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PRACTICALITY AND LONGEVITY OF HARDPAN MODIFICATION 



Peter L.M. Veneman 

 Department of Plant and Soil Sciences 



About 40% of the soils in Massachusetts have a hardpan within 3 ft of the soil surface. 

 Considering the fact that a large number of our orchards are located on drumlins 

 (elongated or oval hills of glacial drift), I estimate that between 50 to 60% of the 

 Massachusetts orchard soils have a hardpan within 3 ft depth. The presence of this 

 pan is well known to most fruit growers as it often necessitates sub-surface tile drainage. 

 The low water permeability is due to a high bulk density of the pan material. This often 

 inhibits root proliferation as well, which may result in increased susceptibility to 

 midsummer droughts and excessive frost heaving during the winter. 



Modern, size-controlling rootstocks seem especially sensitive to the presence 

 of this hardpan. The dwarfing effect not only occurs above-ground, but is also evident 

 from a less prolific root system as compared to that of standard rootstocks. In addition, 

 size-controlling rootstocks such as M7a are in full production after about 10-12 years, 

 while the standard trees take much longer to become productive. The longer time period 

 permits the establishment of an extensive root system before this becomes strained 

 under the demands of a maturing fruit crop. Even though economic conditions dictate 

 the need for early production, tree vigor and the need to sustain long-term production 

 capacity necessitate the establishment of a healthy and extensive root system prior 

 to the onset of production. 



This article reviews the pertinent literature concerning the long-term persistence 

 of soil profile modifications and discusses practical methods which may improve root 

 vigor of fruit trees in hardpan soils. 



A variety of experiments have been carried out in past years to evaluate the effects 

 of soil profile modification on drainage, water availability, frost heaving and crop yield. 

 In general, the deeper and more extensive the initial soil disturbance is, the better the 

 results (Unger 1979). Various experiments (Mech et al. 1967, Bradford and Blanchar 

 1977) found that mixing the top soil with sub-surface layers, and additions of lime, 

 fertilizer or even sawdust significantly increased yields of alfalfa and sorghum. It is 

 reasonable to assume that such an improved growth environment also will foster the 

 development of fruit trees, both above and below ground. Recent research reports 

 (Unger, 1979) stress the importance of mixing the topsoil with the subsoil to obtain lasting 

 results. Studies in New York indicated that modification of a hardpan by mechanical 

 disturbance alone, resulted in re-establish ment of dense soil layers in less than 11 years 

 while buried topsoil remained less dense even after that period (Fritton and Olson, 1972). 

 Researchers in Pennsylvania found that additions of organic matter wiU delay the 

 soil's return to its original bulk density for a period of 7 to 8 years (Fritton et al. 1983). 

 That study also reported the ineffectiveness of subsoiling and deep tillage when the 

 topsoil was not mixed with subsoil. 



The use of topsoil from old orchards for new plantings may be less desirable when 

 the soil is suspected to contain large numbers of nematodes. Thorough mechanical 

 mixing may reduce the nematode population susbstantially (R. Rohde, personal 

 communication). Use of non-orchard topsoil, hay or peat will prevent a nematode problem 

 and give the young trees a head start, although this method probably is more costly. 



