Cover crop selection and manure placement for weed suppression and nitrogen use efficiency in a no-till organic corn system
The long-term profitability and sustainability of organic corn (Zea mays L.) production must include reliable weed and fertility management strategies that minimize production costs, conserve soil, and maximize nutrient use efficiency. This may be accomplished through integration of novel manure subsurface banding technologies with an optimal legume/grass cover crop mixture and supplemental high-residue cultivation. The specific goals of this graduate student project are to 1) determine C and N release and persistence of decomposing cover crop surface mulches that vary in grass:legume proportions; 2) evaluate the effect of poultry litter placement on soil N spatial and temporal availability; and 3) determine the cover crop combination and poultry litter placement that optimizes N availability and corn N use efficiency. A field experiment was conducted beginning fall 2010 for preliminary data collection and methods development; samples collected during the 2011 field season are now being processed for analysis. To address the research objectives, a collaborative field experiment was established in fall 2011, with a range of rye: hairy vetch cover crop mixtures planted and baseline soil samples collected.
1. Cover crop residue decomposition
a. Characterize C and N dynamics over time in decomposing cover crop residues composed of a range of legume:grass proportions to determine the mixture that results in the longest-lasting cover for weed suppression
b. Determine the effect of poultry litter application (0 v. 67 kg plant available N ha-1), poultry litter placement (broadcast v. subsurface banded) and tillage on the rate of residue decomposition and N release for residues of varying composition
-Cover crop mixtures were established in two fields in fall 2011 totaling six replicates
-Litter bags were placed in the field during the 2011 field season; the litter bag contents were dried and ground this fall
2. Soil N
a. Characterize the spatial distribution of soil N in subsurface banded and broadcast poultry litter treatments across a gradient of cover crop mixtures and over time
-During the 2011 field season, spatial measurements of pH, electrical conductivity and nitrate were taken in exposed soil faces at three corn development stages after sidedressing in the subsurface banded and no poultry litter treatments
-Spatially-specific soil cores were collected in subsurface banded and no poultry litter treatments and have been ground in preparation for analysis
b. Determine the effect of high-residue cultivation on N distribution in subsurface banded and no-till broadcast poultry litter treatments
3. Crop and weed N uptake
a. Determine the efficiency at which N is taken up and the relative sufficiency of N for corn growth in no-till plots receiving subsurface banded, broadcast and no poultry litter, as well as in tillage plots receiving incorporated poultry litter with varying cover crop proportions
-During the 2011 field season, corn, weed and soil samples were collected at several corn growth stages to assess N pools; plant samples have been dried, weighed and ground and soil samples have been ground in preparation for analysis
-Bare soil plots were established within the experiment to serve as a check plot for background soil N mineralization needed to calculate N uptake efficiency next season
The summer of 2011 served as an opportunity for me to become familiar with the larger organic rotational no-till systems trial, and to develop methods to use in my research over the next two years. The experiment was set up in fall of 2010 without my direct involvement, and I began preliminary data collection in spring 2011 once my research plans had been made. Only costs associated with this preliminary work incurred after July 25 will be applied to the grant.
In fall 2010, two fields located on Beltsville Agricultural Research Center North Farm and South Farm, were planted with a range of hairy vetch (Vicia villosa Roth): triticale (Triticale hexaploide Lart.) mixtures (0:1, 0.2:0.8, 0.4:0.6, 0.6:0.4, 0.8:0.2, 1:0) for a total of three experiment replicates (two on South Farm, one on North Farm). Each of the replicates had plots 6.1 x 12.2 meters in size. However, problems during cover crop planting led to incorrect mixture compositions in several plots in the South Farm field. In response, the plots on the North Farm experiment were halved, creating an extra rep. Cover crop biomass was collected in three ½ m2 quadrats in each mixture at North Farm and in two ½ m2 quadrat per mixture at South Farm just prior to cover crop termination. Fertility treatments included broadcast and incorporated pelletized poultry litter applied at a rate of 3.4 Mg ha-1 and subsurface banded poultry litter at rates of 0, 3.4 and 6.7 Mg ha-1. A no-starter fertilizer treatment was also included.
On May 23, cover crops in the no-till treatments were rolled and corn was planted at a rate of 89,000 seeds ha-1 with 76 cm rows (53R57 Blue River hybrids, 104 day). All plots except the no-starter plots received starter fertilizer at a rate of 1.42 kg poultry litter per 30.5 m of row. The North Farm no-till treatments had been rolled 11 days prior to the final rolling and planting, and in the tillage treatments, cover crop residues were mowed and incorporated 11 days prior to planting. Poultry litter was broadcast just prior to planting, and incorporated in the tillage plots with a cultimulcher. Vetch was at 20% flowering and the triticale was 70 on Zadok’s scale (just after anthesis). We noticed vetch and triticale regrowth, but triticale regrowth was only in the 100% triticale treatments. The no-till plots were re-rolled on June 1. Corn emergence was somewhat spotty, probably because some of the corn seeds were not placed in the furrow properly at planting, but perhaps also due to inadequate furrow closure, desiccation and insect herbivory.
