Wheat Yield Response To Irrigation

Press, Volume CVI, Issue 31316, 11 March 1967, Page 8

Wheat Yield Response To Irrigation

Although the last season was a good one for wheat with rainfall well spread over the growing period—it could hardly have been better—where trial areas at the Winchmore irrigation research station were irrigated three times the yield was about 20 per cent better than on similar unirrigated country.

If a response of this order could be obtained in a comparison between wheat growing under dryland conditions and under irrigation in a season that was so favourable for dryland wheat, it is likely that the margin in favour of irrigation in a more typical Canterbury season would be even more marked.

Details of the Winchmore trial on Lismore stony silt loam were given this week by Mr E. G. Drewitt, a technical officer at the station.

The trial was in two parts on two two-acre blocks. On one block the crop followed potatoes and on the other block it was on country that had been in pasture for a long period—possibly as far back as 1951. These areas are on part of the 27-acre experimental cropping farmlet on the station.

Sowings The sowings were made on June 16 with 1091 b or a bushel and three-quarters of Aotea seed to the acre. On the area out of potatoes lewt of superphosphate and lewt of sulphate of ammonia were also spread at sowing, and later on October 5, because the wheat looked a bit yellowish, a further lewt of sulphate of ammonia was topdressed on to this area and it improved in colour as a result Where the wheat was sown out of grass no fertilisers were used at all. In early August, when the

seedling wheat was about three inches high it was rather severely frosted but it recovered and at the end of the same month it was affected but the frost was less severe on this occasion. Treatments

On each area there were two irrigation treatments, on of course the border dyke system. Part of each area was left dry as a control. This was known as Treatment I. Treatment No. II was prescribe! as irrigation at the tillering and at the milk stages. This treatment, Mr Drewitt said, was intended to simulate actual farmer practice. At this time of the year —in October, November and

December—demand for water was fairly heavy and it was felt that two waterings would be about what a farmer would be able to fit in in this period. Actually they were interested in defining when plants needed water most and whether there were stages where soil moisture could fall to the point where plants were at wilting point but they were not seriously affected.

In practice they had not watered at the tillering stage because it was then wet, but they had irrigated the appropriate trial areas in the late tillering stage, which was the first occasion when it started to get dry. It had also been intended that the second watering should be done at the milk stage, but if they had waited till then the wheat would have suffered a severe check, so the second application of water had been given at late flowering.

The other, or No. 11l treatment, involved irrigating when the soil moisture fell to 15 per cent and in this season this had meant three irrigations. When soil moisture falls to 15 per cent on these soils some three-quarters of the available moisture has been lost through evapotranspiration and this is equivalent to a soil moisture deficit of 1.8

inches. On the land out of potatoes Mr Drewitt said that irrigation dates for the treatments had been as follows: Treatment II: October 26 and December 16. Treatment III: November 1, December 4 and December 22. Wilting Point In early November Mr Drewitt recalled that on the non-irrigated treatment soil moisture levels had fallen to about wilting point But for the rest of the month there had been no moisture shortage. However the moisture position returned to wilting point again at the beginning of December and this was the position also from about December 14 through until December 29.

The dates that irrigation had been applied to the area out of grass had been about the same as for the former potato ground, Mr Drewitt said. Because it was a very wet year for wheat all of the plots grew well, but in the case of the irrigated treatments, because the wheat here produced more leaf, it showed more mildew and leaf rust, but Mr Drewitt does not think that from a yield point of view this was of much importance.

There were also Argentine stem weevil and Hessian fly throughout the trial, but here again not a great number of plants were affected. Irrigation did tend to retard maturity. This was particularly the case with the wheat in treatment 111. It was still in the flowering stage when it had its third irrigation and this tended to prolong the flowering. Mr Drewitt said that the wheat in the dryland plots and also treatment H came to maturity about the same time, but that in treat-

ment 111 would be about a week later. The dryland areas and treatment II were ready for heading towards the end of January and the whole trial was harvested at the one time on February 1. The yields were (in bushels per acre):

Bushel weights were higher on the area out of grass. On this area they were on average 621 b on treatments I and II and 611 b on treatment 111. Where the ground had been in potatoes the average bushel weight was 601 b in treatment I, 591 b in treatment II and 57jib in treatment HL In the latter case the grain was smaller and less well filled. Mr Drewitt said it was also noticed that the grain from the non-irrigated land was a little plumper and of a lighter colour than from the irrigated plots. The wheat from treatment 111 was rather more pinched and darker in colour than in the case of treatment 11.

As yet baking scores had not been obtained for the wheat from the various treatments.

Reviewing the trials, Mr Drewitt said it had been a fairly wet year and therefore a good year for wheat, yet even then an extra 11 bushels had been obtained with three irrigations. The fact that the non-irrigated area at times had been back to wilting point and very dry had affected the yield. It looked as though to get the best out of wheat it was desirable not to let the soil get dry. The wheat in treatment II in spite of having two irrigations still had to contend with dry periods.

After After Pots Grass Treatment I „... 57 52 Treatment II .... 61 59 Treatment III .... 68 63