ACCUMULATION AND DISTRIBUTION OF NITRATE–NITROGEN AND EXTRACTABLE PHOSPHORUS IN THE SOIL PROFILE UNDER VARIOUS ALTERNATIVE CROPPING SYSTEMS

ABSTRACT

Cropping systems can influence the accumulation and distribution of plant nutrients in the soil profile, which can affect their utilization efficiency by crops and pollution potential in the environment. A field experiment was conducted on a Dark Brown loam soil at Scott, Saskatchewan, Canada to assess the effects of input level, cropping diversity and crop phase on the accumulation and distribution of nitrate–nitrogen (N) and extractable phosphorus (P) in the soil profile at the end of 1995 to 2000 growing seasons. The 54 treatments were combinations of three input levels (organic—ORG, reduced—RED and high—HIGH), three cropping diversities (low diversity—LOW, diversified annual grains—DAG, and diversified annual and perennials—DAP), and six crop phases chosen from fallow (tillage-fallow or chem-fallow), green manure [lentil—Lens culinaris Medicus or sweet clover—Melilotus officinalis (L.) Lam], spring wheat (Triticum aestivum L.), canola (Brassica napus L. and Brassica rapa L.), fall rye (Secale cereale L.), field pea (Pisum sativum L.), spring barley (Hordeum vulgare L.), flax (Linum usitatissimum L.), oats (Avena sativa L.), and bromegrass (Bromus inermis Leyss), alfalfa (Medicago sativa Leyss) mixture hay. Soil was sampled from the 0–15, 15–30, 30–60, and 60–90 cm depths in each crop phase from 1995 to 2000, with additional depths 90–120, 120–150, 150–180, 180–210, and 210–240 cm taken from the wheat phase in 2000. In general, there were greater amounts of nitrate–N with HIGH input compared to ORG or RED inputs, especially under LOW diversity. The nitrate–N in various soil depths suggested some downward movement of nitrate–N to the deeper soil depths when HIGH input was compared to ORG input. In LOW cropping diversity, green manure or fallow usually had more nitrate–N in soil than other crop phases. In DAG and DAP cropping diversities, nitrate–N varied with crops and on average it had maximum concentration after wheat or canola in DAG and after hay followed closely by wheat in DAP. The ORG input level had greater nitrate–N than RED or HIGH inputs in some instances, most likely due to relatively low extractable P in soil for optimum crop growth under ORG input. Extractable P in the 0–15 and 15–30 cm soil depths tended to be greater under HIGH or RED inputs compared to the ORG input level in many cases. In summary, there was no consistent effect of cropping diversity on extractable P in soil under ORG input, but LOW diversity tended to show more extractable P compared to DAG and DAP diversities in some cases of RED and HIGH inputs. The green manure/fallow, HIGH input and LOW diversity treatments tended to result in higher nitrate–N and extractable P levels compared to the corresponding treatments, and the effects were more pronounced on nitrate–N than extractable P and in shallow compared to deeper soil layers.

ACKNOWLEDGMENTS

The authors thank Saskatchewan Agriculture and Food, Agriculture Development Fund and The Canada—Saskatchewan Green Plan for financial assistance, and L. Sproule, D. Gerein, and D. Leach for technical assistance.