Long-term N fertilization and conservation tillage practices conserve surface but not profile SOC stocks under semi-arid irrigated corn

No tillage (NT) and N fertilization can increase surface soil organic C (SOC) stocks, but these gains are frequently not observed through the soil profile and could be subject to loss through subsequent tillage events. We evaluated a long-term irrigated continuous corn no-tillage (NT) and N rate study near Fort Collins, CO that was split into continuous NT or strip till (ST) treatments after five years. We measured grain and residue yields yearly, and SOC and particulate organic matter C (POM-C) at baseline, 5 yrs and 11 yrs later. Continuous NT depressed grain yields (10%) but not stover yields compared to ST. Continuous NT and increasing N fertilization rate increased surface (0–7.5 cm) SOC stocks 10 and 13%, respectively, compared to baseline. Seven years of ST completely negated initial surface (0–7.5 cm) SOC gain under NT and was only partially explained by POM-C loss (8–25%). All treatments lost between 14 and 19 Mg C ha−1 in the soil profile (0–120 cm) compared to baseline with no N or tillage effects. Soil C cycling appears to be rapid in this irrigated system, requiring greater C inputs to maintain SOC stocks. Effective conservation practices will need to balance crop yield, surface erosion protection, and profile-wide SOC stock losses

Response Of Irrigated Corn To Nitrogen Fertility Level Within Two Tillage Systems

Irrigated farmers generally utilize intensive tillage to manage crop residues and prepare a seedbed for com. Nitrogen fertilizer management practices have been developed for conventional-till (CT) irrigated com production. Little information is available for no-till (NT) and reduced-till (RT) irrigated com production systems. This paper compares the response of irrigated continuous com to N fertility level under CT and NT or RT production systems on a Fort Collins clay loam soil from 1999 through 2001. Grain yields increased similarly with increasing available N level [soil NO3-N (0-3 ft) plus fertilizer N added] in 1999,2000, and 2001 for both tillage systems. The CT com yields were greater than the RT or NT com yields in 1999 and 2001, respectively. Based on the results from this study, similar N levels were required. for optimum com yields in all tillage systems. Additional years of data are needed to determine if NT will require a higher level of N fertilizer input than CT to optimize com grain yields. Current N fertilizer recommendations for CT irrigated com production would appear to be adequate for irrigated NT com production

Long-term N fertilization and conservation tillage practices conserve surface but not profile SOC stocks under semi-arid irrigated corn

No tillage (NT) and N fertilization can increase surface soil organic C (SOC) stocks, but these gains are frequently not observed through the soil profile and could be subject to loss through subsequent tillage events. We evaluated a long-term irrigated continuous corn no-tillage (NT) and N rate study near Fort Collins, CO that was split into continuous NT or strip till (ST) treatments after five years. We measured grain and residue yields yearly, and SOC and particulate organic matter C (POM-C) at baseline, 5 yrs and 11 yrs later. Continuous NT depressed grain yields (10%) but not stover yields compared to ST. Continuous NT and increasing N fertilization rate increased surface (0–7.5 cm) SOC stocks 10 and 13%, respectively, compared to baseline. Seven years of ST completely negated initial surface (0–7.5 cm) SOC gain under NT and was only partially explained by POM-C loss (8–25%). All treatments lost between 14 and 19 Mg C ha−1 in the soil profile (0–120 cm) compared to baseline with no N or tillage effects. Soil C cycling appears to be rapid in this irrigated system, requiring greater C inputs to maintain SOC stocks. Effective conservation practices will need to balance crop yield, surface erosion protection, and profile-wide SOC stock losses

Nitrogen Fertilization Of Irrigated Corn In A High Residual Soil N Environment In The Arkansas River V Alley

