Nutrient composition of the produce of the Broadbalk continuous wheat experiment I. Changes over seventy years

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Abstract
1. A rapid extraction procedure of dried and ground plant material has been used in conjunction with the Lundegårdh flame method of spectrographic analysis. The accuracy of the analysis has been estimated, and the method has been shown to be comparable with ashing and gravimetric analysis.2. The effect of fertilizer treatment on yield and on the nutrient composition of the crop has been outlined. The changes which occurred in the period1852 to 1921 have been summarized by linear regressions fitted to 10-year means.3. The recovery of potassium was estimated, and the exhaustion or accumulation of potassium was shown to be related to exchangeable potassium in the surface soil.4. Sodium and magnesium sulphates used as fertilizers were shown to increase crop yield by increasing the potassium supply to the crop. It has been shown that the extra potassium came from non-exchangeable forms.