Three rotary hoe operations took place in the tillage treatments between May 27 and June 2, followed by two between-row cultivations (first with shield, second without shield) on June 14 and June 23. High residue cultivation in the no-till plots took place on June 23 and June 30. Sidedressed poultry litter was hand-applied on July 6 and 7, when corn was in the V6 growth stage. Delays in calibrating the subsurface banding applicator precluded us from subsurface banding the poultry litter before it was too tall. The corn was harvested by combine on October 10 (South Farm) and October 17 (North Farm).
Litter bags were placed in both fields and collected throughout the season to characterize mixture decomposition and test different litter bag methods. The North Farm litter bags were filled with hairy vetch and triticale at vetch:triticale proportions of 1:0, 0.75:25, 0.5:0.5, 0.25:0.75 and 0:1 for field target mixtures of 1:0, 0.8:0.2, 0.6:0.4, 0.2:0.8 and 0:1. Fresh cover crop biomass collected from border areas was placed in 30 x 30 cm 1-mm mesh bags assuming total biomass of 6725 kg ha-1 and moisture contents of 70% for vetch and 56% for triticale, based on measured moisture contents of these species at similar growth stages in other experiments. Biomass in bags dried immediately after filling revealed that the moisture content assumptions were too low: actual moisture content of the vetch was 87% and that of the triticale was 81%. This inaccurate assumption caused the litter bag contents to represent biomass levels of ~3040 kg ha-1 and 3050 kg ha-1 for vetch and triticale, respectively. Thus, although our biomass estimate for the field was in the range of actual field biomass levels, the moisture content assumptions caused litter bag contents to be approximately half the field biomass levels. The residues were cut to fit in the bag, and poultry litter was included at a rate representing the field rate in the broadcast treatment (the soil surface at the location of litter bags was blocked from broadcasted litter). The bags were placed on the soil surface in the 3.4 Mg ha-1 broadcast and 0 Mg ha-1 treatments, at three different interrow locations in a single cover crop mixture in the 3.4 Mg ha-1 subsurface banded treatment and buried in three cover crop mixtures in the tillage treatment (0:1, 0.4:0.6 and 1:0 vetch:triticale mixtures). The bags were placed in the field at the first rolling (11 days before planting). Bags in the tillage treatment were buried at a downward angle to 20 cm. In the no-till plots, existing residue was cut to make a mulch-free spot for the litter bags. All bags were placed ~2.5 cm next to the corn row and starter fertilizer band, except the ones in the 3.4 Mg ha-1 subsurface banded treatment, which were placed either next to the row, between the row and interrow center or in the interrow center.
The South Farm litter bags were filled according to the South Farm cover crop biomass and moisture content data. For these litter bags, residue was air dried in the greenhouse prior to filling the bags. Litter bags were placed in three cover crop mixtures (0:1, 0.4:0.6 and 1:0 vetch:triticale) in the 0 Mg ha-1 treatment, and only in the 0.4:0.6 mixture of the tillage treatment. Also, 2 mm mesh bags with air dry residue and 1 mm mesh bags with fresh residue were placed in the 0 Mg ha-1 40:60 vetch:triticale treatment. Biomass levels of 4000 kg ha-1 and 6000 kg ha-1 were targeted in the 100% vetch and 100% triticale bags, respectively, and an average rate of 4290 kg ha-1 and 6130 kg ha-1 went into these bags. The target biomass levels were based on the dry weight of biomass collected in the South Farm mixtures. Because there weren’t replicates at the South Farm, two sets of litter bags were placed in each replicate. The litter bags were placed in the field four days after planting. Locations of bags in the interrow and depth of burial were the same as on North Farm.
One set of litter bags was collected on the day of litter bag filling, and another set at each of the following corn growth stages: V2, V5, R1 and R6. The collection dates for the two fields remained offset by ~2 weeks throughout the experiment, except for at the R6 sampling. Throughout the season, the bags were removed for field operations and replaced to their original locations after each operation. When a set of litter bags was removed for sampling, mulch from the surrounding area within the plot was spread over the location of the collected bags. At each sampling, the collected litter bags were examined for weeds growing into the bags, and in such cases the weeds were carefully removed. The bags were placed in the dryer at 60°C for two weeks. Then, the litter bag contents were weighed and ground twice to pass a 1 mm sieve. This fall, litter bag subsamples were ashed to determine the proportion of soil contamination on the residues. Next, the samples will be analyzed for C and N and subjected to microbial experiments by a collaborator.
Soil N dynamics
Soil samples were collected over the season to evaluate treatment effects on soil N over time. Eight 2.5-cm soil cores from 0 to 30 cm were composited per plot at emergence, V2, V5 and R6 growth stages. At the first three sampling events (prior to sidedress fertilizer application), samples were collected in the tillage, broadcast and 0 Mg ha-1 subsurface banded treatments. At the R6 sampling, all fertility treatments were sampled in a subset of mixtures. The soil samples were sieved through a 6.35 mm sieve, set out to air dry and placed in storage prior to grinding, homogenizing, extracting with 1 M KCl and analyzing for inorganic N.
