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  • Author or Editor: Warren Roberts x
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Corn planted to originally acidic grassland soils with a low phosphorus (P) content and fertilized at normal rates produced low yields. A factorial study was designed with three application methods (banded, broadcast, tilled) at four rates (34, 67, 101, 134 kg/ha) P2O5. Sweet corn (Zea mays (L.) was planted in double rows on raised beds (0.9 m wide, 1.8 m centers) with 30 cm spacing in and between rows. Most yield parameters increased linearly with increasing rates of P. Banded P produced best yields, but growth was variable between the two double rows per bed. In a second study, P2O5 ranging from 0 to 403 kg/ha was applied by conventional methods. There was a positive response of most yield parameters to increasing rates of P. In a third study, soil plugs (2 cm diam., 10 cm depth) were removed 5 cm to the side of each plant. Rates of P2O5 ranging from 0 to 202 kg/ha were placed in the plugs. Yield responded positively to increasing rates of P. P applied in the plugs produced yield responses similar to P applied conventionally.

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The sweetpotato [Ipomoea batatas (L.) Lam] cultivars Jewel, Shore Gold, and Cordner, and the breeding line W241 were either 1) not flooded, 2) flooded for 5 days during midseason, or 3) flooded for 5 days just before harvest. Flooding just before harvest did not affect marketable yield, but flooding at midseason reduced marketable yield by 36% in 1989 and by 53% in 1990 and reduced the No. 1 grade yield by 46% in 1989 and by 57% in 1990. Marketable yield of `Jewel' was higher than that of `Cordner' in 1989, and that of `Shore Gold' exceeded that of `Jewel' in 1990. There were no interactions between flooding treatments and cultivars.

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The effects of cover crops and nitrogen on yield and insect damage of sweet corn were examined. In 1989, sweet corn was grown in bare soil plots, plots covered with rye (Secale cereale), and plots covered with hairy vetch (Vicia villosa). In 1990 a black plastic mulch treatment was substituted for the hairy vetch treatment. Each soil cover was fertilized with 45, 90, 134, or 179 kg/ha nitrogen (N) in 1989, and 34, 101, 168, 235, or 302 kg/ha N in 1990. Covers were planted in the fall, followed by sweet corn the following spring. There was no mowing or tilling of the cover crops.

Corn yields were lower each year in the rye covered plots. There were more corn earworms on the rye covered plots. Corn pollination was poorer on the rye covered plots, but responded positively to increasing rates of N.

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Sweet potatoes are an important crop in the southern U.S. The southern U.S. is subject to heavy rainfall at any time during the production season, and soils could be flooded for days. Previous work has shown that sweet potatoes flooded just prior to harvest exhibited increased decay during curing and storage. This study was designed to determine the effects of flooding at both mid-season and late-season on sweet potato yield. Four cultivars were grown in both 1989 and 1990. Each cultivar received a control treatment (no flooding), flooding halfway through the production season, and flooding just prior to harvest. Flooding was continuous for approximately 6 days. Yield was not significantly affected by late season flooding, but mid-season flooding reduced yields of all varieties. Yield reduction due to flooding at mid-season was in excess of 35% in 1989 and in excess of 50% in 1990.

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In fall of 1992, `Allstar' strawberries were planted in a greenhouse in round pots 25 cm wide and 22 cm tall Plants were grown in Peter's Professional Potting Soil that was amended to contain 0. 34, 67, or 135 kg nitrogen/ha, and 0 or 1.7 kg boron/ha. based on the surface area of the pots at media level The strawberries remained in the greenhouse throughout the fall, and were transferred outside for overwintering under row cover. In the spring of 1993, the plants were moved to a sheltered growing area. and the row cover was removed to allow for pollination Fruit were harvested 3 times per week and weight and number of fruit were recorded After harvest was complete. the plants were removed from the media. weighed, and analyzed for nutrient content Plants receiving boron but no nitrogen fertilizer had significantly higher boron concentration than plants receiving other combinations. Magnesium concentrations were significantly less in plants receiving the highest rates of nitrogen as compared to the other nitrogen rates Plant weight was not affected by the fertilization treatments. but fruit yield was significantly increased if N was added.

