Field experiments were conducted in 2000 and 2001 in Meridian, Calif. to evaluate the effects of cover crop mixtures and reduced tillage on yield, soil nitrogen (N), weed growth, and soil moisture content in organic processing tomato (Lycopersicum esculentum) production. The trial was set up as a randomized complete-block design with eight treatments consisting of a 2 × 3 (cover crop × tillage) factorial design, a fallow control (F) and a single strip-till (ST) treatment. Cover crop mixtures were either legumes (L), common vetch (Vicia sativa), field pea (Pisum sativum) and bell bean (Vicia faba), or those legumes with grasses (GL), annual ryegrass/triticale (Lolium multiflorum/xTriticosecale) in 2000; cereal rye (Secale cereale)/triticale in 2001. Tillage treatments included an incorporation of the cover crop at planting (IP), a delayed incorporation (DI) (17 to 19 days after planting), and no-till (NT). Due to regrowth of the annual ryegrass in 2000, tomato fruit yields in 2000 were reduced by 50% to 97% within all GL treatments. However, regrowth of the cover crop was not a problem in 2001 and yields were not different among treatments. Total percent weed cover was 1.6 to 12.5 times higher in NT than IP treatments in 2000 and 2.4 to 7.4 times higher in 2001 as weed pressure was mainly affected by tillage practices and less by cover crop type. In 2000, available soil N was 1.7 to 9.4 times higher in L than GL treatments and was significantly influenced by tillage, but there were no treatment effects in 2001 due to a 60% reduction in weed pressure and minimal or no cover crop regrowth. Soil moisture content did not differ between treatments in either year. These results demonstrate the importance of appropriate selection and termination of cover crops for their successful adoption in organic conservation tillage systems.

No-till processing tomato (Lycopersicum esculentum Mill.) production in four winter cover crop-derived mulches was evaluated in 1997 and 1998 in Five Points, Calif. The effectiveness of two medics, `Sava' snail medic (Medicago scutellata Mill.) (sava), and `Sephi' barrel medic (Medicago truncatula Gaertn.) (sephi), and two cereal/legume cover crop mixtures, triticale/`Lana' woolypod vetch (X Triticosecale Wittm./Vicia dasycarpa Ten.) (triticale/vetch) and rye/`Lana' woolypod vetch (Secale cereale L./V. dasycarpa) (rye/vetch), was compared with two conventionally tilled fallow controls (with and without herbicide) (fallow+h and fallow-h) in suppressing weeds and maintaining yields with reduced fertilizer inputs. The comparison was conducted as a split plot, with three N fertilization rates (0, 100, and 200 lb/acre; 0, 112, and 224 kg·ha-1) as main plots and cover crops and fallow controls as subplots. Tomato seedlings were transplanted 3 weeks after the cover crops had been mowed and sprayed with herbicide. There were no significant differences in weed cover in the no-till cover crop treatments relative to the fallow controls in 1997. Early season weed suppression in rye/vetch and triticale/vetch plots was similar to herbicide-treated fallow (fallow+h) in 1998, however, later in the 1998 season weed suppression was best in the fallow+h. Tissue N was highest in the fallow treatments in both 1997 and 1998. Yields were highest in the triticale/vetch and fallow and lowest in sephi treatments in 1997, but there were no differences among treatments in 1998. These results demonstrate the feasibility of no-till mulch production of furrow irrigated processing tomatoes and identify opportunities for further optimization of the system.

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Digestate is a nutrient-rich fertilizer and appropriate techniques are required for its application during the maize season to reduce losses and increase the nitrogen use efficiency (NUE). The performance of two different fertigation techniques (drip irrigation and pivot) were assessed using the digestate liquid fraction. A two-year field test was carried out at two different sites in Lombardy, northern Italy. At each site, fertigation with pivot (P-F, site 1) or drip (D-F, site 2) systems was compared to reference fields where the same irrigation techniques without addition of digestate were used. During the two seasons, the performance of the fertigation systems, amount of fertilizers used, soil nitrogen content, yields, and nitrogen content of the harvested plants were monitored. The digestate application averaged 5 m3/ha per fertigation event with P-F and 4.9 m3/ha with D-F corresponding, respectively, to 28 and 23 kg N/ha. Both irrigation systems were suitable for fertigation provided that the digestate was adequately filtrated. Our results suggest that fertigation with digestate, if properly managed, can be applied during the growing season up to the full amount of nitrogen required by the crop.

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