21- 



Soil Management 



Soil-mulch systems . When apple trees are heavily mulched, it is 

 necessary to adjust fertilizer programs, especially aTter the 

 mulch commenced to decay. While the material applied as mulch 

 varies considerably in chemical content, the average hay mulch 

 contains approximately 1% N, 0.41 P, and 1.3% K. On this basis, 

 33 pounds of hay mulch is equivalent to 1 pound of ammonium 

 nitrate in respect to the N added to the soil. The heavy appli- 

 cation of mulch eventually adds large quantities of K and N to 

 the soil. In addition to adding K to the soil, mulch makes more 

 readily available the soil's reserve supply of K. 



Mulching presents a dilemma in regards to nutrition. Hay 

 mulch can suppress grass and weed growth, improve soil structure, 

 conserve moisture, and is a source of N and K. Calcium mobility 

 might be greater under mulched trees becaus'e this element is 

 carried by water. High K is favorable for red color development 

 and the need of this element is high in heavy- cropping trees. 

 In contrast, high K can suppress Ca uptake and mulch might pro- 

 vide excessive N. 



Cult ivation . This system of soil management is generally practiced 

 only in young plantings when land has been cleared from woods 

 or when an old orchard site is renovated. After a year or 2, 

 grasses and weeds are allowed to re-establish themselves between 

 the rows or the land is re- seeded. 



Cultivation under the trees can affect nutrient level because 

 it destroys the roots in the surface soil which is particularly 

 high in K and P. Grass and weed competition are reduced by 

 cultivation, thus soil moisture is conserved and N is more avail- 

 able because grass competes with the trees for N. 



Chemical Weed Control . Considerable attention has been given to 

 the effect of herbicides on nutrition. A number of workers have 

 reported that sub-lethal concentrations of simazine will increase 

 leaf N of apple trees. In contrast, in our field studies, no 

 differences in nutrient levels or in growth of apple trees could 

 be attributed to simazine. However, in greenhouse studies, we 

 found th'at low concentrations of soi 1 - incorporated simazine did 

 increase leaf N of Mcintosh apple trees grown in 30 lb. cans. We 

 believe the lack of a response under our field conditions is 

 because most of the simazine is adsorbed by the organic matter in 

 the upper 3 inches of the soil and not available to tree roots. 



The effects of herbicide strips on root growth and nutrient 

 uptake have recently received much attention in England and Europe 

 The studies at East Mailing Research Station show that apple trees 

 produce most of their roots in and obtain most of their mineral 

 nutrients from the soil of the herbicide strip. Root growth under 



