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Peter L. Minotti, Donald E. Halseth, and Joseph B. Sieczka

Experiments were conducted at Freeville, NY and Riverhead, NY with 0-280 kg/ha of N banded. Tissue samples (both petioles and whole leaves) were taken 5 times starting 32 days from planting. There was a marked increase in yield and specific gravity from the first 112 kg/ha of N and in most cases from an additional 56 kg/ha of N. Both petiole and whole leaf nitrate were sensitive to changes in fertilizer rate that resulted in yield changes. We were encouraged by results obtained with “quick” tests on fresh sap since the pattern paralleled that obtained with traditional lab analysis of dried ground petioles. Although nitrate concentrations did not vary markedly across the varieties used there were substantial differences due to location even when the yield response curve was similar. Rate of N for rate of N, the Freeville samples were substantially higher in nitrate than those from Long Island, except at the 0 N rate, suggesting that the difference is not due to soil residual N.

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Timothy K. Hartz, P. R. Johnstone, E. Williams, and R.F. Smith

plant tissue testing in California Univ. Calif Bulletin 1879 Elwali, A.M.O. Gascho, G.L. Sumner, M.E. 1985 Sufficiency levels and DRIS norms for 11 nutrients in corn Agron. J. 77 506 508

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Timothy K. Hartz and Thomas G. Bottoms

520 524 Lorenz, O.A. Tyler, K.B. 1983 Plant tissue analysis of vegetable crops 24 29 Reisenaur H.M. Soil and plant tissue testing in California California Coop. Ext. Bul. 1879 Mitchell

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Aki Kubota, Thomas L. Thompson, Thomas A. Doerge, and Ronald E. Godin

This study was conducted to evaluate the accuracy of sap analysis using a portable nitrate ion meter for cauliflower (Brassica oleracea L. Botrytis Group, cv. Candid Charm) petiole nitrate determination. The relationship between NO3-N concentration in fresh petiole sap and in dried petiole tissue was studied for cauliflower grown in southern Arizona during the 1993–94 and 1994–95 growing seasons. Experiments were factorial combinations of three water rates and four N rates, both ranging from deficient to excessive. Petioles were collected throughout each season and were split for analysis of sap NO3-N and dried petiole NO3-N. Linear correlations between the two methods were similar in both seasons, with no consistent effect due to water application rate or crop maturity. Therefore, a single regression equation was derived: petiole sap NO3-N (mg·liter–1) = 0.047 × dry petiole NO3-N (mg·kg–1) + 218 (r2 = 0.772). This equation can be used to relate sap test measurements to existing guidelines for NO3-N concentrations in cauliflower petioles. These results suggest that the quick sap test, using the portable nitrate ion meter, is a valuable technique for monitoring N status of cauliflower.

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George Hochmuth, Osmar Carrijo, and Ken Shuler

Tomato (Lycopersicon esculentum Mill.) was grown in southeastern Florida on sandy soils that tested very high in Mehlich-1 P to evaluate the yield response to P fertilization. One location was used in 1995–96, another in 1996–97. Prefertilization soil samples contained 290 (location 1) and 63 (location 2) mg·kg–1 Mehlich-1 P. Both soil test results were interpreted as very high in P, and P fertilizer was not recommended for the crop. Fertilizer treatments at both sites were 0, 25, 50, 100, 150, and 200 kg·ha–1 P. Neither total marketable yield nor yield in any fruit size category was affected by P fertilization in either season. Amounts of cull (undersized or misshapened) fruits increased quadratically with P fertilization in the second season. Whole-leaf P concentrations increased linearly or quadratically with P application, depending on sample periods, and were always above sufficiency values. Although many tomato growers apply P fertilizer irrespective of soil test recommendations, our results showed that added P was not needed on soils testing very high in P. Furthermore, withholding P applications to soils with high P concentrations will minimize potential P pollution of surface water and groundwater.

