On-farm assessment of organic matter and tillage management on vegetable yield, soil, weeds, pests, and economics in California

Pest regulation: Add compost to the soil

A replicated, randomized, controlled study in 1998–2000 in farmland in the Salinas Valley, California, USA, found no differences in most crop diseases or crop pests, in plots with or without added compost. Pest numbers: Less corky root disease was found in plots with added compost, compared to plots without it, in one of six comparisons (2.2 vs 2.9 disease severity, on a scale from 1 to 12, on which 12 is the highest severity). Similar amounts of Sclerotina minor disease, big vein disease, or pea leafminers Liriomyza huidobrensis were found in plots with and without added compost (S. minor: 0.3–1.9% vs 0.3–1.8% of plants had symptoms; big vein: 3.0–3.6% vs 2.7–3.4% of plants had symptoms; leafminers: 10–81 vs 8–98 insects/sticky card). Methods: There were four plots (0.52 ha), for each of four treatments (minimum tillage or conventional tillage, with or without added organic matter). In plots with added organic matter, compost was added two times/year, and a cover crop (Merced rye) was grown every autumn or winter. The compost was made from municipal yard waste, salad packing plant waste, horse manure, clay, straw, and other compost. Lettuce or broccoli crops were grown in raised beds. Soils were disturbed to different depths (conventional tillage: 50 cm with disking, cultivating with a liliston, sub-soiling, bed re-making, and bed-shaping; minimum tillage: 20 cm with a liliston, rollers, and bed-shaping). It was not clear whether these results were a direct effect of adding compost or growing cover crops.

Water: Use reduced tillage in arable fields

A replicated, randomized, controlled study in 1998–2000 in an irrigated vegetable field in the Salinas Valley, California, USA, found less water in soils with reduced tillage, compared to conventional tillage. Water availability: Less water was found in soils with reduced tillage, compared to conventional tillage, in 12 of 16 comparisons (0.07–0.26 vs 0.08–0.27 g water/g soil; 0–15 cm depth). Methods: There were four plots (0.52 ha), for each of four treatments (reduced tillage or conventional tillage, with or without added organic matter). In plots with added organic matter, compost was added two times/year, and a cover crop (Merced rye) was grown every autumn or winter. Lettuce or broccoli crops were grown in raised beds. Sprinklers and drip irrigation were used in all plots. Soils were disturbed to different depths (conventional tillage: disking to 50 cm depth, cultivating, sub-soiling, bed re-making, and bed-shaping; reduced tillage: cultivating to 20 cm depth, rolling, and bed-shaping). Soils were collected, along the planting line, with 6 cm soil cores.

Crop production: Add compost to the soil

Soil: Use reduced tillage in arable fields

A replicated, randomized, controlled study in 1998–2000 in an irrigated vegetable field in the Salinas Valley, California, USA, found more microbial biomass in soils with reduced tillage, compared to conventional tillage. Tillage had inconsistent effects on nutrients. Nutrients: Similar amounts of nitrogen were found in soils with reduced tillage, compared to conventional tillage (1.5–1.6 g total N/kg soil; 0–15 cm depth). At depths of 0–90 cm, less nitrate was found in soils with reduced tillage, compared to conventional tillage, in 12 of 14 comparisons (4–61 vs 5–64 g NO₃-N/g soil), but more nitrate was found in one of 14 comparisons (34 vs 29). At depths of 0–15 cm, tillage had inconsistent effects on nitrate (0–64 vs 0–53 μg NO₃-N/g soil) and ammonium (0–9 vs 0–6 μg NH₄-N/g soil). Soil organisms: More microbial biomass (measured as carbon) was found in soils with reduced tillage, compared to conventional tillage, in two of 16 comparisons (120–130 vs 90–100 μg C/g soil). More microbial biomass (measured as nitrogen) was found in soils with reduced tillage, compared to conventional tillage, in three of 16 comparisons (12–15 vs 5–8 μg N/g soil). Methods: There were four plots (0.52 ha), for each of four treatments (reduced tillage or conventional tillage, with or without added organic matter). In plots with added organic matter, compost was added two times/year, and a cover crop (Merced rye) was grown every autumn or winter. Lettuce or broccoli crops were grown in raised beds. Sprinklers and drip irrigation were used in all plots. Soils were disturbed to different depths (conventional tillage: disking to 50 cm depth, cultivating, sub-soiling, bed re-making, and bed-shaping; reduced tillage: cultivating to 20 cm depth, rolling, and bed-shaping). Soils were collected, along the planting line, with 6 cm soil cores.

