Residual effects of poultry litter on silage maize (Zea mays L.) growth and soil properties derived from volcanic ash

Poultry litter (PL) is a cheap alternative to conventional fertilizers. The use of PL in this way also reduces the environmental problems normally associated with its disposal. The residual effect of PL may reduce the amount of fertilizer (especially N fertilizer) required by subsequent crops. This study examines the residual effects of PL (with and without additional mineral fertilizer) on the properties of a volcanic ash soil and on silage maize (Zea mays) yields in central Chile. Poultry litter and mineral fertilizer were applied in 20022003 and their residual effects were determined in 2004-2006. The dry matter (DM) yield, nutrient balance and apparent nitrogen recovery efficiency (ANRE) of the silage maize were determined for each season, and the soil properties were analyzed at three depths (0-20, 20-40 and 40-60 cm) at the end of the third season. Crop yield showed a positive response to all fertilizer treatments. The residual effect, the nutrient balance, N uptake and ANRE also improved with fertilizer treatment, especially with the PL treatments. The average DM yield for the PL treatments was higher than that observed using mineral fertilizer by 2.8 and 1.2 Mg ha(-1) in the third and fourth years, respectively. The ANRE was generally higher in the PL treatments, although it decreased over time (12.4 and 1.7% for the last 2 years, respectively). The mean ANREs for the mineral fertilizer treatment were 4.1 and 1.6% for the same years. The results suggest that the PL treatments had an important positive residual effect in terms of N supply. This should be taken into account when planning the next crop. After two annual applications of PL, slight increases were observed in soil NO3-N at a depth of 0-20 cm, and extractable P at depths of 20-40 cm and 40-60 cm. No other soil variables were significantly affected by any of the treatments. An additional source of K was found to be necessary to maintain an adequate soil K level.