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Gary R. Cline and Anthony F. Silvernail

A 4-year field experiment examined how monoculture and biculture winter cover crops were affected by prior inorganic nitrogen (N) fertilization of sweet corn (Zea mays) and by kill dates associated with tillage methods. Hairy vetch (Vicia villosa) biomass production and N content remained relatively constant with (N+) or without (N0) prior N application. In N+ treatments, biomass production of winter rye (Secale cereale) and a vetch-rye biculture were significantly greater than vetch biomass production. Rye responded to prior N fertilization and recovered N from residual inorganic N fertilizer at an average annual rate of 30 kg·ha-1 (27 lb/acre), excluding contributions of roots. Nitrogen contents of vetch and biculture cover crops were similar in most years and were significantly greater than those of rye. Nitrogen contents in vetch and biculture treatments were not increased by the residual inorganic N fertilizer addition of the N+ treatment. In the biculture treatment prior N application increased total biomass production but decreased the percentage of vetch biomass. Monoculture vetch biomass production was significantly increased by delaying cover crop kill dates for 8 days in mid-May. However, such delays also significantly lowered vetch foliar N concentrations and consequently did not significantly affect vetch N content. No significant effects of delays on rye or biculture cover crops were detected. It was concluded that prior fertilization of sweet corn with inorganic N affected various cover crops differently and that delaying vetch kill dates 8 days increased biomass production but did not affect N content.

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Gary R. Cline and Anthony F. Silvernail

Effects of tillage, inorganic N, and winter cover crops on sweet corn (Zea mays) were examined in 1994, 1995, and 1996. Tillage treatments were tillage or no tillage, and N treatments were the addition of inorganic N at 0 (N0) or 200 (N+) kg·ha-1 (0 or 179 lb/acre). Winter cover crops included hairy vetch (Vicia villosa), winter rye (Secale cereale), and a vetch/rye biculture. In the N0, rye treatment, the soil was N deficient in 1994 and highly N deficient in 1995 and 1996. When vetch shoot N content was ≥150 kg·ha-1 (134 lb/acre) (1994 and 1995), addition of inorganic N did not increase corn yields, and it only increased corn foliar N concentrations by 8%. Reductions in corn yields (29%) and foliar N concentrations (24%) occurred when vetch shoot N content was only 120 kg·ha-1 (107 lb/acre) (1996) and inorganic N was not supplied. In 1994, the vetch/rye biculture supplied sufficient N for maximum corn yields, but addition of inorganic N increased yields by more than 50% in 1995 and 1996. Under tilled conditions, the vetch N contribution to corn appeared to equal (1996) or exceed (1994 and 1995) 82 kg·ha-1 (73 lb/acre) of N supplied as ammonium nitrate, whereas a mean value of 30 kg·ha-1 (27 lb/acre) was obtained for the biculture cover crop (1995 and 1996). No significant effects of tillage on sweet corn population densities were detected following vetch, but no-tillage significantly reduced corn population densities following rye (17%) or biculture (35%) cover crops compared to tillage. No-tillage did not reduce yields from emerged seedlings (per plant basis) for any cover crops. Vetch appeared to be a satisfactory N source for sweet corn when vetch N content was ≥150 kg·ha-1, and it could be used with no-tillage without yield reductions.

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Anthony F. Silvernail and Gary R. Cline

Effects of tillage, winter cover crops, and inorganic N fertilization on watermelon production were examined in a split-plot factorial experiment. Main plots received tillage or no tillage, whereas cover crops consisted of hairy vetch, winter rye, or a mix. Nitrogen treatments consisted of plus or minus addition of ammonium nitrate. Following melons not receiving inorganic N, vetch produced cover crop total N yields of ≈130 kg·ha–1, which were four times greater than those obtained with rye. Melon yields and foliar N concentrations obtained without inorganic N fertilization following vetch were similar to those obtained with N fertilization following rye. Available soil N in vetch treatments remained significantly (P < 0.05) higher than in rye treatments for ≈70 days after melon planting and was greater in tilled treatments. Tillage significantly (P < 0.05) reduced melon yields by 20% and also reduced soil temperatures compared with no-till treatments. We conclude that N fixed by vetch could sustain watermelon production and no tillage may be useful when soil erosion is a problem.

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Gary R. Cline and Anthony F. Silvernail

A split-plot factorial experiment examined effects of tillage and winter cover crops on sweet corn. Main plots received tillage or no tillage. Cover crops consisted of hairy vetch, winter rye, or a mix, and N treatments consisted of plus or minus N fertilization. No significant effects of tillage on sweet corn yields were detected. Following corn not receiving inorganic N, vetch produced cover crop total N yields of 130 kg·ha–1 that were over three-times greater than those obtained with rye. Following rye winter covercrops, addition of ammonium nitrate to corn significantly (P < 0.05) increased corn yields and foliar N concentrations compared to treatments not receiving N. However, following vetch, corn yields and foliar N concentrations obtained without N fertilization equaled those obtained with N fertilization following rye or vetch. Available soil N was significantly (P < 0.05) greater following vetch compared to rye for ≈9 weeks after corn planting and peaked ≈4 weeks after planting. It was concluded that no-tillage sweet corn was successful and N fixed by vetch was able to sustain sweet corn production.

