How to reduce the impact of drought on crops and soil
Drought can be a stressful experience. However, with some preparation and looking to lift farm productivity once drought-breaking rains occur, the impact of dry conditions can be minimised.
Prioritising summer crop establishment and maximising total dry matter (DM) content are important. The usual principles apply to growing healthy crops. These include understanding the total DM required by animals, using soil and herbage test results to understand the nutrients available, and thinking about how to wisely use nitrogen (N) on-farm. Ask yourself: Will the N response be limited by low soil moisture at the time of application?
A feed budget establishes the total DM requirements and how much of a feed deficit a summer crop could fill from a lack of pasture growth in dry conditions. Completing a feed budget ahead of time allows on-farm feed decisions to be made early.
As soil testing is best practice before sowing any crop, this information identifies if there is a need for capital fertiliser and provides information on the nutrients at or below optimum. This then allows for the correct amount of fertiliser to be applied.
Nitrogen application decisions are impacted by soil moisture and when rainfall is expected. If weather conditions become dry, the potential yield of the crop is influenced by the lack of moisture and thus the amount of N to be applied as a side dressing needs to be adjusted to suit conditions and the projected yield. If dry conditions are common, plan to apply N early to encourage the crop to establish before weather conditions create a stress point.
After a long dry period, a drought can be considered broken only when there has been significant rainfall, generally more than 50 mm. Recent studies¹ with N applications to pasture once drought-breaking rains have occurred, show there is some value in applying N as soon as the first drought-breaking rain has occurred.
Research also suggested that waiting until the drought is fully broken is the time to apply N. Once an application has been made, the pasture should be spelled for four to six weeks to allow plants to recover and grow in response to the N applied.
There may be an increased risk of nitrate poisoning if there has been an extended period of cool and cloudy weather after drought and N has been applied to soils that have high levels of mineral N. This risk applies to both forage crops and pasture. If there is any doubt, check for nitrates before grazing by sending a herbage test to a laboratory for nitrate testing. When done correctly, the results can be returned quickly so a swift on-farm feeding decision can be made.
To complete soil and herbage testing on-farm, contact your local PGG Wrightson Technical Field Representative.
1 Internal research conducted by Ballance Agri-Nutrients and undertaken by an independent contractor in the Bay of Plenty and Hawke’s Bay in 2008.