Previous Broiler Litter Fertilization Treatment Effects on Soybean.

In Kentucky, poultry production has grown tremendously in recent years.  To accommodate this growth, there is a need for environmentally conscious disposal sites for waste material.  One of the most promising areas for application is agricultural fields. A study was initiated in 1997 with annual broiler litter application treatments of 0, 2.2, 4.5, 6.7, 9.0, 11.2, 13.4, and 15.7 Mg/ha.  In 2003, broiler litter application was reduced to a half the above rate. In 2004, no broiler litter applications were made.  From 1997 to 2004, corn was grown with only broiler litter applications and no fertilizer.  Throughout 2005 and 2006 seasons, soybeans were grown on these plots with no further broiler litter applications.  For these soybean crops, extra P (258 kg/ha P₂O₅) and K (280 kg/ha K₂O) was applied to the plots that had received the low rates of broiler litter (2.2 and 4.5 Mg/ha).  In these two years, the soybeans receiving the extra supplemental P and K did not yield as well as the plots with higher broiler litter rates.  In 2007, a soybean experiment was conducted to investigate the reasons for this difference.  Because of a severe drought during 2007, the experiment was irrigated. At the R6 stage, the total above-ground portion of the plants was harvested and analyzed for 13 elements.  Unlike the previous two years, no significant yield differences between treatments were found.  No statistical differences were observed between treatments for soil bulk density and soil water holding capacity.  The drought had a large impact on the results. Differences were found between treatments for plant uptake of the following elements: P, K, Ca, Mg, S, Al, B, Cu, and Zn.  A significant correlation was found between Cu plant uptake and yield (r = 0.4437).  The relationship between Cu uptake and yield will require additional research.