Assessment of best management practices for nutrient cycling: A case study on an organic farm in a Mediterranean-type climate

Published source details Smukler S.M., O'Geen A.T. & Jackson L.E. (2012) Assessment of best management practices for nutrient cycling: A case study on an organic farm in a Mediterranean-type climate. Journal of Soil and Water Conservation (SWCS), 67, 16-31.
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This study is summarised as evidence for the following.

	Action	Category
	Pest regulation: Grow cover crops in arable fields Action Link
	Water: Grow cover crops in arable fields Action Link
	Crop production: Grow cover crops in arable fields Action Link
	Soil: Grow cover crops in arable fields Action Link

Pest regulation: Grow cover crops in arable fields

A controlled study in 2005–2006 in an irrigated tomato field in the Sacramento Valley, California, USA, found no differences in crop damage or weed biomass between the parts of the field that were cover cropped or fallow over winter. Crop damage: Similar numbers of tomatoes were damaged by insects in each part of the field (5–11 Mg fresh weight/ha), and similar numbers had blossom end rot (4 vs 2 Mg fresh weight/ha). Pest numbers: Similar amounts of weed biomass were found in each part of the field (2 Mg dry weight/ha). Methods: A field was divided into two parts: one part with a winter cover crop (mustard Brassica nigra, planted in autumn 2005, and disked into the soil in spring 2006), and one part fallow. Tomatoes were planted in both parts of the field in spring 2006. Tomatoes were sampled on 393 m transects (1 x 3 m quadrats every 30 m).
Water: Grow cover crops in arable fields

A controlled study in 2005–2006 in an irrigated tomato field in the Sacramento Valley, California, USA, found more phosphorus, but less ammonium, dissolved organic carbon, and sediment, in runoff from the part of the field that was cover cropped, compared to the part that was fallow. Water availability: Similar amounts of irrigation water were lost through discharge from each part of the field (42% vs 25%). Overall, less water was lost from the cover-cropped part, compared to the fallow part (44% less), and more water percolated deeply into the cover-cropped part (27% vs 15%), but it was not clear whether these differences were statistically significant. Nutrients: Similar amounts of nitrate were leached from each part of the field (measured in resin bags: 2.47 kg/ha). Higher phosphorus concentrations were found in runoff from the cover-cropped part of the field, compared to the fallow part, in one of two comparisons (in winter: 0.4 vs 0.2 mg dissolved reactive P/litre), but no differences were found in nitrogen or dissolved organic carbon concentrations (in winter: 0.1 mg NO₃-N/litre; 0.1 mg NH₄-N/litre; 5.8–7.4 mg C/litre; in summer: 1.6–2.2 mg NO₃-N/litre; 0.1–0.2 mg NH₄-N/litre; 3.3–3.9 mg C/litre). Lower loads (amounts/ha/irrigation or rainfall event) of ammonium and dissolved organic carbon were found in runoff from the cover-cropped part, compared to the fallow part (5.6 vs 8.3 g NH₄-N/ha/event; 0.3 vs 0.7 kg C/ha/event), but no differences were found in nitrate or phosphorus loads (in winter: 0.1 kg NO₃-N/ha/event; 20–22 g dissolved reactive P/ha/event; in summer: 0.4–0.9 kg NO₃-N/ha/event; 61–118 g dissolved reactive P/ha/event). Sediments: Less sediment was found in runoff from the cover-cropped part of a field, compared to the fallow part, in two of four comparisons (concentrations, in winter: 0.1 vs 0.7 g total suspended solids/litre; loads, in winter: 0.9 vs 5 kg/ha/event). Methods: A field was divided into two parts: one part with a winter cover crop (mustard Brassica nigra, planted in autumn 2005, and disked into the soil in spring 2006), and one part fallow. Tomatoes were planted in both parts of the field in spring 2006. Runoff water was collected in autosamplers (250 mL samples, every four hours, if there was >5 cm of water in the flow meter). Cumulative nitrate leaching from the soil was measured with anion exchange resin bags (buried at 75 cm depth).
Crop production: Grow cover crops in arable fields

A controlled study in 2005–2006 in an irrigated tomato field in the Sacramento Valley, California, USA, found some differences in tomato quality between the parts of the field that were cover cropped or fallow over winter. Crop yield: Similar tomato yields were found in each part of the field (55–67 Mg undamaged tomatoes/ha, fresh weight). Crop quality: More pink or split tomatoes were found in the cover-cropped part, compared to the fallow part (pink: 13 vs 11 Mg/ha; split: 6.8 vs 6.5), but similar numbers of green (22 vs 15 Mg/ha), sunburned (19 vs 20 Mg/ha), and mouldy or rotten (36 vs 27 Mg/ha) tomatoes were found in each part of the field (fresh weights). Methods: A field was divided into two parts: one part with a winter cover crop (mustard Brassica nigra, planted in autumn 2005, and disked into the soil in spring 2006), and one part fallow. Tomatoes were planted in both parts of the field in spring 2006. Tomatoes were sampled on 393 m transects (1 x 3 m quadrats every 30 m).
Soil: Grow cover crops in arable fields

A controlled study in 2005–2006 in an irrigated tomato field in the Sacramento Valley, California, USA, found less erosion of the part of the field that was cover cropped, compared to the part that was fallow. Soil erosion and aggregation: Less sediment was lost in runoff from the cover-cropped part, compared to the fallow part, in two of four comparisons (concentrations, in winter: 0.1 vs 0.7 g total suspended solids/litre; loads, in winter: 0.9 vs 5 kg/ha/rainfall event). Greenhouse gases: Similar amounts of greenhouse gas were emitted from each part of the field (<5 g N₂O-N/ha/day; 35–440 mg CO₂-C/m²/hour). Methods: A field was divided into two parts: one part with a winter cover crop (mustard Brassica nigra, planted in autumn 2005, and disked into the soil in spring 2006), and one part fallow. Greenhouse gases were measured one day/month (in chambers) in randomly located 16 m² plots (three plots in each part of the field). Runoff water was collected in autosamplers (250 mL samples, every four hours, if there was >5 cm of water in the flow meter).