Test digs increase spud crops value
By Andrew Swallow
POTATO growers should do more test digs to make sure they get maximum value from the crop, says SAC.
"Sampling and test digging is time well spent," says agronomist Eric Anderson. "But you must do sufficient digs for it to be accurate."
Even in apparently uniform fields, substantial variation in crop yields can occur across the field. Test digs should be taken from at least four points in fields up to 6ha (15 acres) or six in larger fields, he advises.
"Any less than that and predictions can be wildly out. Growers end up surprised by what is in the shed after lifting."
Initially, look-see digs are sufficient, but as soon as tubers are found approaching the top riddle size, formal digs of 3m along drills, or 2m along beds, should be done to determine optimum burn-down time.
"The date of burn-off is critical. Growers should aim to maximise the yield and value of target fractions."
Allowing for post-defoliation tuber growth is important to do that. "Tubers will grow by 2-5mm after burn-off." That should increase crop value but in some cases, such as salad potatoes for punnets, may make the crop too big, he warns.
After burn-down, test digs can provide growers with valuable information on skin disease development, such as black dot, silver scurf or rhizoctonia. Yield forecasts can also aid harvest planning. *
• Fields under 6ha: 4 digs min.
• Fields over 6ha: 6 digs.
• Dig 3m in drills, 2m in beds.
• Yield t/ha = Average weight of digs x 1000/Length of dig (m) x drill or bed width (cm).
• Grade out.
• Calculate value by size.
• Allow for post burn-down growth.