Precision farming: getting it wrong

The technological advances achieved over the past 10 years in utilising electronic and positioning technology to improve mechanised tillage practices help farmers to get the job done correctly and accurately. Marius Ras (M.Eng Mech; Pr Eng), Group Marketing Director, ROVIC LEERS (Pty) Ltd explains.

Machinery from the past was a bit like a motor car without dashboard gauges – you could drive it and reach your destination, but very little information was available about the route, the environment and the estimated time of arrival. The knowledge and skills of the driver/operator determined the outcome. Today, the technology exists and is in commercial use that gives the operator a “full dashboard” of information, actually controlling most of the functions that in the past were reliant upon the operator’s skills and knowledge. If and when the application of any technological advances gets to the point where the end user is “relieved” of the responsibility to understand and grasp the basics on which the process relies for optimal efficiency and productivity, the result could be that you could be getting it WRONG with PRECISION!

A layman’s definition of Precision Mechanisation: To know exactly what goes out of, or comes into a machine, and the ability to either control it to pre-programmed levels going out, or measure or record the parameters of the material coming in, whilst at the same time knowing the exact position where it occurred. The risks of getting it wrong if and when some knowledge of the basic principles involved are overlooked, will be demonstrated with three case studies:

Case study 1: GPS positioned, draught stress controlled ploughing

Machine capabilities:

  • GPS positioning and auto steer of tractor for a perfect ploughing cut.
  • Draught stress control determining optimal ground speed for minimal wheel slip and maximum field capacity at a given working depth.

Watch out for:

  • Why are you ploughing in the first place? The results of mouldboard or disc ploughing are:

– The vertical mixing of the soil profile, which effectively eradicates the natural organisms residing at the different soil levels, resulting in a soil profile with very little capacity to convert the ploughed-in crop residue to be composted.

– Nitrogen deficiencies in the ploughed profile with composting extended well into the growing season.

– Mechanical breakdown of soil particles because of the large surface contact area between die mouldboard / disc and the soil being worked. The fine soil particles, getting finer with every ploughing event, become compacted, forming a compacted surface layer after rain or irrigation.

– Plough banks are formed, creating a barrier to water penetration, resulting in waterlogging and wilting crops.

– Completely exposed soil surfaces resulting in excessive evaporation of moisture, as well as wind and water erosion.

  • The ONLY valid reasons why soil should be worked in some way are:

– To alleviate compaction layers, either on the surface or below, which resulted from above ploughing practises or surface traffic like animal grazing or vehicles.

– To aerate the soil during lime / gypsum applications to facilitate their movement into the soil profile after rain or irrigation.

  • The ONLY way to achieve the above without the negative effects of the ploughing practice is to aerate the soil with properly designed tine aeration equipment – and only used when either of the above conditions need to be alleviated. In most cases it would suffice to follow residue management practices and to use minimum tillage planters to take care of the rest.

Conservation farming practices take care of the existing soil, moisture and nutrients as a first objective, making them available in abundance and persistently into the future for the crops planted. Farming for our children, not for this year’s crop, is the strategy.

Case study 2: GPS controlled variable rate precision fertiliser spreading

Machine capabilities:

  • GPS positioning with fertiliser nrequirements pre-programmed according to yield potential charts.
  • Variable rate control according to spreading width and ground speed.
  • Variable spread width with section control.
  • Auto calibration.

Watch out for:

  • Correct mechanical machine height and angle on top link mount – set it according to operator’s manual specifications, make sure that stabilisers and top link are tightened and in the correct position. You are GUARANTEED to miss spots or overlap if you get this wrong!
  • Screen every batch of granular fertiliser to determine the fine particle component. You will experience a large overdose application in the close proximity of the driving line if the fine particle component does not fall within the required parameters!

Case study 3: GPS controlled variable rate precision herbicide spraying

Machine capabilities:

  • GPS positioning with variable rate chemical requirements pre-programmed according to weed pressure.
  • Variable flow control by pressure or impulse adjustment according to spraying speed and rate requirements.
  • Up to 20 km/h spraying speeds achievable.

Watch out for:

  • Boom spraying height consistency:

Nozzle overlap and efficiency of reaching the target rely heavily upon a consistent boom height of 500 mm (110 degree nozzles) or 750 mm (80 degree nozzles) above the target. A boom height increase of 400 mm beyond the required norm, potentially results in a 40% reduction of chemical active cover on the target. Exceeding spraying speeds that compromise this consistent boom height requirement, will result in bad chemical control of the weed and the potential build-up of resistance to the active ingredient.

  • Wrong nozzle pressure:

The flow control system will increase or decrease pressure to give the required flow as speed and weed pressure requirements vary. If this pressure exceeds or undercuts the optimum pressure range for the chosen nozzle, the system will warn the operator, but it can be ignored. With the pressure too high, in a quest to deliver the correct flow at the high speed, the target coverage will diminish rapidly, resulting in drift. At a too low pressure, the spray angle of the nozzle will decrease to a point where strip spraying will occur.

  • Poor agitation:

Centrifugal pumps are normally used on self-propelled sprayers to enable delivery of the high flow rates required for superfast spraying and agitation. The flow delivered by a centrifugal pump is inversely proportional to the pressure requirement. This could lead to circulation and agitation starvation in the tank when pressures required for a given flow at high speed is leaving too little bypass for agitation. The result could be filter and nozzle clogging or, even worse, non-uniform chemical concentration in the tank resulting in crop damage or bad weed control.

In the above case studies, the controlled parameters by the electronics, software and positioning systems would not have been able to even identify a problem, and the results could have been catastrophic – both in the long run and immediately! Good “old school” knowledge of the basics in agronomy, soil science, engineering and common sense are the real and only safeguarding against DECISION and PRECISION blunders. In this way DECISION FARMING (doing the right things – farming for our children) is executed by PRECISION FARMING (doing the things in the correct manner) to produce CONSISTANTLY into the future.

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ProAgri Zambia 10 – August 2016

Big players show top technology at Val Farmers’ day