Four trees were identified for targeted 15 N enrichment during the summer 2010. Treatments of 15 NH 4 NO 3 and NH 4 15 NO 3 (10% 15 N a.e.) were pulse-injected from hour 0 to hour 6 through a static sprinkler system. Gas sampling was conducted at 18 and 42 hours. Soil sampling was conducted in duplicate to 0-10, 11-20, 21-30, 3140 and 41-50 cm at 6, 18 and 42 hours. Soil was oven-dried and roots were dry-sieved into fractions separated by diameter. Soil N was extracted in 2M KCl and diffused into 15 NH 4 + and 15 NO 3 fractions. Soil, roots and fruits were ground to pass through a 2mm sieve and packed into tin capsules. Samples for isotopic analysis were sent to the UC Davis Stable Isotope Facility. Crop Export The isotope application injected through three fanjets and two treatments allowed for the enrichment of four almond trees in total. One tree in each treatment received a full rate and one tree in each treatment received a half rate. Despite the inability for replication distinct differences were observed.

The optimum yield-scaled global warming potential (GWP) of perennial crops on arid land requires effective strategies for irrigation and fertilization. In 2009-2010, N2O emissions and CH4 oxidation were measured from an almond [Prunus dulcis (Mill.) D.A. Webb] production system irrigated with nitrogen (N) fertilizers. Individual plots were selected within a randomized complete block design with fertilizer treatments of urea ammonium nitrate (UAN) and calcium ammonium nitrate (CAN). Event-related N2O emissions from irrigation and fertilization were determined for seasonal periods of post-harvest, winter, spring and summer. Peak N2O emissions in summer occurred within 24h after fertilization, and were significantly greater from UAN compared to CAN (p<0.001). Cumulative N2O emissions from UAN were on average higher than CAN though not significantly different. Air temperature, water-filled pore space (WFPS), soil ammonium (NH4+) and soil nitrate (NO3-) showed significant positive correlation with N2O emissions and significant negative correlation was found for the number of days after fertilization (DAF). The percentage of N2O loss from N fertilizer inputs was 0.23% for CAN and 0.35% for UAN while CH4 oxidation offset 6.0-9.3% of N2O emissions. Total kernel yield was not significantly different between fertilizer treatments. Yield-scaled GWP for almond from CAN (60.9 kg CO(2)eq Mg-1) and UAN (91.9 kg CO(2)eq Mg-1) represent the first report of this metric for a perennial crop. These results outline effective irrigation and fertilization strategies to optimize yield-scaled GWP for almond on arid land. (C) 2012 Elsevier B.V. All rights reserved.

Greenhouse gas emissions from agriculture and forestry in California are estimated at approximately 8.3% of the total production of 493 million metric CO2-equivalent tons (California Energy Comission (CEC); Research Roadmaps for Greenhouse Gas Inventory Methods; Sacramento, CA, 2005), of which nitrogen (N) fertilizers applied to soils and soil management are estimated to be the major sources of N2O production. Of the approximate 3.89 million hectares (ha) of intensively irrigated cropland in California (California Department of Water Resources (DWR); Agricultural Water Use; Sacramento, CA, URL http://www.water.ca.gov/wateruseefficiency/agricultural/), approximately 1.17 million ha are planted to orchards and vineyards. This acreage is irrigated and fertilized with N using microirrigation systems and liquid N fertilizers (fertigation). Understanding biophysical factors that regulate N2O emissions during fertigation will be necessary for scaling exercises, and for developing sustainable management practices. We present ongoing work showing spatial variation in microbial enzyme activity in the microirrigation wet-up zone related to N2O emissions and indicating that denitrifying microorganisms may be more abundant in the drip zone. Spatiotemporal variation in N2O emissions around conventional aboveground drip and stationary fanjet micro-sprinkler systems in grape, a non-N-intensive perennial crop, and almond, a N-intensive perennial crop were well characterized using 3-dimensional modeling exercises. The quantity of N2O emitted was lower when N was applied through stationary fanjet sprinklers than it was for conventional drip application in an almond orchard on a sandy loam soil.

Abstract Little information is available about how farmers in transition to organic practices should manage short- and long-term N fertility. The objectives of this research were (1) to evaluate the leguminous cover crops lablab (Dolichos lablab L.), soybean (Glycine max L.), sunn hemp (Crotalaria juncea L.) and a mixture of sunn hemp and cowpea (Vigna sinensis Endl.) as N sources; (2) to compare N availability and broccoli yield when cover crops were incorporated with conventional tillage (CT) or retained as a surface mulch using no-tillage (NT) practices; and (3) to quantify the amount of supplemental sidedress nitrogen required to maximize the yield of organic broccoli (Brassica oleracea Group Italica) on transition soils. Broccoli was grown during the first year after organic transition in the spring and fall of 2006 at the Kentland Agricultural Research Farm near Blacksburg, VA. Spring (P<0.001) and fall (P<0.001) broccoli yield increased as the rate of sidedress N was increased up to 112 kg N ha−1, and showed a quadratic correlation with leaf N (P=<0.001, R2=0.80 and P=<0.001, R2=0.38, respectively). There was no difference in spring broccoli yield between CT and NT; however, CT produced the highest yield in the fall crop. At low sidedress N rates, leaf N was highest in CT plots, but tillage had no effect on N uptake at high N rates. This indicates that early season and perhaps total plant-available mineralized N was greater in CT than NT; however, potential N deficiency in NT soil may be compensated by sidedress N. Broccoli yield was not affected by leguminous cover crop, even though the quantity of cover crop biomass and N contribution was different among species. This suggests that N availability from leguminous cover crops may be impacted by other ecological processes such as soil microbial activity. This study shows that organic CT and NT growers can maximize broccoli yield in transition soils low in N availability, by using leguminous cover crops in combination with moderate amounts of sidedress N.

An open-market window has been identified in Virginia for fall broccoli (Brassica oleracea var. italica). Vegetable producers using plasticulture systems can capitalize on this opportunity by growing broccoli as a second crop after summer vegetables. The objective of this project was to evaluate suitability of two broccoli cultivars, Everest and Gypsy, for the fall production of large single-heads (>6 inches in diameter) for the fresh market. Planting density and rate of nitrogen (N) fertilizer (25, 60, and 100 lb/acre N) effects on yield characteristics were evaluated in a plasticulture system during a 3-year study (2003–05) conducted with broccoli transplants at the Virginia Polytechnic Institute and State University Kentland Agricultural Research Farm near Blacksburg, VA. The percentage of large heads was cultivar, plant density, and N rate dependent. The midseason ‘Gypsy’ produced significantly higher total yield and head weight compared with the early-season ‘Everest’. The optimum density to maximize floret production per area was 12,500 plants/acre and a supplemental N rate of 100 lb/acre. This N rate significantly (P < 0.002) improved marketable yield, large head yield, and leaf N accumulation compared with the lower rates. The data indicate that the feasibility of growing fall broccoli using a plasticulture system depends on the number of large heads produced for the fresh market. This in turn will depend on the choice of cultivar, stand establishment, and the requirement for supplemental N fertilizer over the residual level available in the soil after the first crop.