Nutrient uptake and distribution by bread and durum wheat under drought conditions in South Australia

A. Zubaidi, G. K. McDonald and G. J. Hollamby 

Abstract

Summary. An important limitation to the production of durum wheat in South Australia is its poor adaptation to the alkaline, sodic soils of the cereal belt, which often results in nutrient imbalances in the crop. A field experiment was conducted at Palmer, South Australia, to measure the nutrient uptake and distribution between grain and straw of 3 bread wheat cultivars and 9 cultivars and breeding lines of durum wheat. The purpose of the work was to characterise the patterns of nutrient uptake and to examine whether there were major, consistent differences between bread wheat and durum wheat. Rainfall during the growing season was below average and the crops suffered from drought stress after anthesis.

Plants were marginally deficient or deficient in nitrogen (N), phosphorus (P) and zinc (Zn), and boron (B) concentrations were high. Compared with bread wheat, durum wheat had a very much higher concentration of sodium (Na), higher concentrations of calcium (Ca) and sulfur (S), but lower concentrations of potassium (K), magnesium (Mg), manganese (Mn) and copper (Cu). Total amounts of P, Zn and Na in the shoot continued to increase throughout the growing season with significant increases occurring during grain filling, whereas there was little increase in the amount of N, K, B and Mn during grain filling. The maximum rate of nutrient uptake occurred before the time of maximum crop growth rate, and was in the order K (10.1 weeks after sowing), N (10.6), P (11.3), Mn (12.0), Zn (12.5) and B (14.6); maximum growth rate occurred at 14.8 weeks. There was no consistent difference between bread and durum wheat in the partitioning of nutrients to the grain.

The importance of N and Zn uptake to the growth of the durum wheat genotypes was shown by significant correlations between maximum uptake rates of these nutrients and maximum crop growth rate, with the strongest correlation being with Zn. Growth rate was not correlated with uptake rates of other nutrients. A number of genotypes of durum wheat had maximum rates of Zn and Mn accumulation up to twice those of the current commercial genotypes. Some of these lines have yielded well at Zn- and Mn-deficient sites which indicates that the micronutrient efficiency of durum can be improved.

Late in the season the experiment showed signs of infection by crown rot (Fusarium graminearum Schw. Group 1). Durum wheat showed more severe symptoms than bread wheat and the number of white heads in durum wheat was inversely correlated with the concentration of Zn in the shoot during the pre-anthesis period.

Australian Journal of Experimental Agriculture 39(6) 721 - 732

Full text doi:10.1071/EA98185 

Shoot growth, root growth and grain yield of bread and durum wheat in South Australia

A. Zubaidi, G. K. McDonald and G. J. Hollamby 

Abstract

Summary. In South Australia, durum wheat yields more than bread wheat under well-watered and fertile conditions, but over much of the state’s cereal belt the yields of durum wheat, relative to bread wheat, are low. Three experiments were conducted over 3 years at 2 sites to compare the growth and yield of bread and durum wheat and to investigate some of the reasons for the differences in the relative yields of the 2 cereals.

Durum wheat yielded less than bread wheat when annual rainfall was less than about 450 mm or when the site mean yield for bread wheat was less than 250 g/m². Compared with bread wheat, durum wheat had poorer early vigour, which was associated with fewer tillers/m², and produced fewer kernels/m². Under favourable grain filling conditions, durum wheat produced larger kernels than bread wheat but its kernel weight was more variable across sites and seasons and consequently, the relative yields of the 2 cereals depended largely on kernel weight. For example, in a wet year, durum wheat yielded 20% more than bread wheat, despite producing 16% fewer kernels/m², because of its larger kernels (52 v. 36 mg). In 2 drier years, kernel weights of durum and bread wheat were similar (durum and bread wheat mean kernel weights: 40 v. 37 mg; 30 v. 33 mg) and so durum was unable to overcome the limitation of fewer kernels/m² and its yields were similar to or less than bread wheat.

Root length densities of durum and bread wheat below 30 cm were low. Durum wheat had an equivalent or lower root length density than bread wheat and lower length per gram of root dry matter, indicating less finely divided roots. This suggests that durum wheat may sometimes be less able than bread wheat to utilise moisture and nutrient reserves in the subsoil because of a smaller root system. This is an undesirable characteristic for a crop that appears to be more reliant than bread wheat on producing large kernels for high yields.

Efforts to improve the yield of durum wheat, either through genetic improvement or by agronomic means, should focus on reducing the levels of stress during the post anthesis period so that limitations to kernel growth are minimised. Improving the early vigour of the crop, having cultivars of the appropriate maturity and with adequate levels of resistance to root disease, and improving root growth and function in the subsoil are likely to be desirable characteristics.

Australian Journal of Experimental Agriculture 39(6) 709 - 720

Full text doi:10.1071/EA98184

© CSIRO 1999