Soil-plant nitrogen dynamics following incorporation of a mature rye cover crop in a lettuce production system

Published source details Wyland L.J., Jackson L.E. & Schulbach K.F. (1995) Soil-plant nitrogen dynamics following incorporation of a mature rye cover crop in a lettuce production system. The Journal of Agricultural Science, 124, 17-25.
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This study is summarised as evidence for the following.

	Action	Category
	Grow cover crops when the field is empty Action Link
	Amend the soil with fresh plant material or crop remains Action Link
	Soil: Grow cover crops in arable fields Action Link
	Water: Grow cover crops in arable fields Action Link

Grow cover crops when the field is empty

A controlled, randomized, replicated experiment in 1991-1992 on fine loam in California, USA (Wyland et al. 1995) found reduced soil nitrate under cover-cropped (4.3 g nitrate/m²) compared to bare soil (8.6 g nitrate/m²), prior to rye Secale cereale incorporation. Available nitrogen was also higher under cover-cropped (1.8 g N/m²) compared to bare soil (1.1 g N/m²). There were two winter treatments: a rye Secale cereale crop sown in December then incorporated into the soil after16 weeks using a disc plough, and bare-fallow. Both treatments received the same tillage treatment (regular passes with a disc plough). Plots were 8 x 4 m. There were three replicates. Soil was sampled prior to rye incorporation (60 cm depth).
Amend the soil with fresh plant material or crop remains

A controlled, randomized, replicated experiment in 1991-1992 on fine loam in California, USA (Wyland et al. 1995) found higher microbial biomass and available nitrogen in soil with rye Secale cereal incorporated (23 and 35 μg N/g dry soil), compared to bare soil (10 and 20 μg N/g respectively), after three passes with a disc plough. There were two winter treatments: a rye Secale cereale crop sown in December then incorporated into the soil after16 weeks using a disc plough, and bare-fallow. Both treatments received the same tillage treatment (regular passes with a disc plough). Plots were 8 x 4 m. There were three replicates. Soil was sampled prior to rye incorporation (60 cm depth).
Soil: Grow cover crops in arable fields

A replicated, randomized, controlled study in 1991–1992 in an irrigated lettuce field in the Salinas Valley, California, USA, found less nitrate, but more ammonium, mineralizable nitrogen, and microbial biomass, in soils with winter cover crops, compared to bare soils. Nutrients: Less nitrate, more ammonium, and more mineralizable nitrogen were found in soils with winter cover crops, compared to bare soils, before the cover crops were incorporated into the soil (4.3 vs 8.6 g NO₃-N/m², 0–60 cm depth; 1.8 vs 1.1 g NH₄-N/m², net mineralizable nitrogen, 0–30 cm depth; 0.26 vs 0.24 g NH₄-N/m², 0–60 cm depth), and also in some comparisons after the cover crops were incorporated (1–6 vs 3–24 µg NO₃-N/g dry soil, 0–15 cm depth; 3–38 vs 1–21 µg NH₄-N/g dry soil, net mineralizable nitrogen, 0–15 cm depth; 0.17–0.98 vs 0.10–0.68 µg NH₄-N/g dry soil; 1–15 cm depth; number of significantly different comparisons not clearly reported). Soil organisms: More microbial biomass (measured as nitrogen) was found in soils with winter cover crops, compared to bare soils, in some comparisons (14–29 vs 6–14 µg N/g dry soil). Methods: Three plots had winter cover crops (Merced rye Secale cereale, sown on 19 December 1991) and three plots had bare soils over winter. The plots (raised beds) were 8 x 4 m each. All plots were disked on 8 April (incorporating the cover crops). Soil samples were collected 6 days before the cover crops were incorporated, and on 7–9 days between cover-crop incorporation and lettuce harvesting. Lettuce was sown on 8 May and harvested on 8 July 1992.
Water: Grow cover crops in arable fields

A replicated, randomized, controlled study in 1991–1992 in an irrigated lettuce field in the Salinas Valley, California, USA, found less water in soils with winter cover crops, compared to bare soils. Water availability: Less water was found in soils with cover crops, compared to bare soils, in some comparisons (7 and 12 days after cover crops were incorporated into the soil: 7–9% vs 9–11% water; total number of significantly different comparisons not clearly reported). Methods: Three plots had winter cover crops (Merced rye Secale cereale, sown on 19 December 1991) and three plots had bare soils over winter. The plots (raised beds) were 8 x 4 m each. All plots were disked on 8 April (incorporating the cover crops). Soil samples were collected on 7–9 days between cover-crop incorporation and lettuce harvesting. Lettuce was sown on 8 May and harvested on 8 July 1992.