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  • Author or Editor: J.C. Gilsanz x
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The objective of this work was to establish the dry-matter production and yield at different irrigation levels and moments of water application. An early cultivar, INIA-Sandu, was transplanted in Nov. 1996. Treatments were a combination of: no irrigation, irrigation at 25 kPa and 75 kPa of soil moisture tension during the first 60, 30 to 90, 60 to 120 days, and during all the cycle after crop establishment. Sequential samples were done throughout the growth cycle. The parameters evaluated were fresh and dry weight of leaves, stems, and roots. At the end of the crop cycle, yield was determined. Irrigation levels and early applications affected weight of leaves, stems, and roots. Yield was greater at early water applications during the growth cycle. Lower soil moisture tensions tend to have greater yields.

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A 3-year study of cover crops (rye + crimson clover or sudex) and vegetable rotation systems was conducted using a Norfolk sandy loam soil. Cash crops were planted on all plots each spring, and in the fall, crops were snap beans/squash, sudex, or fallow. Late incorporation of cover crops depleted soil water content, resulting in a need for irrigation before spring plantings. Sudex residue had a high C: N ratio, delaying the total mineralization of N. Potato yields were not affected by rotation treatments. Cover crops improved snap bean emergence and yield. Snap beans had a differential uptake of Fe, Al, and B with cover crops. Tomato growth and yield were reduced with winter cover crops. Fall squash yield was not influenced by rotations.

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Three studies were conducted at Clinton, N.C., to investigate the relationship between number of rows per bed, in-row spacing, and spear yield of asparagus (Asparagus officinalis L.) over 11 to 13 years. In the first study, increasing plant densities from 21,550 to 43,100 plants/ha by doubling the number of rows/bed increased the cumulative yield from 64% to 80% for three hybrid lines (`UC 157', `WSU 1', and `WSU 2') but only 6% for `Rutgers Beacon'. The effects of doubling the plant density were still apparent 13 years later. In the second study, yields of `Princeville' (`Mary Washington' selection) crowns, grown at densities from 14,000 to 86,000 plants/ha, were also increased for 8 years by doubling rows at various in-row spacings. In a third study, in which densities ranged from 21,000 to 387,900 plants/ha, the magnitude of the response to rows/bed was dependent on in-row spacing. Efficient use of bed space and the avoidance of crowding exerted a larger influence on productivity than did average planting density. The yield response to rows/bed was greater and more persistent through the years for wider in-row spacings. Spear size was only marginally responsive to rows per bed and in-row spacing.

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`Jewel' sweetpotato was no-till planted into crimson clover, wheat, or winter fallow. Then N was applied at 0, 60, or 120 kg·ha–1 in three equal applications to a sandy loam soil. Each fall the cover crop and production crop residue were plowed into the soil, beds were formed, and cover crops were planted. Plant growth of sweetpotato and cover crops increased with N rate. For the first 2 years crimson clover did not provide enough N (90 kg·ha–1) to compensate for the need for inorganic N. By year 3, crimson clover did provide sufficient N to produce yields sufficient to compensate for crop production and organic matter decomposition. Soil samples were taken to a depth of 1 m at the time of planting of the cover crop and production crop. Cover crops retained the N and reduced N movement into the subsoil.

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A vegetable production system using winter cover crops and N rates was evaluated for several years in Georgia, South Carolina, and North Carolina. Snap bean, cucumber, tomato, potato, and sweetpotato crops were tested at different locations. Cover crop plots produced higher yields and better quality in all locations as seasons progressed over 4 years. Soil N levels in fallow, wheat, and clover plots were similar at initiation, but N gradually increased in clover plots in successive years. Yield and quality of root crops improved with Crimson clover without N applications compared to fallow plots with 60 kg N/ha. Effects on yield and tuber size are discussed. Nitrate and NH4-N in the soil profile from 15- to 150-cm depth were monitored at all locations. Nitrogen availability, depletion, and leaching below the root zone were determined. At low N rate, clover plots had slightly higher NO3 in the soil profile; however, at high N rate, N supply by clover was not as critical, and N leaching was detected at much lower depths than at low N rates.

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