Robert W. Mullen

Root-zone temperature and nitrogen affect the yield and secondary metabolite concentration of fall- and spring-grown, high-density leaf lettuce.

BACKGROUND Understanding the effects of temperature and nitrogen levels on key variables, particularly under field conditions during cool seasons of temperate climates, is important. Here, we document the impact of root-zone heating and nitrogen (N) fertility on the accumulation and composition of fall- and spring-grown lettuce biomass. A novel, scalable field system was employed. RESULTS Direct-seeded plots containing a uniform, semi-solid, and nearly stable rooting medium were established outdoors in 2009 and 2010; each contained one of eight combinations of root-zone heating (-/+) and N fertility (0, 72, 144, and 576 mg day(-1)). Root-zone heating increased but withholding N decreased biomass accumulation in both years. Low N supplies were also associated with greater anthocyanin and total antioxidant power but lower N and phosphorus levels. Tissue chlorophyll a and vitamin C levels tracked root-zone temperature and N fertility more closely in 2009 and 2010, respectively. CONCLUSIONS Experimentally imposed root-zone temperature and N levels influenced the amount and properties of fall- and spring-grown lettuce tissue. Ambient conditions, however, dictated which of these factors exerted the greatest effect on the variables measured. Collectively, the results point to the potential for gains in system sustainability and productivity, including with respect to supplying human nutritional units.

Effect of Tillage and Anhydrous Ammonia Application on Nitrogen Use Efficiency of Hard Red Winter Wheat

ABSTRACT Nitrogen use efficiency (NUE) in cereal grain production is estimated to be 33% throughout the world, and can be lower when N is applied in single, pre-plant applications compared with split N applications. This study was conducted to evaluate tillage system and anhydrous ammonia (AA) application methods on yield, N uptake, and NUE in hard red winter wheat (Triticum aestivum L.), using a narrow (10 cm) nozzle spacing on a V-blade (Noble or sweep blade) applicator and wide (46 cm) nozzle spacing on a knife applicator. Over the four-year period evaluated, conventional tillage was significantly higher in grain yield in five of eight site years over no-till. However, no-till was significantly higher in grain yield at Lahoma in 2003 where the highest overall grain yield was observed. Mixed results were evaluated in NUE for tillage; four site years of no significant differences between tillage systems and the other four site years split evenly between conventional-till and no-till. The V-blade improved NUE in no-till for three site years at Lahoma, while the knife applicator increased NUE the initial year at Efaw in no-till. Previous crop residue disturbance averaged less than 15% for both AA applicators all four, site years. Mid-season plant populations taken during the 2003 and 2004 crop years were insignificant three of the four site years and plant population did not influence grain yield and NUE. No-till crop production reduced soil compaction at Efaw and the V-blade applicator reduced soil compaction within no-till at both locations. Although the no-till system showed the potential to produce grain yield and grain N levels comparable to conventional tillage, conventional tillage had a distinct advantage in grain yield and grain N uptake over the four-year duration of this study. The V-blade application method improved NUE in no-till at one site, potentially due to reduced soil compaction, but neither AA applicator showed an advantage in conventional tillage. Over the four years of this study no-till reduced soil compaction and conventional tillage produced higher grain yields, but no conclusive advantages were found in NUE for either tillage practice or AA application method.