Environmental modifications resulting from the culture and grubbing of trees.
After a mature apple orchard had been removed by grubbing the trees various experimental treatments (different systems of manuring and ploughing at two depths) were applied to the site. Apples were again planted, at a closer spacing, 3 and 7 years after the orchard had been grubbed and a succession of arable crops had been grown on the site. From the appearance, growth and cropping of the mangolds grown immediately after grabbing, and of the apples planted later, and from the effects thereon of experimental treatments, the effects on the environment of the culture and grubbing of trees were assessed. It is suggested that: (1) The original trees had progressively reduced the nutrient content of the soil, to produce a fertility gradient radiating outwards from the site of each original tree. (2) The effect of additional sulfate of ammonia on mangolds was small on the sites of the original trees, which suggests that the population of nitrifying bacteria in the soil immediately below the trunks of those trees may have been reduced, so that subsequent crops could not respond to sulfate of ammonia in these localized areas. (3) The passage of farm machinery had compacted the soil in the alleyways which formed the regular routes through the orchard. (4) The mechanical disturbance involved in grubbing a tree had little effect on the deep soil of the site, but it could be more important on a shallow soil.-E. Malling Res. Stat., Kent. Climatic factors. (See also 2591, 3054.).