Sprinkler irrigation on clay soils in southern Finland IV. The effect of repeated applications of water and nitrogen fertilization on spring cereals

Abstract

In 1967 and 1968, in the month of June, irrigation of silty clay soil in southern Finland by a single sprinkling, which involved the application of 30 mm of water, increased the yields of spring wheat by an average of between 880 and 970 kg per ha, or 37—51 %, and the yields of barley by 1140—1340 kg per ha, or 37—42 %. Repeating the irrigation after about one week further increased the wheat yields on the average by from 670 to 800 kg per ha and the barley yields between 810 and 860 kg per ha. The effect of the irrigation on the size of the yields was virtually of the same magnitude both years in spite of the fact that in 1967 both June and July were extremely dry months, whereas in 1968 the dry June was followed by a rainy July. The sprinkling affected the ripening of the grain, on the other hand, differently each year: slightly retarding the ripening in 1967 but considerably hastening it in 1968. In the latter year, the irrigation prevented detrimental late tillering and thereby augmented the hectoliter weight and 1000-grain weight of the crops. In response to the one-time sprinkling, the protein content of the grains decreased in the case of the wheat by an average of 1.0—1.3 and of the barley by 0.1—0.7 %-units. The effect of two sprinklings was corresponding decreases of 1.9—3.1 and 0.8—1.0 %-units. The application to the seedlings as surface dressing immediately before irrigation of calcium nitrate containing 60 kg/ha of nitrogen increased the protein content of the wheat on the average by 1.6 and of the barley by 1.9 %-units. The nitrogen fertilization thus prevented excessive lowering of the protein content by irrigation and, furthermore, considerably intensified the salutary effect of the irrigation in augmenting the yield. A disadvantage of abundant nitrogen fertilization was a slight retardation of ripening. The placement of basal dressing with a fertilizer drill at a depth of 9 cm proved effective, particularly in 1967, when both the wheat and the barley yields increased 22 per cent in comparison with the effect of surface dressing. Use of the fertilizer drill, moreover, promoted the ripening process. Sprinkling did not appear to reduce the placement effect of the fertilizer; rather did these two methods form an exceedingly favorable combination.