Guest Post: Dr Paul Johnstone (Plant and Food Research) on Improving Profits by Reducing Surface Ponding

Ponding of surface runoff from rainfall and irrigation can reduce crop production. The ‘Holding it together’ project addresses this.

Plant & Food Research and LandWISE are working with growers on ways to reduce surface ponding, improve soil quality and increase returns.

MAF Sustainable Farming Fund, Fresh Vegetable Product Group, Potatoes NZ, Hawke’s Bay Regional Council, Horizons Regional Council, Auckland Regional Council, Environment Waikato and Ballance Agri-Nutrients have funded the project.

Runoff occurs when water infiltration is slower than application of rain or irrigation. In some soils, slow infiltration is due to texture, in others it is reduced by frequent tillage or compaction. Whatever the cause, runoff can pond for extended periods, in low-lying dips or field edges. This ponding can be damaging to crops.

Trials with onions have shown that even temporary ponding can reduce yields. Yield loss ranged from 60-80%.  Ponding also reduced the proportion of yield within the most profitable size range.

In one field, a leaky pipe resulted in ponding during irrigation. This area of 0.2 ha cost the grower $1,700 in lost income. The cost of fixing the pipe was $10.

A  similar-sized area was affected by ponding during spring rainfall. Resulting crop loss totalled $3,500 in lost income.

Other crops dislike wet feet too, especially during germination, emergence and early growth, when ponding can affect establishment and final yield outcomes.

Weeds and soil-borne diseases can also flourish in affected areas.  Mobile nutrients, such as nitrogen, are easily leached beyond shallow root zones, resulting in potential deficiency. In worst cases, crops require replanting.

The project also looked at the grower’s greatest asset – their soil. Soil condition proved to be poorer in ponded areas. In particular, aggregates became clumpy, and soils heavily compacted.  When aggregation and structure collapse, soils become poorly drained and aerated, access to nutrients and water is restricted, and this reduces yield.

Nutrients and productive topsoil also concentrate in ponded areas after runoff.  In ponded areas, soil Olsen P levels were as much as 75% higher than adjacent unponded areas. Organic matter levels were higher too. This can contribute to variability and input inefficiency over time.

Furrow diking is a tool to reduce surface runoff. Small soil dikes (dams) are formed in wheel tracks by a towed implement. Controlling runoff largely eliminates the impacts of ponding, meaning better returns.

Horowhenua grower, John Clarke has seen how effective diking can be. In the past, ponding has reduced yields in low-lying areas. Where they tested diking there was no standing water after heavy rain, this is a major improvement.

Hawke’s Bay grower Scott Lawson of True Earth Organics, is also an advocate. “Diking eliminates ponding damage and can reduce disease incidence. It’s standard practice now”.

Growers may also harvest more rainfall with diking installed, as water has more soaking time and so more storage in the soil.

Scott Lawson notes that soils need to have good drainage. “sustainability of farming operations includes promoting good soil structure, by building organic matter levels, reducing cultivation and working to eliminate compaction”.

For more information on ‘Holding it Together’ projects or on implementing practices on-farm please contact Paul Johnstone (Plant and Food Research) or Dan Bloomer (LandWISE).

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