The experiments occurred at the USDA-ARS organic research
farm in Salinas, CA (lat. 36.622658, long. -121.549172, elevation
37 m), where the soil is a Chualar loamy sand (fine-loamy, mixed,
superactive, thermic Typic Argixerol). The site has been certified
organic since 1999, and inputs described were allowable under
the USDA National Organic Program. The experiment occurred in
a 48 by 15 m area on the east side of a 0.9 ha field that has been
in a long-term commercial-scale trial
with an annual rotation of romaine lettuce (May–June), broccoli
(July–October), and winter cover crops of legume cereal mixtures
(October–March), since 2003. Romaine lettuce is here after referred
to as lettuce. Cover crops were mowed and incorporated
into the soil with a spader on 19 February 2008 and 13 March
2009. After a decomposition period, a tractor with lister plows
was used to form peaked beds (101.6 cm wide) on 7 April 2008
and 17 April 2009. Urban yard waste compost (C:N 22) was
broadcast at approximately 7.6 Mg per ha (oven dry basis) onto
the beds and incorporated with a rolling cultivator. Pelleted organic
fertilizer of chicken manure and feather meal (8N-1P-1K) was injected
at 58 and 66 kg N per ha with a fertilizer applicator in two
The experiments occurred at the USDA-ARS organic researchfarm in Salinas, CA (lat. 36.622658, long. -121.549172, elevation37 m), where the soil is a Chualar loamy sand (fine-loamy, mixed,superactive, thermic Typic Argixerol). The site has been certifiedorganic since 1999, and inputs described were allowable underthe USDA National Organic Program. The experiment occurred ina 48 by 15 m area on the east side of a 0.9 ha field that has beenin a long-term commercial-scale trial with an annual rotation of romaine lettuce (May–June), broccoli(July–October), and winter cover crops of legume cereal mixtures(October–March), since 2003. Romaine lettuce is here after referredto as lettuce. Cover crops were mowed and incorporatedinto the soil with a spader on 19 February 2008 and 13 March2009. After a decomposition period, a tractor with lister plowswas used to form peaked beds (101.6 cm wide) on 7 April 2008and 17 April 2009. Urban yard waste compost (C:N 22) wasbroadcast at approximately 7.6 Mg per ha (oven dry basis) ontothe beds and incorporated with a rolling cultivator. Pelleted organicfertilizer of chicken manure and feather meal (8N-1P-1K) was injectedat 58 and 66 kg N per ha with a fertilizer applicator in two
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