Recipient Organization
UNIVERSITY OF NEBRASKA
(N/A)
LINCOLN,NE 68583
Performing Department
(N/A)
Non Technical Summary
Cover crops (CCs) are considered a leading technology to restore or maintain soil organic C(SOC) and improve soil health. However, while CCs have a potential to deliver these services,significant gaps still exist in our knowledge. Most CC studies report data on SOC and soil healthonly for shallow depths (< 30 cm), are short-term (< 10 yr), and focus on a subset of soil healthindicators. Yet, soil-profile, long-term, and comprehensive data are needed to refine ourunderstanding of CC impacts. This project is designed to fill this knowledge gap forrepresentative soils in the western Corn Belt. Specifically, it will examine the long-term (10- to15-yr) impacts of early- and late-terminated CCs on soil-profile: 1) C pools and SOCsequestration and 2) soil health indicators. Two existing 10-yr experiments with early (2-3 wkbefore planting) and late (at crop planting) CC termination in rainfed and irrigated no-tillcontinuous corn systems in the western Corn Belt will be used. We will sample soil to at least 1m to measure SOC pools, soil physical, chemical, and biological health indicators, and root CCbiomass. We will also determine aboveground CC biomass, crop yields, and other parameters.Data will be used for predicting SOC sequestration on regional scales using models (i.e., DNDC).This project is novel because no previous project has comprehensively assessed soil-profile SOCand soil health in the long term under early- and late-CC termination in rainfed and irrigatedsystems. It will thus deliver valuable data to make informed decisions.
Animal Health Component
100%
Research Effort Categories
Basic
0%
Applied
100%
Developmental
0%
Goals / Objectives
Long-Term Goal The long-term goal of this project is to promote C maintenance or sequestration and improvement in the health of agricultural soils by using improved cover crop (CC) management practices in rainfed and irrigated no-till systems in the Corn Belt and western Corn Belt in particular.Specific Objectives Evaluate the long-term (10- to 14-yr) impacts of early- and late-terminated CCs on soil-profile C sequestration and C pools in rainfed and irrigated no-till continuous corn to at least 1 m soil depth in the western Corn Belt.Assess the long-term (10- to 14-yr) impacts of early- and late-terminated CCs on soil health indicators (physical, chemical, and biological properties) at different soil depth intervals to at least 1 m depth in rainfed and irrigated no-till continuous corn in the western Corn Belt.Use process-based models to extrapolate the effects of CCs on soil C sequestration and soil properties to regional scales.HypothesesEarly- and late-terminated CCs will sequester C and increase C pools in the whole soil profile relative to no CCs, but late-terminated CCs will accumulate more soil C than early-terminated CCs due to increased CC biomass production.Early- and late-terminated CCs will enhance no-till potential to improve soil health not only in the surface (< 30 cm) but also in the subsoil (> 30 to 100 cm).Process-based models can satisfactorily estimate soil C stocks and C pools under different CC management practices (early vs. late) on regional scales.
Project Methods
MethodsWe will use two existing study sites in Nebraska: 1) University of Nebraska-Lincoln's (UNL) Rogers Memorial Farm (RMF) near Eagle, NE and 2) UNL's South Central Agricultural Laboratory (SCAL) near Clay Center, Nebraska. The 30-yr precipitation is 818 mm at RMF and 688 mm at SCAL while 30-yr mean annual temperatures are 10 °C at RMF and 13 °C at SCAL. The RMF site is rainfed while SCAL is irrigated and both are under no-till continuous corn.The experiments at these two sites were established in fall 2013 with treatments of no cover crop (CC), an early-terminated cereal rye CC, and a late-terminated cereal rye CC. The early-terminated CC is terminated about 2-3 weeks before corn planting while the late-terminated CC is terminated at the time of corn planting. The treatments are arranged in a randomized complete block with four replications at each site. Thus, at each site there are 12 plots. Plot size is 10 m by 10 m at RMF and 10 m by 7.5 m SCAL, with each plot containing 12 corn rows. Note that CCs are never irrigated.Soil Sampling:Soil will be sampled to assess total SOC, C pools, and soil health indicators to depths of 0-5, 5-10, 10-20, 20-30, 30-40, 40-60, 60-80, 80-100, 100-150, and 150-200 cm in spring just before corn planting in all years of the current proposal using a Giddings hydraulic truck-mounted probe. We will collect 6 samples per plot and composite by depth for soil analyses. Note that we will assess all soil health indicators in years 1, 3, and 5 and total C and C pools (Objective 1) in all years. This sampling scheme will provide detailed data for modeling purposes.Plant Sampling and Analysis:Cover crop aboveground biomass will be sampled at each CC termination date. Two 0.25 m2 quadrats will be collected per plot. We will collect 4 soil cores with the Giddings hydraulic truck-mounted probe for the analysis of roots. Roots will be separated from soil using a hydropneumatic elutriation system. Both aboveground biomass and washed roots will be dried at 60 °C for 3 days, weighed, and ground for further analysis. Both aboveground biomass and roots will be analyzed for C concentration by dry combustion. Corn residue amount and grain yield will be determined in fall at harvest to assess the impacts