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R.F. Korcak

The beneficial influences of gypsum on soil improvement and plant growth have been well-documented, Among these benefits are reclamation of sodic soils, alleviation of subsoil acidity problems, and contribution of Ca and S as nutrients. There are three industrial byproducts that contain significant amounts of gypsum. Phosphogypsum is probably the best-known byproduct gypsum source; the others are clean-air technology coal combustion byproducts, namely fluidized bed combustion and flue gas desulfurization residues. This review summarizes the beneficial chemical and physical effects of gypsum on soil properties and the resultant benefits on plant growth. Where applicable, emphasis is placed on potential uses and limitations of byproduct gypsum sources on horticultural crops. The potential for incorporating these materials in artificial mixtures with organic materials is discussed.

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Aref A. Abdul-Baki, John R. Teasdale, and Ronald F. Korcak

A 3-year experiment was conducted to determine the optimum fertilizer N requirements of fresh-market tomato (Lycopersicon esculentum Mill.) `Sunbeam' grown on a hairy vetch (Vicia villosa Roth.) or black polyethylene mulch. In 1993 and 1994, four rates of fertilizer N (0, 56, 112, and 168 kg·ha-1) as water-soluble NH4NO3 were applied in 14 equal applications through the trickle irrigation system starting 1 week after planting. Four additional rates (224, 280, 336, and 392 kg·ha-1) were applied in 1995 to assess the plant response to supra-optimal levels of N. Hairy vetch produced 3.3–4.5 t·ha-1 of above-ground biomass and a total N content of 126–169 kg·ha-1 in the above-ground biomass. Leaf N content at 7 weeks after transplanting of tomatoes correlated positively with yield from black polyethylene but did not correlate with yield from the hairy vetch plots where leaf N content was optimal at all N rates. Predicted tomato yields were higher for the hairy vetch than for the black polyethylene treatment at all applied N rates in all years. Tomatoes grown in black polyethylene required N at 130 to 144 kg·ha-1 to achieve yields equivalent to those grown following unfertilized hairy vetch. Tomato yield increased in response to applied N in both mulches in all 3 years; optimum N rates of 89 and 190 kg·ha-1 in hairy vetch and black polyethylene, respectively, were predicted by a linear plateau model, and 124 and 295 kg·ha-1 by a quadratic plateau model. The linear plateau model is recommended because it would allow less N to become available for runoff and leaching.

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Aref A. Abdul-Baki, J.R. Teasdale, R. Korcak, D. Chitwood, and R Huettle

Fresh-market tomatoes (Lycopersicon esculentum Mill) cvs. Sunny and Sunbeam were grown in bare soil (BS), Horto paper (HP), black polyethylene (BP), hairy vetch (HV), crimson clover (CC), and hairy vetch plus rye (HVR) mulches. Yields were highest in HV (85.8 t·ha–1), followed by HVR 69.3 t·ha–1) and CC (65.7 t·ha–1), and averaged 47% above BP for the 3-year period. A 5- to 9-day earliness was exhibited by BP over other treatments. Fruit weight was significantly higher in all three organic mulch treatments than in the other three treatments. Mulch biomass was highest in HVR (5.91 t·ha–1), whereas N fixation was highest in HV (188 kg·ha–1). Tomato harvest was extended by the HV treatment over the BP treatment by 3 to 4 weeks, during which tomato prices were higher than those in early or mid-season.

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Aref A. Abdul-Baki, J.R. Teasdale, R. Korcak, D.J. Chitwood, and R.N. Huettel

A low-input sustainable agricultural system for the production of staked, fresh-market field tomatoes (Lycopersicon esculentum Mill.) is described. The system uses winter annual cover crops to fix N, recycle leftover nutrients, produce biomass, and prevent soil erosion throughout the winter and spring. Yields of tomato plants grown in hairy vetch (Vicia villosa Roth), crimson clover (Trifolium incarnatum L.), and rye (Secale cereale L.) plus hairy vetch mulches were higher than those grown in the conventional black polyethylene (BP) mulch system in 2 of 3 years. Fruit were heavier with the plant mulches than with BP mulch. Eight weeks after transplanting, N levels in tomato leaves were higher with plant than with BP mulch, although the plant mulch plots received only 50% of the N applied to the BP plots. The cover crops had no effect on populations of five phytoparasitic nematode species.