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Anthony F. Silvernail and Gary R. Cline

The effects of cover crop, tillage, and N fertilization on yields of `Paladin' watermelon (Citrullus lanatus) were analyzed by determining available soil N levels, foliar N content, and relative greenness with a SPAD-502 chlorophyll meter. Analyses from all three analytical procedures identified N deficiencies in watermelon with their respected measurements. Available soil N analyses indicated that soil N levels below 40 mg·kg–1 at vining caused dramatic decreases in yields, while the level needed to ensure maximal yields during the same period was 100 mg·kg–1. Results from foliar and SPAD tests indicated that plants with foliar N levels below 42 g·kg–1 and SPAD readings below 40 SPAD units at anthesis will have suppressed yields. Optimal foliar N levels and SPAD readings required for maximum yields were 50 g·kg –1 and 48 SPAD units, respectively. The main difference among all three N testing procedures was that available soil N analysis was able to detect possible deficiencies two to three weeks before either the foliar or SPAD analysis. Differences in yield between plants from conventionally tilled plots and no-till plots were not significant. However, inorganic N fertilization significantly increased yields in watermelon following both rye (Secale cereale) and mix cover crop treatments. Watermelon yields of plants following the hairy vetch (Vicia villosa) cover crop treatment showed no response to inorganic N fertilization. Of the three cover crop treatments, the addition of N fertilizer had the most effect in the rye treatment.

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Gary R. Cline and Anthony F. Silvernail

A split-plot factorial experiment examined effects of tillage and winter cover crops on `Merit' sweet corn in 1994, 1995, and 1996. Main plots received tillage or no-tillage. Cover crops consisted of hairy vetch, winter rye, or a mix, and N treatments consisted of plus or minus inorganic N fertilization. The shoot N contents of vetch and mix cover crops ranged from 100 to 150 kg/ha, whereas N contents of rye were usually <50 kg/ha. In 1994 and 1995, vetch shoot N contents were 150 kg/ha, and corn yields following vetch were not significantly affected by addition of inorganic N fertilizer. In 1996, vetch N contents only equaled 120 kg/ha, and corn yields were significantly increased by addition of inorganic N. Supplemental N was also required to obtain maximum yields following mix and rye cover crops in all years, even though the N contents of vetch and mix cover crops were normally similar. Measurements of corn foliar N and available soil N were in agreement with the yield results. No-tillage did not significantly affect corn yields following vetch. However, no-till corn yields were reduced with rye (1995) and the mix (1995 and 1996) as a result of reduced corn plant population densities. Reliable tillage results were not obtained for 1994. It was concluded that a vetch cover crop could adequately supply N to sweet corn if vetch N content was at least 150 kg/ha. Sweet corn following rye or vetch/rye mix cover crops required additional N for optimal yields. Significant N in the mix cover crop was probably immobilized as the rye component decomposed. No-till sweet corn was grown successfully following vetch, but yields were often reduced with the mix or rye cover crops.

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Gary R. Cline and Anthony F. Silvernail

A split-plot factorial experiment was conducted to examine effects of tillage and winter cover crops on sweet corn. Main plots received tillage or no tillage. Cover crops consisted of hairy vetch, winter rye, or a mix. Nitrogen treatments consisted of either adding or not adding NH4NO3 at recommended rates. No significant effects of tillage on sweet corn yields were detected, although yields with tillage were slightly greater. Following rye winter cover crops, adding NH4NO3 to corn significantly (P ≤ 0.05) increased yields by 56% compared to treatments not receiving N. However, following vetch, corn yields obtained without N fertilization equaled those obtained with N fertilization following rye or vetch. It was concluded that 1) nontilled sweet corn was successful and 2) N2 fixed by vetch was able to sustain sweet corn production completely and was equivalent to a minimum of 70 kg N/ha.

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Gary R. Cline, John D. Sedlacek, Steve L. Hillman, Sharon K. Parker, and Anthony F. Silvernail

Organic methods for managing striped cucumber beetles (Acalymma vittatum) and spotted (Diabrotica undecimpunctata) cucumber beetles were examined in the production of watermelon (Citrullus lanatus) and muskmelon (Cucumis melo) using sticky traps to monitor beetle populations. In 2002, the numbers of trapped striped and total (striped + spotted) cucumber beetles were significantly (P ≤ 0.05) reduced by the combined use of three companion plants thought to repel cucumber beetles [radish (Raphanus sativus), tansy (Tanacetum vulgare), and nasturtium (Tropaeolum spp.)] or by the combined use of three companion plants known to attract beneficial insects [buckwheat (Fagopyrum esculentum), cowpeas (Vigna unguiculata), and sweetclover (Melilotus officinalis)]. In 2003 and 2004, the single companion plant treatment consisted of the combined use of radish and buckwheat. In 2003, use of aluminum-coated plastic mulch (Al-plastic) or companion plants significantly increased muskmelon yields and vine cover, while significantly reducing numbers of trapped striped, spotted, and total cucumber beetles. The use of pyrethrin insecticide did not significantly affect muskmelon yields or vine cover. In 2004, the beneficial effects of companion plant and Al-plastic treatments on muskmelon yields and vine cover were also significant and similar to those in 2003; however, these treatments only affected early season numbers of trapped beetles. The use of rowcovers significantly increased muskmelon yields and vine cover in 2003 and 2004 and did not affect beetle populations after rowcover removal. It was concluded that use of companion plants and Al-plastic increased muskmelon yields and vine cover while reducing populations of cucumber beetles, particularly striped cucumber beetles. The use of rowcovers also increased muskmelon yields and vine cover.