High levels of residual soil NO3-N are present in the soils in the Arkansas River Valley where melons and other vegetable crops are produced. The amount of N fertilizer required to optimize the yield potential of crops, such as corn, following vegetables needs to evaluated to reduce NO3-N leaching potential in the Valley where high NO3-N levels have been reported in the ground water. This study evaluated the effects of N fertilizer rate (0, 50, 100, 150, 200, and 250 lb N/a) and N source (urea and Polyon®3) on corn yields following 5 years of alfalfa and one year of watermelon production. Corn grain yields were not increased by N fertilization in 2000 and were not influenced by N source. Corn plant stands were reduced by urea broadcast, incorporated application rates above 150 lb N/a in 2000, but were maintained when Polyon® was used. Silage yields increased with increasing N rate up to about 150 lb N/a, then decreased with increasing N rate. Soil residual NO3-N levels increased with increasing N rate in 2000. In 2001, corn grain and silage yields did not increase with increasing residual soil NO3-N levels (no N fertilizer applied). Based on this study, it appears that a minimal amount (\u3c50 lb N/a) of N fertilizer needs to be applied to corn to maintain grain and silage yields in the Valley in rotations with a vegetable crop like watermelon. Fertilizer N appears to be moving out of the root zone with downward movement of irrigation water

Spring Wheat Response to Tillage and Nitrogen Fertilization in Rotation with Sunflower and Winter Wheat

Spring wheat (Triticum aestivum L.) is amajor crop in the northern Great Plains that is generally grown following a 21-mo fallow period. A 12-yr study was conducted to determine the effects of tillage system [conventional-till (CT), minimum-till (MT), and no-till (NT)],N fertilizer rate (34, 67, and 101 kg N ha-1), and cultivar (Butte86 and Stoa) on spring wheat yields within a dryland spring wheat (SW)–winter wheat (WW)–sunflower (Helianthus annuus L.) (SF) rotation. Grain yield responses varied with tillage system, N fertilizer rate, cultivar, and year as indicated by significant tillage x N rate x year and N rate x cultivar x year interactions. In years with .260 mm total plant available water (TPAW) but TPAW, NT grain yields were greater than those with CT at the highest N rate, with similar trends at the medium and low N rates. When TPAW exceeded 400 mm, grain yields for CT were generally greater than for NT at the medium N rates. The greatest 12-yr average grain yield (1727 kg ha-1) was obtained with NT and application of 101 kg N ha-1. Grain yields were lowest during years when TPAW was mm, with only small responses to tillage and N treatments. Cultivars responded similarly to N fertilization in years with \u3e300 mm TPAW, with Butte86 yielding more than Stoa in 6 out of the 12 yr. Soil NO3–N levels increased in the root zone following three consecutive drought years, but had declined to initial year levels by the end of the study. These results indicate that farmers in the northern Great Plains can produce SW following SF in annual cropping systems that do not include a fallow period, particularly if NT or MT systems are used with adequate N fertilization

Spring Wheat Response to Tillage System and Nitrogen Fertilization within a Crop–Fallow System

Spring wheat (Triticum aestivum L.) production in the northern Great Plains generally utilizes conventional tillage systems. A 12-yr study evaluated the effects of tillage system [conventional-till (CT), minimum- till (MT), and no-till (NT)], N fertilizer rate (0, 22, and 45 kg N ha-1), and cultivar (Butte86 and Stoa) on spring wheat grain yields in a dryland spring wheat–fallow rotation (SW–F). Butte86 yields with CT exceeded NT yields in five out of 12 years with 0 and 22 kg N ha-1 applied, and four years with 45 kg N ha-1 applied. Stoa yields with CT exceeded NT yields in three out of 12 years with no N applied, four years with 22 kg N ha-1 applied, and only one year with 45 kg N ha-1 applied. Yields with NT exceeded those with CT in one year. Most years, yields with MT equaled those with CT. Responses to N tended to be greatest in years when spring soil NO3–N was lowest. Positive yield responses to N fertilization with CT occurred in three years with Butte86 and two years with Stoa; with MT, four years with Butte86 and two years with Stoa; and with NT, five years with Butte86 and three years with Stoa. Cultivars were not consistent in their response to tillage and N fertilization. These results indicate that farmers in the northern Great Plains can successfully produce spring wheat in a SW–F system using MT and NT systems, but yields may be slightly reduced when compared with CT systems some years

