A Long-Term Manurial Trial on Dessert Apple Trees

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Abstract
A factorial NPK fertilizer trial was started in 1931 with newly planted dessert apple trees. Two varieties (Cox’s Orange Pippin and Beauty of Bath) and four rootstocks (M.I, M.V, M.IX and M.XII) were represented. By 1953. after the orchard was thinned in two stages, only one experimental tree, of Cox’s Orange Pippin on M.XII, remained in each plot; at this time a fourth factor was added by establishing a sward (S) in half the plots and continuing to cultivate the remainder during each spring and summer. Severe deficiency symptoms developed early in the trial on plots receiving no potash. Recovery followed the overall annual application from 1937 of 2 cwt. per acre sulphate of potash, additional to the treatment comparison of nil v. 2 cwt. per acre, but large differences in tree size and cropping persisted. These differences were not greatest with the variety or the rootstock showing the most severe leaf scorch symptoms. The overall potash application was discontinued in 1953, but the levels of “ available” potassium in the soil had by then been raised, and the trees of Cox on M.XII did not develop potassium deficiency over the next ten years. On the contrary, there was evidence that the higher level was now harmful, perhaps because of induced incipient magnesium deficiency. Superphosphate (18% P2O5, 5 cwt. per acre per annum) did not affect the performance of the trees and only slightly increased the phosphorus concentration in the leaves. Much greater increases in leaf phosphorus were brought about by grassing down, particularly in the absence of nitrogen applications. In the nitrogen treatment sulphate of ammonia was applied initially at 1½ cwt. per acre per annum, but this rate was increased to 3 cwt. per acre in 1941 and then to 6 cwt. per acre in 1953 ; from 1958 Nitrochalk at an equivalent rate was applied instead of sulphate of ammonia. This nitrogen treatment increased the total crop per plot over the first I7 years by 15%, and the total crop of the Cox on M.XII over the period 1953-62 by 25*#x0025;. The response was especi~lly marked in the last few years when the trees with and without nitrogen were still virtually indistinguishable in leaf colour ; values for nitrogen concentration on a dry-weight basis in mid-shoot leaves for August 1962 were 2·9% and 2·8% respectively. Trees receiving nitrogen were grassed down in 1953 without reduction in total crop over the next ten years, though nitrogen status was depressed in the first few seasons. This depression was much more severe and persistent with the trees not receiving nitrogen, despite the abundance of clover in the swards on those plots. The advantages of grassing down on fruit quality may be largely due to the restriction of nitrogen supply to the tree.

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