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Abstract

The University Arboretum is located on the Davis campus of the Univ. of California. It occupies about 100 acres along the banks of ancient Putah Creek and is close to the middle of the Great Central Valley of California. The prevailing climate closely resembles that of the Mediterranean region, with cool, wet winters and hot, dry summers in which a range of adapted plants will flourish. The extensive collections well illustrate the variety and brilliance of trees, shrubs, and perennials adapted to grow in such conditions.

Open Access

A factorial experiment with four mulch treatments (clear, black, or IRT plastic, and a non-mulched control), two planting types (seed vs. transplants), and two row cover treatments (with and without) was initiated to determine the harvest date of watermelon with these treatments. Experiments were planted in the field April 7. Row covers (Kimberly Farms, spunbonded polypropylene, 20 g·m-2) were suspended on wire hoops above selected plots. Soil temperatures at 5 cm, measured at noon, were lower in plots with row covers. On May 13, the row covers were in the process of being removed when a thunderstorm developed. One guard row remained covered during the storm. Hail ranging from 1.3 to 2.5 cm in diameter fell for 30 minutes, with a final accumulation of 5 cm of hail and 10 cm of rain. There was no noticeable difference between transplants and direct seeded plants, or among the different types of mulch, on resistance to hail damage. All plots that were not covered with row covers were totally destroyed. However, the area on which row covers had not been removed received only minor damage.

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Cabbage (Brassica oleracea L. Capitata) was grown for five years with treatments comparing no till and conventional production systems. Each year, raised beds were formed in the fall and selected plots were seeded with rye (Secale cereale). The rye was allowed to grow during the winter, and the following spring it was either mowed, killed with herbicide, or allowed to grow indefinitely. Different seeding rates of rye and different fertilizer rates were used. Some plots were mowed and the residue removed from the plots, while certain plots had no rye planted but received the rye residue that was removed from other plots. Rye was also gathered and pulverized, and the liquid extract removed from this suspension was sprayed onto plots. Cabbage was planted into each plot in the spring. The yield of cabbage grown in various rye-covered plots was compared to the yield from bare soil plots and from plots covered with black plastic mulch. In general, the plots covered with the various rye treatments had less yield than did the bare soil plots. Plots covered with black plastic mulch often had a greater yield than did the other plots.

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Raised beds (0.9 m wide, 1.8 m centers, 6.1 m long) were formed in Oct. 1988. Beds were either left bare or seeded with rye (Secale cereale) or hairy vetch (Vicia villosa). Plots were sprayed with glyphosate in April, 1989. Rye was completely killed, but hairy vetch was not. Bed height was maintained best with beds covered with rye. In a 3 by 4 factorial, four rates of nitrogen (45, 90, 134, and 179 kg/ha) were applied to each soil cover treatment. On April 17, cabbage (Brassica oleracea cv. Solid Blue 760) was transplanted two rows per bed, with 30 cm spacing in rows and between rows. There was no mowing or cultivating prior to transplanting. A linear increase in yield was observed with increasing applications of nitrogen. The cabbage yield was less in rye than in vetch orbare soil. The yield difference between rye and bare soil was more pronounced at the low rates of nitrogen than at the high rates of nitrogen. Cabbage grown in rye had significantly fewer aphids, thrips, and cabbage loopers than did cabbage grown in bare soil.

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Electrolyte leakage was used to quantify heat stress injury in `Early Calwonder' pepper (Capsicum annuum L.) leaf disks. Lethal temperatures were estimated from the midpoint of the sigmoidal response curve. An interaction between exposure temperature and duration was observed, with lethal temperatures decreasing linearly from 53 to 46C as exposure duration increased exponentially from 5 to 240 min. Exposure to two 7.5-min periods at 51.5C, interrupted by 4 hours at 21C, resulted in the same injury as a continuous 15-min exposure to 51.5C. Plants grown at 22/20C day/night cycles and held 24 hours at 38/30C had increased their heat tolerance by 3C, 51 to 54C; these plants reacclimated to 52C 48 hours after having been transferred back to 22/20C. Leaf disks acclimated significantly in vitro in 1 hour and were fully acclimated by 4 hours at 38C.

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