically present.

 

Roots, which are 45% carbon, act as “wicks” to take water down through the soil profile, especially important with harder soils.

 

This is achieved by water travelling down beside roots. Better managed plants, with more extensive root systems, distribute water faster through the soil and to greater depth.

 

With perennial grasses, the roots grow and die back. This results in cavities where roots have previously been. These cavities are very effective for water infiltration.

 

This wick effect is especially important if isolated small falls of rain are heavy.

 

Water use efficiency relies on plant health & soil health

 

The example that follows demonstrates why some producers achieve higher carbon flows from isolated falls during dry periods and so postpone the arrival of drought. It relates to the combination of better soil structure and the wick effect.  

The exercise documented in the box above, was one I carried out in a degraded paddock. It was a harder soil type where both the soil and perennials were unhealthy in a lot of areas. It followed 50 mm (two inches) of rain. I used a piece of high tensile fencing wire many times to establish how far water penetrated depending on the configuration of grass cover and the health of the area being sampled. It is likely that the isolated perennial grass plants, with access to less water, went into dormancy quicker than the ones in the grass clumps. When management of carbon flows changed for the better, following this exercise, the isolated perennial grass plants acted as a catalyst to see small clumps develop, i.e. there was already a source of carbon flows unlike the bare areas.

 

Drought preparedness is just as important as forecasts 

In recent times, there has been a focus on improving long term weather forecasting. This is a step in the right direction provided graziers don’t become too focused on when to destock instead of reducing the impact of drought. Both strategies are risk management, so should be considered together and not seen as separate issues.

 

Conclusion

 

Natural droughts are a lack of rain, while man made droughts are a lack of carbon flows from what is actually enough rain to just remain in production.

 

Perennial grasses are well adapted to drought but not to continuous defoliation, because it runs down their energy reserves.

 

Those who manage carbon flows better are stressed less by dry times.

 

Make every drop of water go through a plant. Water must leave via transpiration and not runoff. 

 

The smart operators think about drought when it rains. 

 

Next week’s discussion:   “Carbon levels influence rainfall”

Alan Lauder