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Greg D. Hoyt

A no-till sweetcorn strip-till tomato rotation was established to determine whether a grass or legume winter cover crop would provide greater summer mulch and more soil inorganic nitrogen from residue decomposition. Sweetcorn yields improved as N rate increased in rye residue and bare soil, but only increased at the 50 kg N/ha rate in vetch residue. Strip-till tomato yields improved with all N rates for all covers. Total soil N and C were greater in both the vetch and rye residue treatments than the bare soil. Fertilizer N addition did not affect changes in total N or C percentages. Greater soil nitrate was measured beneath vetch residue at spring planting than in the rye residue or bare soil surface.

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Oswaldo A. Rubio, Patrick H. Brown and Steven A. Weinbaum

Leaf N concentrations (% dry wt) appear relatively insensitive to high levels of applied fertilizer N (Weinbaum et al, HortTechnology 1992). This insensitivity may be attributable to growth dilation, lack of additional tree N uptake, a finite capacity of leaves to accumulate additional N or our inhability to resolve a limited increment. Our objective was to asses the relative accumulation of mobile forms of N (NO3, NH4 and amino acids) relative to a total N over a range of fertilizer N application rates in 3 year old, field-grown “Fantasia” nectarine trees. Between 0 and 136 Kg N/Ha/Yr we observed a linear relationship between N supply and all N fractions. Above 136 Kg N/Ha/Yr leaf concentrations of amino acids and total N remined constant, but NO3 and NH4 accumulation continued. These results suggest that leaf concentration of NO3 and NH4 are more sensitive indicators of soil N availability and tree N uptake than was total leaf N concentration.

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Danielle D. Treadwell, Nancy G. Creamer, Greg D. Hoyt and Jonathan R. Schultheis

soil N, residue quality and quantity of component cover species, tillage, climate, and soil characteristics. For optimum N availability to the subsequent crop, a C:N ratio of 20:1 to 30:1 at the time of kill is desired ( Creamer et al., 1997 ; Ranells

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M. Pilar Bañados, Bernadine C. Strik, David R. Bryla and Timothy L. Righetti

soil N levels throughout the active growth period of blueberry. No work has been published to date on N fertilizer uptake and partitioning in young, field-grown blueberry plants. The objectives of our study were to determine the impact of N fertilizer

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Qingren Wang, Waldemar Klassen, Yuncong Li, Merlyn Codallo and Aref A. Abdul-Baki

Intensive rainfall during summer causes substantial nutrient leaching in a subtropical region, where most vegetable lands lay fallow during this period. Also, an excessive amount of irrigation water supplied during the winter vegetable growing season leads to soil nutrient loss, which greatly impacts vegetable yields, especially in soils that possess a low capacity to retain soil water and nutrients. A 2-year field experiment was carried out to evaluate the effects of various summer cover crops and irrigation rates on tomato yields and quality, and on soil fertility in a subtropical region of Florida. The cover crops were sunn hemp [Crotalaria juncea (L.) `Tropic Sun'], cowpea [Vigna unguiculata (L.) Walp, `Iron Clay'], velvetbean [Mucuna deeringiana (Bort.) Merr.], and sorghum sudangrass [Sorghum bicolor × S. bicolor var. sudanense (Piper) Stapf.], with a weed-free fallow as a control. The cover crops were planted during late Spring 2001 and 2002, incorporated into the soil in the fall, and tomatoes [Lycopersicon esculentum (Mill.) `Sanibel'] were grown on raised beds during Winter 2001–02 and 2002–03, respectively. Irrigation in various treatments was controlled when tensiometer readings reached –5, –10, –20, or –30 kPa. The cover crops produced from 5.2 to 12.5 Mg·ha–1 of above ground dry biomass and 48 to 356 Mg·ha–1 of N during 2001–02 and from 3.6 to 9.7 Mg·ha–1 of dry biomass and 35 to 277 kg·ha–1 of N during 2002–03. The highest N contribution was made by sunn hemp and the lowest by sorghum sudangrass. Based on 2-year data, tomato marketable yields were increased from 14% to 27% (p ≤ 0.05) by growing cover crops, and the greatest increase occurred in the sunn hemp treatment followed by the cowpea treatment. Irrigation at –10, –20, and –30 kPa significantly improved marketable yields by 14%, 12%, and 25% (p ≤ 0.05) for 2001–02, and 18%, 31%, and 34% (p ≤ 0.05) for 2002–03, respectively, compared to yields at the commonly applied rate, –5 kPa (control). Irrigation at –30 kPa used about 85% less water than at –5 kPa. Yields of extra-large fruit in the sunn hemp and cowpea treatments from the first harvest in both years averaged 12.6 to 15.2 Mg·ha–1, and they were significantly higher than yields in the fallow treatment (10.2 to 11.3 Mg·ha–1). Likewise at –30 kPa yields of extra-large fruit from the first harvest for both years were 13.0 to 15.3 Mg·ha–1 compared to 9.8 to 10.7 Mg·ha–1 at –5 kPa. Soil NO3-N and total N contents in sunn hemp and cowpea treatments were significantly higher than those in fallow. The results indicate that growing legume summer cover crops in a subtropical region, especially sunn hemp and cowpea, and reducing irrigation rates are valuable approaches to conserve soil nutrients and water, and to improve soil fertility and tomato yields and quality.

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Rafael A. Muchanga, Toshiyuki Hirata and Hajime Araki

and N as stocks is essential to understand changes in the whole soil C and N pools as affected by management practices such as cover cropping and compost application. The quality of organic residues applied to the soil (N content or C:N ratio) is a key

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M. Lenny Wells

may result in overapplication of fertilizer. In addition, proper timing of N applications based on soil N dynamics and plant demand can play a large role in the efficient use of fertilizer N. The in situ soil core technique can be helpful in evaluating

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David Sotomayor-Ramírez, Miguel Oliveras-Berrocales and Linda Wessel-Beaver

., 2002 ; Olson et al., 2011 ). In contrast, tropical pumpkin has a deeper root system that would be expected to take up residual soil N. Thus, fertilizer rates for tropical pumpkin are usually lower, in the range of 50 to 75 lb/acre of N in rotation

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S. Castro Bustamante and T.K. Hartz

any growth stage. Achieving synchrony between soil N availability and crop N demand has been recognized as a central challenge of organic N management ( Berry et al., 2002 ; Bhogal et al., 2001 ; Gaskell and Smith, 2007 ; Gill et al., 1995 ; Hatch

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Luther C. Carson, Monica Ozores-Hampton, Kelly T. Morgan and Steven A. Sargent

, source [mixed N (54% NH 4 + , 46% NO 3 – ) compared with urea-N], release duration, and bed placement on marketable tomato yield, LTN content, post-season soil N content, and post-harvest fruit firmness and color during the fall. Materials and Methods A