Ground covers and fertigation in IP apple orchards .3. Biomass yield and nutrient uptake of the ground covers and influence on soil moisture and nutrients in the soil

In a two-factor field trial on an Alfisol derived from loess the influence of soil management and fertilizing on the chemical and physical properties of the soil olf an apple orchard ('Elstar'/M9) were investigated under Northwest German climatic conditions. The use of herbicide on the tree strips was compared with cultivation and three different cover crops, ground ivy (Glechoma hederacea), a grass mixture, and clover (Trifolium repens). The different tree strip treatments were combined with fertigation or broadcast fertilizer application plus irrigation. Besides chemical and physical properties of the soil also the annual herbage dry-matter yield and the amount of nutrient uptake by the cover crops were investigated. The highest nutrient uptake (N, P, K, Mg, Ca) was caused by the ''Grass Cover'', followed by ''Clover'' and ''Ground Ivy''. There were only minor differences in the phosphorus and potassium contents in the top soil layer (0-30 cm): ''Herbicide'' treatment resulted in slightly higher P and K content. There was no significant difference in the magnesium content of the soil. On the other hand, the fertilizing method did not influence the nutritional status of the soil. Compared to the other tree strip treatments ''cultivation'' resulted in a depletion of total nitrogen in the soil. No effects on soil-pH (top soil) were observed. Soil moisture tension was influenced by the tree strip treatments down to a depth of 90 cm. The highest soil moisture tension was found in the ''Clover'' treatment. Soil moisture under ''Ground Ivy'' and ''Grass'' was in an intermediate position between ''Clover'' and bare soil. Tree strips which were kept weed-free, no matter whether by use of herbicide or cultivation, usually had the lowest soil moisture tension. Compared to herbicide application a water-preserving effect through moderate cultivation was not observed.