In stockless organic crop rotations, the absence of livestock, manures and long-term grass/clover leys pose significant agronomic challenges. A study in eastern England, from 1990 to 2000, on a productive silty clay loam soil previously in an intensive non-organic arable rotation, assessed crop performance in a stockless arable organic rotation. Performance of fertility building crops was very variable; establishment was affected by a range of environmental and other factors. However, this was not clearly reflected in the performance of following arable crops illustrating the over-riding impact of environmental conditions on organic crop performance, particularly on a fertile soil. Over the first full crop rotation, mean yields of winter wheat (Triticum aestivum) (7.3 t ha-'), spring wheat (Triticum aestivum) (4.1 t ha-') and spring beans (Viciafaba) (3.6 t ha-') were all above average for organic production in the U.K.. Foliar disease levels in combinable crops were generally very low. Damage from slugs (Deroceras reticulatum) and blight (Phytophthora infestans) contributed to very variable potato (Solanum tuberosum) yields (14.7 to 40.2 t ha-1 ). Soil available P and K tended to decline slowly with time but remained above levels likely to restrict crop growth.
By WILLIAM C'ORMACK. THE most reliable method for estimating this aldehyde is that of Flint and Tollens (Landw. Versuchs-Station, 1893, 42, 381), which is based on the production and gravimetric estimation of the phenylhydrazone. Their method, however, involves the use of a factor, which must be determined for the special conditions under which the estimation is carried out, as it varies with the concentration of the solution, amount of substance, &c. Further, since the phenylhydrazone cannot be heated above 60°, the time required to dry it to constant weight may amount to from one to three days, according t o the meana and apparatus available. The following method dispenses with the uee of a factor, and can be carried out in half an hour with a much
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