Root distribution of field-grown crisphead lettuce (<i>Lactuca sativa</i>L.) under different fertilizer and mulch treatment

Abstract

Abstract We determined the seasonal changes in the root system of field-grown crisphead lettuce under different fertilizer treatment (stripe, broadcast, and no-nitrogen (absence of nitrogen)) and polyethylene film mulch treatment. Soil blocks less than 1 L volume were sampled from 1 quarter of a plant's rooting volume and roots were separated from the soil blocks by boiling. The root length was determined by the modified line intersect method. Root development in the broadcast plots was better in the 0–30 cm layer but worse below this depth compared to the no-nitrogen plot. In the stripe plots, the rooting pattern was similar to that in the broadcast plots in the 0–30 cm layer and similar to the no-nitrogen plot below that depth. Roots in the stripe plots showed characteristics of both broadcast and no-nitrogen application. With the mulch, the root length density was the highest in the 0–10 cm layer, while without mulch it was highest in the 10–20 cm layer. The root / shoot ratio for nitrogen absorption was ca. 10%. The 0–30 cm layer accounted for more than 80% of the total root length due to the abrupt increase in soil hardness below this depth. Total root length ranged from 1,021 to 1,931 m plant−1 at harvest (50 cm deep). The fine root length / weight ratio was 363 m g−1 dry root and the fine root diameter averaged 207 μm. Constraints on methodologies such as sampling depth, removal of debris, saving of labor, and core sampling were outlined.