Grains Research and Development

Date: 01.01.1999

Gems from overseas Pt 2

Precision farming, it's not all a bed of roses.

This is the second of a two-part report on farm management issues that will continue to challenge farmers into the 21st century. The overseas farm management study tour that generated this material was supported by an Industry Development Award from the Grains Research and Development Corporation.

Sustainable farming The Alabama cotton story

The history of cotton in Alabama, USA, is a graphic example of unsustainable farming. Much of the farming land in Alabama has been destroyed by farming and the land is now suitable only for growing pine trees.

Cotton in Alabama peaked in 1850 at 1.8 million hectares. Today there are 200,000 hectares. On other former cotton land Alabama now has some 1.6 million hectares of pine trees, the only crop which will grow on worn-out, eroded acid soils.

The soils in Alabama are mostly duplex soils with a loamy or sandy surface and clay subsoils. After 50-80 years of cotton, some 20-30 cm of soil and much of the nutrients were gone. The structural degradation which resulted from a loss of organic matter and topsoil set up a vicious cycle of increasing runoff, erosion and nutrient decline.

These problems were recognised back in 1896, when the 'Old Rotation' was started at Auburn University to examine sustainable cropping practices. This experiment is now the oldest continuous cotton experiment in the world.

Soil organic matter in plots of continuous cotton, fertilised with phosphorus (P) and potassium (K), but with no nitrogen (N), could not get much lower at 0.6 per cent (0.3 per cent organic carbon), but there is four times as much (2.4 per cent organic matter) where there has been a rotation that includes corn and a winter cover crop of legumes.

The yield of cotton is now in proportion to the organic matter, with 1.5 bales/ha for continuous cotton and no added nitrogen, rising to 4 bales/ha for a cotton-corn rotation with a winter legume cover crop. See table.

Continuous cotton 1896-1996
Selected treatments from a total of 13Soil lossOrganic carbonCotton yield
1. Cotton - no nitrogen250.31.3
2. Cotton - winter legume cover crop150.93.3
3. Cotton - nitrogen fertiliser200.72.8
4. Cotton - corn rotation + legumes + N141.04.0
5. Corn - Cotton - soybean rotation111.33.4

In 1997, 101 years after it began, the Old Rotation experiment in Alabama was changed to zero-tillage. Cotton grown using zero-tillage and rotations with a cover crop has almost no erosion.

Take-home message

Continuous cotton in Alabama using cultivation was not sustainable, even with fertilisers. A rotation with crops that produce more organic matter than cotton, combined with zero-tillage, will build soil organic matter and improve structure. The healthier soils have fewer nutrient and disease problems, and the cotton will hang on better during hot dry spells in summer.

The most sustainable and profitable systems in Alabama and Georgia are now using zero-tillage and growing two crops a year, with a rotation to avoid growing cotton continuously.

Fertility decline

The Cullars Rotation is an interesting trial of fertilisers on various crops of southeastern USA, which has now been running for more than 80 years. The trial is an omission experiment in which crops receive a mix of all nutrients, with one missing. The results show the differences in sensitivity to nutrients expressed by crops grown in successive rotations after each other.

Cotton is particularly sensitive to potassium and, without it, produces only 24 per cent of potential yield. Corn is sensitive to nitrogen, soybeans to phosphate and wheat to N and P.

Cullars Rotation - Auburn University 80-year-old fertility experiment

Yield expressed as a percentage of complete fertiliser treatment
No K24425660
No P61302922
No N78248324

Precision farming: a costly choice

Precision farming techniques, yield monitors, satellite navigation and computer software have been embraced by US farmers for a longer time than in Australia. Here is some of the feedback.

Some US farmers are questioning the cost of precision farming. Yield monitors with GPS are currently around $US 7,000, with software around $2,000. But the cost of learning and using the system could be in the vicinity of $10,000 if a reasonable value is put on a farmer's time.

It sounds good to be able to monitor variations in paddock performance and make applications of such inputs as lime and fertiliser at a variable rate across the paddock, but there are many problems in practice.

We know nutrients vary considerably across paddocks, but the problem with precision farming is to know whether nutrients are limiting yields or whether the highest-yielding areas of paddocks are low in nutrient, due to high crop removal. In some cases there is a need to put more nutrients on the highest-yielding areas and in other cases on the lowest-yielding areas.

High cost of soil sampling

Precision farming may require a large cost for soil sampling. Grid sampling is being used by some US farmers with one soil test per hectare. Precision mapping can help by analysing patterns in the field and direct sampling based on similar units. The sampling is then done by a vehicle or bike fitted with GPS, which can find the sites to be sampled on the ground and record accurately where samples were taken.

Another problem is the cost of variable rate spreaders which use satellite navigation. The machines cost around $250,000 and charge $US8-14 per acre, depending upon the type and amount of fertiliser being spread. Some farmers say that the whole process is costing them around $20 per acre and they would rather spend their money on more fertilisers than on the cost of variable rate spreading.

The responses and benefits from variable lime application are more consistent than for other fertilisers. In this case, the paddock is mapped for pH and the variable rate spreaders put the lime on where needed. It helps to make a paddock more even in pH, rather than put lime on at the same rate whether the soil needs it or not.

Jess Lowenberg, an economist with the Precision Farming group at Purdue University, Indiana, cites 11 economic studies of precision farming which identify a profit in only two cases and mixed results in another four, depending upon grain yield and prices.

Precision farming is coming, but there are many techniques cheaper than the move into the satellite-computer age. Most of the benefits may come from fine-tuning inputs and studying why differences in yield occur in paddocks, without the big costs of varying inputs according to paddock variations using header monitors, maps and variable rate fertiliser application machines.

Management in the 21st century

Trends to challenge farm managers

  1. Global market competition, with low prices due to a general oversupply of food products.
  2. Increased market volatility, combined with market deregulation, places more onus on farmers to develop marketing strategies.
  3. Government support for agriculture is declining, but this is affecting farmers in other countries with higher support levels more than it is here.
  4. The 'Information Age' is now providing an electronic information explosion and information overload for farmers.
  5. Agriculture is becoming industrialised, with more vertical integration and corporatisation of the procurement, distribution and marketing of food.
  6. Advances in biotechnology, such as BT cotton, Roundup ready cotton, soybeans and corn are assisting farmers around the world to produce more efficiently.
  7. Environmental issues are assuming more importance, particularly those related to water quality and food safety.
  8. Agriculture is more than food. Pharmaceuticals, fibre and industrial products (e.g. starch, ethanol) are becoming more important.
  9. Precision farming is a suite of new technologies (yield monitoring, satellite navigation and computer mapping) that will help farmers fine-tune their production systems.
  10. The farm manager needs to become more 'professional' and spend more time on managing information, marketing, new technology and consumer-related issues.

Region North, South, West