Seeming conflict between the need to use N fertilizers and the need to protect groundwater quality requires better tools for distinguishing between fertilizer applications that are essential and those that are excessive. Studies were conducted to evaluate NO‐3 concentration in corn (Zea mays L.) stalks at physiological maturity as the basis for a tissue test to characterize degree of N excess during corn production. Samples of the lower portion of corn stalks were collected from plots in N‐rate experiments at 18 site‐years in Iowa. Observed relationships between grain yields and stalk NO‐3 concentrations indicated sharp breaks between NO‐3 concentrations that were not adequate and those that were adequate for obtaining maximum or near‐maximum yields. When yields were near maximum, stalk NO‐3 concentrations increased linearly with amounts of N fertilizer applied. Stalk samples collected at various times after black layering showed that NO‐3 concentrations remained constant for at least 2 wk. These observations suggest that stalk NO‐3 concentration offers great potential as the basis for a tissue test to characterize degree of N excess during corn production.

Alfalfa (Medicago sativa L.) contributes substantial N to grain crops that follow, but there is uncertainty concerning the amounts. The objective of this study was to determine optimal rates of N fertilization for first‐year corn (Zea mays L.) grown after alfalfa. Fertilizer N was applied at seven rates, ranging from 0 to 200 lb/acre, at 29 trials conducted over 4 yr in northeast Iowa. Concentrations of soil nitrate in late spring and concentration of nitrate in cornstalks at the end of the season were used to help determine optimal N rates. Fertilizer significantly increased yields at six of the 29 trials. The rate of N fertilization most profitable when applied across the 29 fields was mainly determined by cost of fertilization and value of grain. At prices prevailing in the Corn Belt, applications of 0 and 25 lb N/acre were the most profitable. The soil test was most effective when used with a critical concentration of 14 ppm nitrate‐N to distinguish between soils that should and should not be fertilized. Nitrogen fertilization was most profitable when 50 lb/acre was applied to the three low‐testing soils, which gives a mean rate across all 29 trials of 5 lb N/acre. Both the soil test and the end‐of‐season cornstalk test should help producers recognize that little or no N is needed for first‐year corn after alfalfa. Research Question Alfalfa contributes substantial N to grain crops that follow, but there is uncertainty concerning the amounts. The objective of this study was to determine optimal rates of N fertilization for corn after alfalfa in northeast Iowa. Concentrations of soil nitrate in late spring and concentrations of nitrate in cornstalks at the end of the season were used to help identify optimal N rates. Literature Summary Numerous studies have shown that little yield response to applied N should be expected on first‐year corn after alfalfa. Other studies indicate that farmers frequently apply substantially more fertilizer N to corn after alfalfa than is required to attain maximum yields. Overapplication of fertilizer N reduces profitability of corn production and can cause nitrate contamination of water supplies. Study Description Nitrogen response trials were established on 29 fields from 1987 through 1990. Fertilizer N was applied at seven rates, ranging from 0 to 200 lb/acre. Except for fertilizer application and harvest, each trial was managed by the farmers. Alfalfa management usually consisted of three cuttings per year in all but the establishment year, and no field received a manure application for at least 3 yr before corn planting. Soil samples were collected when corn was 6 to 12 in. tall from the surface 1 ft layer of soil. Cornstalk samples were collected 1 to 3 wk after physiological maturity (black layer formation) by removing 8‐in. segments of stalk starting 6 in. above the ground. Applied Questions What was the corn grain yield response to N fertilization? Applications of fertilizer N significantly increased yields at six of the 29 trials. At each of these responsive trials there ...

In Florida, long-term results for identifying high yielding sugarcane (Saccharum spp.) cultivars have been better for Histosols (muck soils) than sand soils. We examined whether selection could be improved by comparing genotypes on a sand soil with and without added mill mud (MM) (in Florida, MM is primarily muck soil). One Erianthus and 31 sugarcane genotypes were planted in 2007 with MM at 0 or 1510 m 3 ha -1 in main plots and genotypes as subplots in a 3-yr eld experiment on a Margate sand soil (siliceous, hyperthermic Mollic Psammaquent). Commercial recoverable sucrose (CRS) (g kg -1 ), and cane (CY) and sucrose (SY) yields (Mg ha -1 ) were determined during the next 3 yr. Mill mud reduced CRS from 127 to 111 g kg -1 but increased cane and sucrose yields from 80 to 150 and 10 to 17 Mg ha -1 , respectively. Compared with the check of CP 89-2143, 2, 10, and 8 genotypes were di erentially a ected by soil treatment (P = 0.10) for CRS, CY, and SY, respectively. CP 01-2390 was the most adapted sand genotype; its CYs on sand with and without MM were 147 and 143 Mg ha -1 , respectively. Compared with previous research, CY responses were well predicted for ve genotypes, but poorly predicted for four genotypes in this study. Multiple locations are needed for sugarcane genotype selection on sand soils. Using a sand soil with and without added MM can be a useful supplemental, rather than singular approach for improving sugarcane genotype selection in Florida.

Four field experiments were conducted from 1990 to 1992 on Histosols in southern Florida to compare the relative response of various types of lettuce (Lactuca sativa L.) (i.e., leaf, Boston, Bibb, romaine, and crisphead lettuce) to P fertilization. All lettuce types showed large yield and quality responses to P fertilization. Because environmental conditions affected yield potential, P rates required for optimal yield varied for lettuce types across experiments. However, with the exception of Boston, the P rates required for optimal yield were similar when averaged over all experiments. Furthermore, the relationship between relative yield and soil-test P across all seasons showed that a similar soil-test P index level was required for maximum yield of all lettuce types. Overall, the results of this study suggest that existing soil-test-based fertilizer recommendations for crisphead lettuce are adequate for other lettuce types currently grown.

Sugarcane 'UFCP 74-1010' (Reg. No. CV-160, PI 673048) was released by the University of Florida and the USDA-ARS, Canal Point, for its potential use in cellulosic ethanol production. UFCP 74-1010, a cross between sugarcane (a complex hybrid of Saccharum spp.) cultivars CP 66-56-4 and CL 47-83. UFCP 74-1010 is a high iber sugarcane that has been released to improve biomass production for cellulosic ethanol production in Florida. UFCP 74-1010 is moderately resistant to smut (caused by Sporisorium scitamineum) with signiicantly lower infestation compared with a reference check, 'L 79-1002', under both natural environmental conditions and artiicial inoculations. UFCP 74-1010 is also resistant to brown rust (caused by Puccinia melanocephala H. and P. Sydow), orange rust (caused by P. kuehnii), and mosaic (caused by Sugarcane mosaic virus) and is moderately resistant to leaf scald [Xanthomonas albilineans (Ashby) Dawson]. Mean dry biomass yield of UFCP 74-1010 (29.2 Mg ha −1 ) was approximately 5% higher than L 79-1002 (27.9 Mg ha −1 ), averaged across eight location-years of ield trials. Plant composition of UFCP 74-1010 is similar to L 79-1002 with 41.9% cellulose, 27.8% hemicellulose, 22.4% lignin, 5.0% ash, and 1.6% structural protein. UFCP 74-1010 is released to be cultivated