Old and modern wheat cultivars compared on the Broadbalk wheat experiment

The grain and straw yields and nitrogen contents of an old and a modern winter wheat cultivar were compared on a series of plots on the Broadbalk wheat experiment at Rothamsted Experimental Station, England, over a three year period. The plots had received amounts of fertilizer nitrogen ranging from 0 to 288 kg ha-1 and, except for one, all had received ample amounts of phosphorus, potassium and magnesium fertilizer. In each plot, the plants in a 2.0 × 2.0 m area were supported to prevent lodging, those in the remaining area being non-supported. Different sections of the experiment allowed rotational and agrochemical treatments, and their interactions with plot, i.e., nitrogen fertilization, and cultivar, to be assessed.

Overall, Brimstone, the modern cultivar, yielded 52 per cent more grain than Square Head's Master, the old one. Both absolutely and proportionately, Brimstone yielded more grain at the higher levels of nitrogen fertilization than did Square Head's Master. Lodging did not appear to reduce the yield of the old, tall, Square Head's Master. Nitrogen fertilization greatly increased shoot biomass at maturity, but at any given level of nitrogen fertilization, the biomass of the two cultivars was virtually identical.

Because of the greater harvest index of Brimstone, and despite the lower nitrogen concentration in its grain, its grain from unit land area contained more nitrogen than did that of Square Head's Master. Accordingly, the apparent recovery of nitrogen by the grain of Brimstone was greater than that of Square Head's Master. It was calculated that less land and fertilizer nitrogen would be needed to produce a tonne of grain with Brimstone than with Square Head's Master. However, the apparent loss (non-recovery) of fertilizer nitrogen in intensive wheat growing was estimated to be greater at high than at low levels of application, whether or not straw was incorporated into the soil.