Pest regulation: Use reduced tillage in arable fields

A replicated, randomized, controlled study in 1998–2000 in an irrigated vegetable field in the Salinas Valley, California, USA, found similar numbers of crop pests and diseases in plots with reduced tillage, compared to conventional tillage. Pest numbers: Similar numbers of crop pests and diseases were found in plots with reduced tillage, compared to conventional tillage (Sclerotina minor: 0.3–1.8 vs 0.3–1.9% of plants had symptoms; big vein disease: 3.0–3.4 vs 2.7–3.6% of plants had symptoms; pea leafminers: 10–98 vs 8–84 insects/sticky card; 2.2–3.4 vs 2.2–3.6% corky root disease severity, on a scale from 1 to 12, on which 12 is the highest severity). Methods: There were four plots (0.52 ha), for each of four treatments (reduced tillage or conventional tillage, with or without added organic matter). In plots with added organic matter, compost was added two times/year, and a cover crop (Merced rye) was grown every autumn or winter. Lettuce or broccoli crops were grown in raised beds. Sprinklers and drip irrigation were used in all plots. Soils were disturbed to different depths (conventional tillage: disking to 50 cm depth, cultivating, sub-soiling, bed re-making, and bed-shaping; reduced tillage: cultivating to 20 cm depth, rolling, and bed-shaping).

Crop production: Use reduced tillage in arable fields

A replicated, randomized, controlled study in 1998–2000 in an irrigated vegetable field in the Salinas Valley, California, USA, found that tillage had inconsistent effects on crop yield and quality. Crop yield: Lower broccoli yields were found in plots with reduced tillage, compared to conventional tillage (610–620 vs 630–640 g dry weight/m²). Higher lettuce yields were found in plots with reduced tillage, compared to conventional tillage, in two of six comparisons (310–410 vs 300–390 g dry weight/m²), but lower lettuce yields were found in two of six comparisons (280–390 vs 300–430). Crop quality: Smaller lettuce or broccoli plants were found in plots with reduced tillage, compared to conventional tillage, in five of eight comparisons (lettuce: 750–1,080 vs 830–1,150 g fresh weight/plant; broccoli: 240 vs 270), but larger plants were found in two of eight comparisons (lettuce: 1,090 vs 1,050; broccoli: 230 vs 210). Methods: There were four plots (0.52 ha), for each of four treatments (reduced tillage or conventional tillage, with or without added organic matter). In plots with added organic matter, compost was added two times/year, and a cover crop (Merced rye) was grown every autumn or winter. Lettuce or broccoli crops were grown in raised beds. Sprinklers and drip irrigation were used in all plots. Soils were disturbed to different depths (conventional tillage: disking to 50 cm depth, cultivating, sub-soiling, bed re-making, and bed-shaping; reduced tillage: cultivating to 20 cm depth, rolling, and bed-shaping). Crops were collected in two 2 m² areas/plot.

Water: Add compost to the soil

A replicated, randomized, controlled study in 1998–2000 in an irrigated vegetable field in the Salinas Valley, California, USA, found more water in soils with added compost, compared to soils without added compost, in six of 16 comparisons. Water availability: More water was found in soils with added compost, compared to soils without added compost, in six of 16 comparisons (0.10–0.27 vs 0.07–0.26 g water/g soil, 0–15 cm depth). Methods: There were four plots (0.52 ha), for each of four treatments (minimum tillage or conventional tillage, with or without added organic matter). In plots with added organic matter, compost was added two times/year, and a cover crop (Merced rye) was grown every autumn or winter. The compost was made from municipal yard waste, salad packing plant waste, horse manure, clay, straw, and other compost. Lettuce or broccoli crops were grown in raised beds. Sprinklers and drip irrigation were used in all plots. Soils were disturbed to different depths (conventional tillage: 50 cm with disking, cultivating with a liliston, sub-soiling, bed re-making, and bed-shaping; minimum tillage: 20 cm with a liliston, rollers, and bed-shaping). Soils were collected, along the planting line, with 6 cm soil cores. It was not clear whether these results were a direct effect of adding compost or growing cover crops.