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S.J. Breschini and T.K. Hartz

Trials were conducted in 15 commercial fields in the central coast region of California in 1999 and 2000 to evaluate the use of presidedress soil nitrate testing (PSNT) to determine sidedress N requirements for production of iceberg and romaine lettuce (Lactuca sativa L.). In each field a large plot (0.2-1.2 ha) was established in which sidedress N application was based on presidedress soil NO3-N concentration. Prior to each sidedress N application scheduled by the cooperating growers, a composite soil sample (top 30 cm) was collected and analyzed for NO3-N. No fertilizer was applied in the PSNT plot at that sidedressing if NO3-N was >20 mg·kg-1; if NO3-N was lower than that threshold, only enough N was applied to increase soil available N to ≈20 mg·kg-1. The productivity and N status of PSNT plots were compared to adjacent plots receiving the growers' standard N fertilization. Cooperating growers applied a seasonal average of 257 kg·ha-1 N, including one to three sidedressings containing 194 kg·ha-1 N. Sidedressing based on PSNT decreased total seasonal and sidedress N application by an average of 43% and 57%, respectively. The majority of the N savings achieved with PSNT occurred at the first sidedressing. There was no significant difference between PSNT and grower N management across fields in lettuce yield or postharvest quality, and only small differences in crop N uptake. At harvest, PSNT plots had on average 8 mg·kg-1 lower residual NO3-N in the top 90 cm of soil than the grower fertilization rate plots, indicating a substantial reduction in subsequent NO3-N leaching hazard. We conclude that PSNT is a reliable management tool that can substantially reduce unnecessary N fertilization in lettuce production.

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Erin E. Gamrod and Holly L. Scoggins

Grown as an annual in most of the United States, Strobilanthes dyerianus Mast. has become increasingly popular in summer landscapes partially due to its superior performance in hot and humid conditions. At present, there is no published research on the nutritional requirements of S. dyerianus. Our study examined growth and foliar elemental response to different levels of fertilizer. Rooted cuttings were transplanted and grown with 0, 100, 200, 300, and 400 mg·L–1 N from 5N–2.2 P–12.4 K fertilizer as constant liquid feed. Plants were irrigated whenever the volumetric water content of the substrate was <20% as determined with a Theta Probe moisture meter. Weekly pH and electrical conductivity (EC) were monitored using the pour through method. Eight weeks after initiation of treatment, dry weight and leaf area was measured. Recently mature leaf tissue was analyzed for total N, P, K, Ca, Mg, S, Fe, Mn, B, Cu, Zn, and Mo. There were no significant differences in plant quality under the 100, 200, 300, or 400 mg·L–1 N treatments. The largest plants, based on leaf area and shoot dry weight, were produced with 200 mg·L–1 N. Compared to recommended EC levels for bedding plants, the treatments receiving 300 and 400 mg·L–1 N had excessively high levels of substrate soluble salts though overall plant quality was not reduced. The increase in fertilizer concentration yielded a linear increase in tissue concentration of N, P, and K and a linear decrease in tissue concentration of Ca and Mg.

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T.K. Hartz, M. LeStrange, and D.M. May

The response of bell pepper (Capsicum annuum L.) to five rates of N fertigation between 0 and 336 kg N/ha was studied at two drip-irrigated sites [Univ. of California, Davis (UCD) and West Side Field Station, Five Points (WSFS)] in California in 1992. Nitrogen application, in the form of a urea: ammonium nitrate mixture (UN-32), was applied in eight (WSFS) or 10 (UCD) equal weekly increments, beginning after transplant establishment. At both sites, fruit yield and mean fruit size peaked at 252 kg N/ha, with additional N retarding crop productivity. Maximum fruit yield was obtained by fertility treatments that maintained petiole NO3-N concentration >5000 μg·g-1 through the early fruit bulking period. Two techniques for monitoring crop N status, designed for field use, were evaluated. There was a close relationship between the NO3-N concentration of fresh petiole extracts, as measured by a portable, battery-operated nitrate selective electrode, and dry tissue analyzed by conventional laboratory technique (r2 = 0.89). Relative chlorophyll concentration, measured nondestructively by a dual-wavelength leaf absorbance meter, was poorly correlated with whole-leaf N concentration (r2 = 0.55). However, the ratio of such chlorophyll readings for a treatment compared to an in-field reference of known N sufficiency (252 kg·ha-1 treatment) showed promise as a technique for identifying N deficiency.

