New procedure for wheat sowing recommended

Press, 9 May 1980, Page 8

New procedure for wheat sowing recommended

The number of heads or ears in a given area has an important influence on the yield of a wheat crop and Ministry of Agriculture officers are recommending a sowing procedure based on seed numbers rather than weight to produce the number of plants to give the optimum number of heads.

Mr J. G. (John) Hampton, a scientist with the seed testing station of the Ministry of Agriculture at Palmerston North, and Mr B. L. (Bede) McCloy, a farm advisory officer (seeds) with the Ministry in Christchurch, said last week that they were not talKing about 10 tonnes to the hectare crops but of raising the average level of yields by about a half to a tonne per hectare. Workers at Lincoln College a few years ago found that differences in head population at harvest accounted for most of the variation in wheat yields in Canterbury. . Mr Hampton said that survey work done by Mr McCloy in Canterbury had shown that head population was one of the most important elements of yield in the province and on the basis of work done in the United Kingdom and at Lincoln and in Ministry • trials where wheat was autumn sown the evidence suggested it was desirable to go into the spring with 250 plants established per square metre. This meant that each plant could produce and maintain at least two or three heads to give the desired head population of about 600 per square metre.

For yields of more than five tonnes per ha a head population of 600 to 800 per square metre at harvest was required. The easiest way to achieve that population was to sow on a seed number basis, which involved a change from traditional

methods of sowing on a weight basis. The need for this change could be seen from an examination of the variation in the weight of 1000 seeds in New Zealand seed wheat lines and within the same variety. This became important where seed lines of different seed weights were sown at the same sowing rates.

Thus if a line was sown at 134 kg per ha it would produce more plants to a given area if the seed was small compared with where the seed was big. It was for this reason that sowing had to be changed to a seed number basis. This meant using the 1000 seed weight of the line and also an estimate of the expected field emergence,

which for autumn sown wheat in Canterbury could be taken as 70 per cent. All merchants, Mr Hampton said, now had a ready reckoner by which, given the 1000 seed weight and the expected field emergence rate of 70 per cent, the sowing rate required to establish the optimum plant population was given.

The concept of a recommended blanket sowing rate for Canterbury was now outmoded, he said. In future the seed testing station at Palmerston North will report the thousand seed weight for all machine dressed cereal seed samples submitted for testing. There will be no additional charge for this, which will be carried out as part of the purity and/or germination test.

Mr McCloy said, however, that where the 1000 seed weight of a seed line was not available a farmer could work this out for himself simply by counting out two lots of 200 seeds, weighing them and averaging the weight of the two lots and multiplying by five to give the 1000 seed weight. Indicative of the importance of achieving optimum head populations, in the 1978-79 season the average head population for 45 crops in North and central Canterbury was .390 per square metre and in 1979-80 the average for 27 crops in central Canterbury was 508 — still well below the optimum — but in 1978-79 in the top yielding crop of six tonnes per

ha the average number of heads was 622 and in the most recent season where the highest yield was 7.5 tonnes the average number of heads per square metre was 694.

Mr McCloy said that any increase in the sowing rate beyond the optimum would lead to a decline in yield because of inter-plant competition for moisture and nutrients and this resulted in a reduction in the number of grains per head and in the weight of these grains. He noted that apart from the head population the other components of yield were the numbers of grains per head and the weight of those grains and once the optimum head number had been obtained the other components became important to further increase yield. However, the .officers said that they wished to make it clear that the optimum populations they were talking about for wheat crops applied to medium tq heavier soils or lighter soils under irrigation. On lighter dryland areas it was possible that these soils could not support these populations — they did not have the information yet as far as they were concerned.