Soil: Add compost to the soil

A replicated, randomized, controlled study in 1998–2000 in an irrigated vegetable field in the Salinas Valley, California, USA, found more organic matter, and sometimes found more microbial biomass, in soils with added compost, compared to soils without added compost. Adding compost had inconsistent effects on nutrients. Organic matter: More carbon was found in soils with added compost, compared to soils without added compost (15 vs 14 g total C/kg soil, 0–15 cm depth). Nutrients: More nitrogen was found in soils with added compost, compared to soils without added compost (1.6 vs 1.5 g total N/kg soil, 0–15 cm depth). At depths of 0–90 cm, less nitrate was found in soils with added compost, compared to soils without added compost, in 13 of 14 comparisons (4–54 vs 5–64 g NO₃-N/g soil), but more nitrate was found in one of 14 comparisons (34 vs 24). At depths of 0–15 cm, less nitrate was found in soils with added compost, compared to soils without added compost, in six of 16 comparisons (2–17 vs 3–64 μg NO₃-N/g soil), but more nitrate was found in one of 16 comparisons (31 vs 12). At depths of 0–15 cm, less ammonium was found in soils with added compost, compared to soils without added compost, in eight of 16 comparisons (1–6 vs 5–9 μg NH₄-N/g soil), but more ammonium was found in two of 16 comparisons (4–7 vs 1–4). Soil organisms: More microbial biomass (measured as carbon) was found in soils with added compost, compared to soils without added compost, nine of 16 comparisons (120–220 vs 80–130 μg C/g soil). More microbial biomass (measured as nitrogen) was found in soils with added compost, compared to soils without added compost, in 10 of 16 comparisons (14–26 vs 5–17 μg N/g soil). Methods: There were four plots (0.52 ha), for each of four treatments (minimum tillage or conventional tillage, with or without added organic matter). In plots with added organic matter, compost was added two times/year, and a cover crop (Merced rye) was grown every autumn or winter. The compost was made from municipal yard waste, salad packing plant waste, horse manure, clay, straw, and other compost. Lettuce or broccoli crops were grown in raised beds. Sprinklers and drip irrigation were used in all plots. Soils were disturbed to different depths (conventional tillage: 50 cm with disking, cultivating with a liliston, sub-soiling, bed re-making, and bed-shaping; minimum tillage: 20 cm with a liliston, rollers, and bed-shaping). Soils were collected, along the planting line, with 6 cm soil cores. It was not clear whether these results were a direct effect of adding compost or growing cover crops.

Crop production: Grow cover crops in arable fields

A replicated, randomized, controlled study in 1998–2000 in an irrigated vegetable field in the Salinas Valley, California, USA, found lower lettuce yields in plots with winter cover crops, compared to plots without cover crops, but cover crops had inconsistent effects on crop quality. Crop yield: Lower lettuce yields were found in plots with cover crops, in one of four comparisons (281 vs 313 g dry weight/m²). No differences in broccoli yields were found in plots with or without cover crops (625–644 vs 606–633 g dry weight/m²). Crop quality: Larger lettuces were found in plots with cover crops, in two of four comparisons (1,080–1,140 vs 1,030–1,100 g fresh weight/plant), but smaller lettuces were found in one of four comparisons (750 vs 790). Larger broccoli plants were found in plots with cover crops (240–270 vs 210–220 g fresh weight/plant). Methods: There were four plots (0.52 ha), for each of four treatments (reduced tillage or conventional tillage, with or without added organic matter). In plots with added organic matter, compost was added two times/year, and a cover crop (Secale cereale Merced rye) was grown every autumn or winter. Lettuce or broccoli crops were grown on raised beds. Sprinklers and drip irrigation were used in all plots. Soils were disturbed to different depths (conventional tillage: disking to 50 cm depth, cultivating, sub-soiling, bed re-making, and bed-shaping; reduced tillage: cultivating to 20 cm depth, rolling, and bed-shaping). Crops were collected in two 2 m² areas/plot. It was not clear whether these results were a direct effect of adding compost or growing cover crops.

