Growers report yield has been decreasing each year. In other crops growers have the ability to utilise the genetic gain from breeding but in potatoes, as there is very little change in cultivars, any yield improvement has to come mostly from agronomics.
Yield Gap Project
Led by Plant and Food Research (PFR), the focus was to identify the factors responsible for reducing yields in potatoes.
The first year results included some modelling work to identify yield potential at each site linked to a survey of process potato crops in Canterbury. This showed that the yield gap was often over 30t/ha with top yields being 66t/ha. It was found that nutrients were generally not limiting and that foliar diseases were well controlled. The research to date has indicated that soil constraints and particularly soil borne diseases are reducing yields.
The results indicated that the major soil borne disease was Rhizoctonia (both AG2.1 stem canker and AG 3 tuber canker were present) and although new ground (potatoes only once in 10 years) had less disease there was not a marked difference in yield between new and old ground. The crops in rotation do appear to be influencing Rhizoctonia with less disease following grass than following wheat.
Spongospora (powder scab) root galling was also common. Nematodes (potato cyst nematode PCN (Globdera) and root knot (Meloidgyne) and root lesion nematode (Pratylenchus)) were reported in crops but the impact on yield is not clear.
- Quantifying the potato yield gap – three case studies in Canterbury
- Yield Gap Project Summary
- Sarah Sinton – Potato Yield Gap 2013-14
- Striving for maximum potato yields in Canterbury
Soil Quality – Compaction
Compaction has been identified as being a problem and a value of 1.5 MPa has been identified as a critical factor above which yield is reduced. Although it was identified that compaction reduced yield the research has not identified what aspects of crop management are causing compaction or if yield loss is directly due to compaction or to the impact of compaction on plant water use or irrigation management.
FAR were successful with an application to MPI SFF. The project will run for three years (from 2015) in Pukekohe, Manawatu and Canterbury and focus on ‘Increasing potato yield through understanding the impact of crop rotations and soil compaction’.
Year 1 is well underway with eighteen commercial potato field crops being evaluated for this season. The desired outcome of the project is to better understand where potatoes fit in the rotation, how to reduce soil compaction and improve soil structure whilst understanding how all these factors impact of soil borne diseases. Comprehensively testing abiotic and biotic factors along with understanding the rotation and soil borne diseases over three years will give us the full spectrum of how and where potatoes fit best along with understanding where we can increase yield.
In Paddock Variability.
The yield gap project has identified large in paddock variability with up to 90t/ha in some parts of some paddocks.
The use of guidance technology and variable rate application based on soil testing is being undertaken but there is limited crop based management of inputs. There may be opportunity to manipulate some inputs. In paddock variability can be relatively easily identified using remote sensing equipment (both NDVI and Infrared) but there are three major problems with potatoes which are:
- Remote sensing can identify differences in a paddock but these need to be ground truthed to determine what the reason for the difference is – e.g. canopy disease etc.
- Often by the time a difference is apparent on a crop sensor map, even when it is ground truthed, growers cannot implement a management decision that will change the crop performance.
- Yield maps are generally used as the baseline reference for Precision Agriculture and this is difficult and expensive to implement for potatoes.
Crop Rotations – Bio-fumigant Crops.
There is a significant amount of international data which outlines how different crops in a potato rotation influence the incidence of a range of pests and a limited amount of data on how these crops impact on yield. In New Zealand, and elsewhere in the world, there is interest in biofumigant crops, such as Caliente Mustard, with limited data on how they influence diseases and pests or crop performance, thus it is not clear if or when growers should use these crops to maximize the value of a cropping program. The theory is that these crops produce gucosinolates that through enzyme action produce bioactive isothiocynates and these control these diseases.
There are two major programmes internationally looking at biofumigant crops in potatoes, one in the US and one in the UK. The UK programme only commenced in March 2014 and appears to be well funded and long term.