Study Of Potato Handling On Farm

Press, Volume XCVIII, Issue 28890, 9 May 1959, Page 8

Study Of Potato Handling On Farm

Digger damage to potatoes becomes more apparent after the tubers have been held in store for a time or are submitted to washing so that field assessments of damage are not strictly accurate. This point is made by Dr. I. D. Blair, head of the microbiology department at Canterbury Agricultural College, in a college technical publication in which he sums up the results of a study made during the last three potato seasons of factors which cause loss and damage in the handling of the potato crop on the farm and in transportation of potatoes to the North Island.

In the course of the survey a sample of Canterbury crops was inspected during the lifting period in May and June, farm consignments were inspected during grading in produce storesand aspects of transportation were observed.

Of digger damage Dr. Blair said that his figures which showed that in 1956 17 per cent, of the sample crops suffered with an average level of 6 per cent, of tubers affected, and in 1957 13 per cent, of crops at an average level of 9 per cent, of tubers indicated a level of damage that was lower than expected by observers who contended that mechanical bruising of tubers during lifting was a major problem. But Dr. Blair said that usually damage from the digger was in the form of superficial and skin-deep bruises and that in the store 5 to 8 per cent, more digger damage was apparent than in the field. This had been further underlined by the introduction of potato washing in that consignments of potatoes which appeared to be free of damage on delivery to store have been shown after washing to be severely bruised, a result seemingly not associated with the actual washing process.

Peeling Loss On tlje other hand he said that whatever the actual amount of digger bruising it was doubtful whether this kind of marking would lead to anything like the loss from peeling or paring which occurred with mishapen tubers. There was evidence of up to 25 per cent, peeling loss in some varieties (e.g. Dakotas) almost entirely connected with the poor shape of the tubers.

Digger bruising, nevertheless, had to be deemed important in the sense that these bruises provided a point of entry for the destructive dry rot fungus, a major cause of loss in tubers intended for long storage. The experience and care of the digger operator were found to play a major part in the elimination of damage at this stage. One instance of 20 per cent, digger damage in 1956 and another of 30 per cent, damage in 1957 were clearly caused by driving the equipment at a speed of more than three miles an hour through stony soil. Bruising also occurred when only small amounts of soil were carried over the elevator chains, which was associated with digging in soils of light and dry texture.

Dr. Blair also found that where crops were graded on farms with

farmer’s or contractor’s equipment there was room for improvement. The evidence of unsatisfactory farm grading leading to severe damage had come from the returns of a major commercial firm which had received farm-graded potatoes for washing. Up to 97 per cent, of damaged tubers were recorded in some lines graded on the farm compared with 25 per cent, damaged for portions of the same consignment that had not been passed over the grading riddles on the farm. The amount of dirt going forward in sacks of potatoes had become a matter of particular concern, said Dr. Blair, 10 per cent, of 118 consignments being removed in 1957 and 4 per cent, of 66 consignments in 1956, the wide difference being accounted for by the very wet soil condition during the harvesting period in 1957. Individual consignments from farms had contained as high a proportion of dirt as 33 per cent. The Dakota variety, in accord with its irregular surface and predisposition to second growth, carried much more dirt than other varieties.

The proportions of adhering soil had meant that even after grading the surfaces of tubers must have been dirty and soil encrusted. Many North Island purchasers of South Island potatoes had testified to that and they now had the opportunity to compare such potatoes with lines that had been washed, waxed and packaged in a manner to induce high consumer appeal. The most serious consequence of dirt had been the manner in which soil covering at grading had obscured or even tended to camouflage surface defects that had thus evaded detection by graders.