Long-term Tillage and Nitrogen Fertilization Effects on Soil Properties and Crop Yields

The impact of agricultural intensification on soil degradation now is occurring in tropical countries. The objective of this study was to determine the effect of long-term tillage and N fertilization on soil properties and crop yields in corn-soybean rotation. This long-term study which initiated since 1987 was carried out on a Typic Fragiudult soil at Politeknik Negeri Lampung, Sumatra (105o13’45.5"-105o13’48.0"E, 05o21’19.6"-05o21’19.7"S) in 2010 and 2011. A factorial experiment was arranged in a randomized block design with four replications. The first factor was tillage system namely intensive tillage (IT) and conservation tillage (CT) which consisted of minimum tillage (MT) and no-tillage (NT); while the second factor was N fertilization with rates of 0, 100 and 200 kg N ha-1 applied for corn, and 0, 25, and 50 kg N ha-1 for soybean. The results showed that bulk density and soil strength at upper layer after 24 years of cropping were similar among treatments, but the soil strength under IT at 50-60 cm depth was 28.2% higher (p<0.05) than NT. Soil moisture and temperature under CT at 0-5 cm depth were respectively 38.1% and 4.5% higher (p<0.05) than IT. High N rate decreased soil pH at 0-20 cm depth as much as 10%, but increased total soil N at 0-5 cm depth as much as 19% (p<0.05). At 0-10 cm depth, MT with no N had highest exchangeable K, while IT with medium N rate had the lowest (p<0.05). At 0-5 cm depth, MT with no N had highest exchangeable Ca, but it had the lowest (p<0.05) if combined with higher N rate. Microbial biomass C throughout the growing season for NT was consistently highest and it was 14.4% higher (p<0.05) than IT. Compared to IT, Ap horizon of CT after 24 years of cropping was deeper, with larger soil structure and more abundance macro pores. Soybean and corn yields for long-term CT were 64.3% and 31.8% higher (p<0.05) than IT, respectively. Corn yield for long-term N with rate of 100 kg N ha-1 was 36.4% higher (p<0.05) than without N.