Pest regulation: Grow cover crops in arable fields

A replicated, randomized, controlled study in 1998–2000 in an irrigated vegetable field in the Salinas Valley, California, USA, found less corky root disease in plots with winter cover crops, compared to plots without cover crops. Crop damage: Less corky root disease was found in plots with cover crops, in one of four comparisons (2.2 vs 2.9 disease severity, on a scale from 1 to 12, on which 12 is the highest severity). Similar amounts of Sclerotina minor disease and big vein disease were found in plots with or without cover crops (S. minor: 0.3–1.9 vs 0.3–1.7% of plants had symptoms; big vein: 3.0–3.6 vs 2.7–3.4% of plants had symptoms). Pest numbers: Similar numbers of Liriomyza huidobrensis pea leafminers were found in plots with or without cover crops (10–81 vs 8–98 insects/sticky card). Methods: There were four plots (0.52 ha), for each of four treatments (reduced tillage or conventional tillage, with or without added organic matter). In plots with added organic matter, compost was added two times/year, and a cover crop (Secale cereale Merced rye) was grown every autumn or winter. Lettuce or broccoli crops were grown on raised beds. Sprinklers and drip irrigation were used in all plots. Soils were disturbed to different depths (conventional tillage: disking to 50 cm depth, cultivating, sub-soiling, bed re-making, and bed-shaping; reduced tillage: cultivating to 20 cm depth, rolling, and bed-shaping). It was not clear whether these results were a direct effect of adding compost or growing cover crops.

Soil: Grow cover crops in arable fields

A replicated, randomized, controlled study in 1998–2000 in an irrigated vegetable field in the Salinas Valley, California, USA, found more organic matter, more microbial biomass, less nitrate, and/or less ammonium in soils with winter cover crops, compared to soils without cover crops, in most comparisons. More ammonium was found in two of 12 comparisons. Organic matter: More carbon was found in soils with cover crops (15 vs 14 g total C/kg soil; 0–15 cm depth). Nutrients: More total nitrogen was found in soils with cover crops (1.6 vs 1.5 g total N/kg soil; 0–15 cm depth). At depths of 0–90 cm, less nitrate was found in soils with cover crops (4–54 vs 5–64 g NO₃–N/g soil), and less nitrate was also found at depths of 0–15 cm, in seven of 12 comparisons (2–18 vs 3–64 μg NO₃-N/g soil). At depths of 0–15 cm, less ammonium was found in soils with cover crops, in six of 12 comparisons (1–4 vs 5–7 μg NH₄–N/g soil), but more ammonium was found in two of 12 comparisons (4–7 vs 1–4). Soil organisms: More microbial biomass (measured as carbon) was found in soils with cover crops, in 10 of 12 comparisons (120–220 vs 80–130 μg C/g soil). More microbial biomass (measured as nitrogen) was found in soils with cover crops, in 11 of 12 comparisons (14–27 vs 5–17 μg N/g soil). Methods: There were four plots (0.52 ha), for each of four treatments (reduced tillage or conventional tillage, with or without added organic matter). In plots with added organic matter, compost was added two times/year, and a cover crop (Secale cereale Merced rye) was grown every autumn or winter. Lettuce or broccoli crops were grown on raised beds. Sprinklers and drip irrigation were used in all plots. Soils were disturbed to different depths (conventional tillage: disking to 50 cm depth, cultivating, sub-soiling, bed re-making, and bed-shaping; reduced tillage: cultivating to 20 cm depth, rolling, and bed-shaping). Soils were collected, along the planting line, with 6 cm soil cores. It was not clear whether these results were a direct effect of adding compost or growing cover crops.

Water: Grow cover crops in arable fields

A replicated, randomized, controlled study in 1998–2000 in an irrigated vegetable field in the Salinas Valley, California, USA, found more water in soils with cover crops, compared to soils without cover crops, in six of 12 comparisons. Water availability: More water was found in soils with cover crops, compared to soils without cover crops, in six of 12 comparisons (0.10–0.27 vs 0.07–0.26 g water/g soil; 0–15 cm depth). Methods: There were four plots (0.52 ha), for each of four treatments (reduced tillage or conventional tillage, with or without added organic matter). In plots with added organic matter, compost was added two times/year, and a cover crop (Merced rye) was grown every autumn or winter. Lettuce or broccoli were grown on raised beds. Sprinklers and drip irrigation were used in all plots. Soils were disturbed to different depths (conventional tillage: disking to 50 cm depth, cultivating, sub-soiling, bed re-making, and bed-shaping; reduced tillage: cultivating to 20 cm depth, rolling, and bed-shaping). Soils were collected, along the planting line, with 6 cm soil cores. It was not clear whether these results were a direct effect of adding compost or growing cover crops.