We have a group in Hawke’s Bay focused on best management for field cropping.  We want to know how far we can push production without degrading the soil, our base resource.

We have drafted a five year cropping programme, based around process crops, but with other crops in the mix. This is typical in the region where process crops are mixed with onions, squash, some cereals, occasional potatoes and often winter grass.

In our programme we have tried to eliminate animals and pasture, looking instead at maximising vegetable production. Given the different seasons, season lengths and the realities of planting dates that must fit factory schedules, this gets a bit tricky.

Central to our plan are vining peas and green beans, two crops with specialist harvest equipment. Viners are very heavy. The bean harvester weighs in at about 18 tonnes plus 4 tonnes of crop when full. The pea viners are around 22 tonnes, plus a couple more of crop when full.

These machines have large wheel or track footprints, so impact a wide path. And pea viners typically travel across the lie of the crop, not up and down rows, so can track anywhere. How does that fit our plans to adopt controlled traffic!

Gary Cutts of Tasman Harvester Contractors is at the centre of the action. The company currently has nine harvesting machines with a price tag of around $1million each. From December, the machines earn their keep, harvesting 24 hours a day, seven days a week.

Peas are a very delicate crop and only have a premium harvesting window of 24 hours. Before that they’re too young, and after that they’re too old. It’s an exact science to determine when to pick.

For a successful harvest Gary’s team must respond to demand from the factory and deliver on time. Delays that affect factory processing are costly.  

The new harvesters, especially those on tracks, can get on to the ground even in very poor weather. But what is their impact on the soil? They are very heavy, they have big feet, and the soil may be weakened by wetness.

Gary contacted Marc Dresser at Landcare Research after hearing him at a LandWISE Conference. Marc is a specialist in soils and mechanical engineering whose knowledge is unrivalled. He worked with Gary on tyre selection and tyre pressures to optimise performance.

Together they reduced harvester tyre pressures from around 30psi to 20psi. They reversed the direction of jockey bin tyres too. Gary says the difference is immediately noticeable in the field. Coupled with a change to tracks, the soil load has been greatly reduced.

Gary still wants to know what the impact on the soil is. Are harvesters doing damage? If they are causing compaction, what is best practice remediation? When should it be done? How does it impact following crops?

We want to know too. And we want to know what a farmer can do to best prepare their soils before the harvesters arrive. Before the crop is even planted.

We can control traffic in pretty much all operations with the equipment in use now – except for the viners. We’ve looked at a number of scenarios, which suggest that the 30” row is the factor that sets the standard. Smaller tractors might straddle two rows, bigger machines can straddle four. If equipment is sized accordingly, we can get the trafficked area down to about 17% of the ground. Except for the viners.

Most paddocks only see peas about once in five years, so that leaves 4 years and 11 months of controlled traffic. But in our super-intensive farm, we might see peas almost every year and green beans too. We really do need to know how to manage this aspect of some of our important regional crops.