Achieving Lower Nitrogen Balance and Higher Nitrogen Recovery Efficiency Reduces Nitrous Oxide Emissions in North America's Maize Cropping Systems

Few studies have assessed the common, yet unproven, hypothesis that an increase of plant nitrogen (N) uptake and/or recovery efficiency (NRE) will reduce nitrous oxide (N2O) emission during crop production. Understanding the relationships between N2O emissions and crop N uptake and use efficiency parameters can help inform crop N management recommendations for both efficiency and environmental goals. Analyses were conducted to determine which of several commonly used crop N uptake-derived parameters related most strongly to growing season N2O emissions under varying N management practices in North American maize systems. Nitrogen uptake-derived variables included total aboveground N uptake (TNU), grain N uptake (GNU), N recovery efficiency (NRE), net N balance (NNB) in relation to GNU [NNB(GNU)] and TNU [NNB(TNU)], and surplus N (SN). The relationship between N2O and N application rate was sigmoidal with relatively small emissions for N rates <130 kg ha−1, and a sharp increase for N rates from 130 to 220 kg ha−1; on average, N2O increased linearly by about 5 g N per kg of N applied for rates up to 220 kg ha−1. Fairly strong and significant negative relationships existed between N2O and NRE when management focused on N application rate (r2 = 0.52) or rate and timing combinations (r2 = 0.65). For every percentage point increase, N2O decreased by 13 g N ha−1 in response to N rates, and by 20 g N ha−1 for NRE changes in response to rate-by-timing treatments. However, more consistent positive relationships (R2 = 0.73–0.77) existed between N2O and NNB(TNU), NNB(GNU), and SN, regardless of rate and timing of N application; on average N2O emission increased by about 5, 7, and 8 g N, respectively, per kg increase of NNB(GNU), NNB(TNU), and SN. Neither N source nor placement influenced the relationship between N2O and NRE. Overall, our analysis indicated that a careful selection of appropriate N rate applied at the right time can both increase NRE and reduce N2O. However, N2O reduction benefits of optimum N rate-by-timing practices were achieved most consistently with management systems that reduced NNB through an increase of grain N removal or total plant N uptake relative to the total fertilizer N applied to maize. Future research assessing crop or N management effects on N2O should include N uptake parameter measurements to better understand N2O emission relationships to plant NRE and N uptake

Lignin biochemistry and soil N determine crop residue decomposition and soil priming.

Not AvailableResidue lignin content and biochemistry are important properties influencing residue decom- position dynamics and native soil C loss through priming. The relative contribution of high lignin residues to soil organic matter (SOM) may be less than previously believed, be more sensitive to soil N status, and may be more sensitive to increased temperature. We examined the role of residue bio- chemistry, temperature, and soil N on the decompo- sition dynamics of five crop residues varying in lignin content and composition (corn, sorghum, soybean, sunflower and wheat). We used natural abundance d13CO2 to quantify residue decomposition and soil priming from a soil previously cropped to wheat- fallow or to corn-millet-wheat at 20 and 30 °C in a laboratory incubation. High lignin residues decom- posed more completely than low lignin residues, supporting a new model of SOM formation suggesting high lignin residues have a lower efficiency for stabilizing SOM due to inefficient microbial process- ing. However, residues with lower residue respiration had greater soil C respiration (soil priming). Residue SG lignin was positively related to residue C respired and H-lignin positively related to soil C respired in all soils and temperatures, resulting in no net lignin chemistry effect on the combined total C respired. Effects of lignin on residue decomposition were most apparent in treatments with lower soil N contents indicating N limitation. Measuring both residue and soil respiration and considering soil N status is important to accurately assess the effects of residue biochemistry on soil organic carbon.Not Availabl