412 MANAGING ORCHARD SOILS AND FERTILIZING TREES 



into nitrates before it is used by the trees or other plants. 

 Various soil micro-organisms such as fungi, algae, and bacteria 

 carry on these changes in the soil. 



(£>) Consider the Different Soil-Management Systems 

 Which Might Be Used, Many different systems of soil man- 

 agement have been and are being used in different orchards 

 of this country. Some of these are: 



(1) Sod culture — grass not cut. 



(2) Sod culture — ^grass cut and removed, or pastured. 



(3) Sod mulch — grass or legume cut and raked under limbs of 

 young trees, not raked up in old orchard. 



(4) Sod mulch plus additional mulch. 



(5) Clean cultivation and intercrops while the trees are young. 



(6) Clean cultivation, strip cultivation, and alternate-row 

 -cultivation. 



(7) Clean cultivation and cover crops. 



It will be seen that the different systems of soil culture fall into . 

 two large, general groups: sod versus tillage. In general, the 

 nitrate content of the soil is found to be much less under a 

 system of sod culture than where a system of clean cultivation 

 and cover crops is used, and orchards in sod usually respond 

 well to applications of a quickly available nitrogen fertilizer. 

 In addition to the fact that the grass itself uses nitrates, it 

 has been found that nitrification is much slower and less ex- 

 tensive under sod than in cultivated soil. Likewise the amount 

 of soil moisture is usually less in the sod orchard, unless a 

 heavy enough sod is produced so that an efficient mulch results 

 when the grass is cut and left upon the ground. Under that 

 procedure the moisture content of the soil appears to be about 

 the same in the sod and cultivated orchard during most of 

 the year, especially in the deeper and richer soils. Additional 

 3iiulching material, such as straw or hay, added to the cut grass 

 -will usually insure a soil moisture content equal to that of the 

 .cultivated orchard, even under soil conditions unfavorable 

 ior a good growth of grass or permanent legume. The danger 