of CC termination date on the main crop.Soil-Profile C Sequestration and C PoolsObjective 1: Evaluate the long-term (10- to 14-yr) impacts of early- and late-terminated CCs on soil-profile C sequestration and C pools in rainfed and irrigated no-till continuous corn systems to at least 1 m soil depth in the western Corn Belt.Using the composited samples from the 0-5, 5-10, 10-20, 20-30, 30-40, 40-60, 60-80, 80-100, 100-150, and 150-200 cm depths collected as described above, we will determine total SOC, particulate C, and mineral-associated C from both sites in all years. Total SOC will be determined on air-dry, finely ground soil by dry combustion. To determine particulate C and mineral-associated C, we will combine 30 g of air-dried soil with a 5% sodium hexametaphosphate (HMP) solution to disperse soil aggregates. The sample plus HMP solution will be shaken on a reciprocal shaker for 24 hrs. The dispersed sample will then be sieved through a 53 µm sieve with vessel below to catch the silt+clay fraction. The contents of the 53 µm sieve will then be transferred to a tin pan and dried at 60 ºC and weighed.Soil C stocks will be determined from SOC concentration and soil bulk density data. To compute SOC sequestration, we will compute the difference in SOC stocks at the start of the experiment from SOC stocks at 10 yr and onwards divided by the number of years under CCs.Soil-Profile Changes in Soil Health Indicators Objective 2: Assess the long-term (10- to 14-yr) impacts of early- and late-terminated CCs on soil health indicators (physical, chemical, and biological properties) at different soil depth intervals to at least 1 m depth in rainfed and irrigated no-till continuous corn systems in the western Corn Belt.We will measure a suite of soil physical, chemical, and biological properties as indicators of soil health in years 1, 3, and 5 from all soil depths collected above. In-field tests of water infiltration and penetration resistance will include 2 and 10 sampling locations per plot, respectively. Water infiltration will be assessed using a double ring infiltrometer in each plot for 3 h (until steady state) with readings at 0, 1, 2, 3, 4, 5, 10, 30, 60, 90, 120, 150, and 180 min after addition of water. Penetration resistance will be measured at depths of 0-5, 5-10, 10-20, 20-30, and 30-40 cm.Laboratory-based tests on the composited bulk samples and soil cores include soil texture, wet-aggregate stability, bulk density, and plant available water. Soil texture will be assessed using the hydrometer method and wet-aggregate stability by the wet-sieving method. From the air-dried composite sample, we will also analyze the samples for soil chemical properties of pH, electrical conductivity, and soil nutrients (NO3-, P, K, Ca, Mg, Na, S, and micronutrients). Note that we will also have organic C, total N, and particulate organic C from Objective 1 to complement the suite of soil chemical data. Potentially mineralizable N will be assessed using a short-term anaerobic incubation and potentially mineralizable C through a short-term aerobic incubation. Note that potentially mineralizable C and N are additional indicators of labile organic matter and biological activity.Bulk density and plant available water will be analyzed from the intact soil cores. We will determine water retention at -0.033 MPa (field capacity) and -1.5 MPa (permanent wilting point) matric potentials. Plant available water will be computed as the difference in volumetric water content at -0.033 and -1.5 MPa matric potentials. The total plant available water for the soil profile will then be computed.Soil fungal and bacterial communities will be quantified using fatty acid methyl ester (FAME) profiling to complement the above-mentioned physical and biochemical measurements. Fungal biomass will be measured using the AMF-specific fatty acid biomarker C16:1cis11 and saprophytic fungal marker C18:2cis9,12.Soil C ModelingObjective 3: Use process-based models to extrapolate the effects of CCs on soil C sequestration and soil properties to regional scales.We will test the DNDC model to simulate C dynamics for our project. The DNDC model is a biogeochemical model with inputs of climate, soil properties, and crop production and practices. The Canadian version (DNDCv.CAN) assumes a heterogeneous soil profile and simulates C dynamics to 2 m. This is in contrast to the standard version, which assumes a homogenous soil profile to 0.5 m. We will use our soils data collected in Objective 2 to parameterize the model, while data from Objective 1 will be used to calibrate and validate the model. We will use data on management, soils, climate, and others for building model files. Because a major limiting factor for the use of current C is the lack of measured data, we will, in this project, collect data on soil properties, soil moisture, total soil C, labile C, aboveground CC biomass, belowground (root) CC biomass, and others from Objectives 1 and 2. Cover crop biomass production data used will be used as input.We will revise the functions of DNDC and introduce any new functions to simulate soil process associated with C sequestration and dynamics. We will develop an improved model to predict C sequestration and dynamics to optimize CC management. The DNDC model was developed, parameterized, and validated based on traditional farming practices. When CCs are added, rates of organic matter decomposition and inputs change along soil physical, chemical, and microbial properties leading to unprecedented new conditions.