Soil Fertility improvement in Fruit Orchards by Windrowing Urban Plant Debris and Poultry Litter

When poultry litter (PL) overlain with shredded urban plant debris (UPD) was applied at low, medium and high rates during two growing seasons in a windrow or band on one side of newly planted citrus trees, tree growth at the lowest rate was similar to that of the medium and high rate, suggesting the lowest rate may be adequate. Applied nitrogen rates per treated acre for the PL/UPD treatments ranged from 1.2 to 3.8 times the conventional synthetic fertilizer rate and were from 1.8 to 5.2 times as expensive. Soil and leaf nutrient levels varied widely and were excessive in some cases. Soil moisture levels were not affected by different treatments. However treatment effects may be masked during these first two growing seasons by high tree nutrient levels at planting, residual soil nutrient levels in this previously planted citrus grove and the 3-4 year time frame required for applied high organic treatments such as these to affect soil characteristics and plant growth. An additional consideration is that PL/UPD treatments were not soil-incorporated by applied as a windrow on the soil surface to avoid damaging citrus roots near the surface. The high carbon::nitrogen ratios in the UPD (as high as 145:1) may also have affected PL nitrogen availability but will also ensure slow mineralization rates for plant nutrients. Vigorous root growth into the PL/UPD layers occurred and additional benefits for management of insect pests were also observed.