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Xia Xu and Charles F. Mancino

Annual bluegrass (Poa annua L.) is becoming an important component of golf course putting greens. A greenhouse sand culture experiment was conducted to study the zinc (Zn) requirements of three genotypes of flowering annual bluegrass (FAB) and three genotypes of vegetative annual bluegrass (VAB), which were compared with the three parents of `Penncross' creeping bentgrass [Agrostis stolonifera L. (CB)]. Clonally propagated plants were grown in sand culture without Zn for 6 weeks prior to the initiation of the Zn treatments. The plants were then irrigated for 3 weeks with half-strength Hoagland's nutrient solution containing 0, 2.5, 5.0, or 40 mg·L-1 Zn from ZnSO4. Color was the only parameter affected by genotype; each genotype showed a significant quadratic response to increasing levels of Zn, with highest color ratings occurring at 2.5 mg·L-1. No genotypic differences were observed among CB, VAB, and FAB for shoot fresh and dry weight, root dry weight, or shoot tissue Zn concentrations. Shoot dry weight of all genotypes increased quadratically with Zn levels. Root dry weights of both VAB and FAB increased, while that of CB remained unchanged, as Zn level increased. Zinc concentrations in shoot tissue increased linearly as Zn level increased. Shoot Zn concentrations were higher in both VAB and FAB than in CB at each Zn level, but differences between VAB and FAB were insignificant. Maintaining shoot Zn concentrations below 109 mg·kg-1 in CB and 200 mg·kg-1 in VAB or FAB prevented Zn phytotoxicity from occurring.

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Xia Xu and Charles F. Mancino

Many biotypes of annual bluegrass (Poa annua L.) are found on golf course putting greens. Although normally considered an invasive weed, annual bluegrass can provide as good a putting surface as creeping bentgrass (Agrostis palustris Huds.). The most desirable biotypes of annual bluegrass are primarily vegetative and have a low flowering frequency. Whether the nutritional requirements of annual bluegrass biotypes differ from one another or from creeping bentgrass is unknown. The response of three flowering (FAB, high seedhead production) and three vegetative (VAB, low seedhead production) biotypes of annual bluegrass (AB), and the three parents of `Penncross' creeping bentgrass (CB) to varying levels of iron (Fe) in greenhouse sand culture was investigated. After establishment, clones were grown for 3 weeks and irrigated with a half-strength Hoagland's solution containing 0, 2, 4, 6, and 8 mg·L-1 Fe in citrate-Fe. Shoot and root responses to Fe were similar for the VAB and FAB biotypes. However, VAB had higher color ratings (darker green leaf color) with Fe treatment level at 4 mg·L-1 than did FAB or CB, which required 6 mg·L-1 Fe for acceptable color. Growth of creeping bentgrass was greater than that of annual bluegrass at every Fe level tested. Shoot dry weights of CB increased significantly with Fe treatment level up to 6 mg·L-1. Shoot dry weight of AB increased up to 4 mg·L-1 Fe and then declined at ≥6 mg·L-1. Root growth of CB increased up to 6 mg·L-1 Fe, but then decreased significantly at 8 mg·L-1 Fe. Root growth of AB increased slightly up to 4 mg·L-1 Fe and then declined at 6 and 8 mg·L-1. Shoot tissue concentrations of Fe were similar for AB and CB at each Fe rate tested except at 8 mg·L-1 Fe, where Fe levels in CB were significantly lower. Based on this work, creeping bentgrass and annual bluegrass respond differently to Fe nutrition, but different biotypes of annual bluegrass appear to respond similarly.