In addition to the soil cores, intensive soil sampling and field measurements were performed on 4.5 Mg ha-1 subsurface banded and 0 Mg ha-1 subsurface banded plots in a separate organic no-till corn experiment. Three soil pits were sampled in each of the subsurface banded and no sidedress treatments at three times: at V5, R1 and R6 growth stages. At each sampling event, spatially-specific soil cores were taken surrounding the proposed soil pit location. Seven evenly-spaced locations across the interrow (perpendicular to the corn row), including within the corn rows were sampled. The center sampling point was lined up with the poultry litter band, which was found by exposing a soil face near the pit location. Each core was split into 10-cm segments (0-10, 10-20, 20-30 cm depth). Four parallel lines, approximately 15 cm apart were sampled in this way. Cores from symmetric locations on either side of the interrow center were composited, as were cores from matching locations in the four parallel sampling lines. After the intensive core sampling, pits were dug 76 cm wide and 30 cm deep. A plexiglass grid, 34 cm across with holes every 5 cm across and deep was placed in the pit so that the first core holes were located on the poultry litter band. Volumetric water content readings were taken from halfway between the row and interrow center, at 2, 12 and 22 cm depth. Then, the soil face was sprayed with water and electrical conductivity (EC) and pH readings were taken in a subset of grid holes. Soil cores were taken out of the same holes and mixed with distilled water to form a 1:1 slurry. The slurries were allowed to settle for a few minutes before placing a sample on the nitrate meter. Generally, the field instruments worked well, but accuracy of the nitrate meter seemed to deteriorate by the end of sampling at the R6 stage. Soil cores were taken from a subset of the measured grid holes for lab N analysis. After sampling, a fresh face was exposed in a subsurface banded and no sidedress pit for colorimetric pH. To do this, the soil faces were sprayed with water, sprayed with triplex pH indicator, covered with barium sulfate powder, then photographed. The vertical soil cores and soil face cores have been sieved and air-dried, but not analyzed.
Crop N status and weed sampling
A random sample of corn shoots was collected at the V2, V5 and R6 growth stages from the plots that were soil sampled. Weeds were also collected in 1 m2 quadrats (0.76 m wide x 1.3 m parallel to rows) at the V5 and R1 growth stages. At the V5 sampling, weeds were collected in the same plots sampled for shoot biomass and soil. At the R1 sampling, all plots were sampled for weeds. The shoot biomass has been dried, weighed and ground in preparation for C and N analysis.
In fall 2011, the field experiment was set up on two new fields at the Beltsville Agricultural Research Center (North Farm- fine loamy, mixed, mesic Typic Endoaquult and South Farm- fine loamy, mixed, mesic Typic Dystrudept). The fields had been in forage soybeans without prior N application and were moldboard plowed, disked twice, field cultivated using an S-tine harrow and cultimulched prior to cover crop planting. Three reps were planted on each field, totaling six reps with plots 6.1 x 12.2 m in size with 3.05-m alleys between reps and a border area of at least 3.05 m around all sides. Cover crops were planted in hairy vetch: cereal rye (Secale cereale L.) mixtures of 0:1, 0.2:0.8, 0.4:0.6, 0.6:0.4, 0.8:0.2, 1:0 arranged randomly within reps, with the full rate of hairy vetch equal to 34 kg ha-1 and that of cereal rye equal to 168 kg ha-1. The fields were planted with a 10-foot drill on October 7 (North Farm) and October 10 (South Farm). Visual geese deterrents were placed on the South Farm field to prevent geese damage to the cover crops. In November, alleys were field cultivated in the direction of future corn planting to establish bare check plots. The N taken up by corn in these plots will represent plant available N provided by the soil without fertilizer amendment. Twenty 0-30 cm soil cores, spatially distributed in a random pattern, were collected within each rep on November 21, 2011 for baseline soil characterization.
During the summer and fall of 2011, preliminary data were collected in the previous field experiment and samples were processed in preparation for analysis, which will occur this winter. Experience from last summer taught us to plant extra replicates of cover crop mixtures to ensure a fully replicated experiment in case of problems with cover crop planting or establishment. Next spring, cover crop biomass will be collected approximately one week prior to setting out the litter bags (for example at first rolling, and litter bags set out at second rolling/planting) so that more accurate cover crop biomass, mixture proportions and moisture content estimates can be used to inform litter bag contents. Also next year, the subsurface banding applicator will be calibrated well before the V5 growth stage so that the poultry litter will not need to be hand-applied. In addition to collecting preliminary data, this fall the 2011/2012 experiment was set up (cover crops planted, check plots cultivated) and baseline soil samples collected.
Impacts and Contributions/Outcomes
My graduate research project is just getting started and has not yet achieved large impacts and contributions. However, presentation of my proposed research to the Environmental Science and Technology department this fall provided an opportunity to share my proposed research and expected outcomes with other researchers, which created interest in organic no-till crop production and provided an opportunity to gain feedback on my research plan. I have also described my project plan informally to farmer friends as well as other sustainable agriculture researchers and nutrient management planners, who have shown interest and provided input on the project. After I compile preliminary data this winter, I will present these exploratory results with other soil scientists at a departmental research meeting. I look forward to including my research results in field days, webinars and presentations once I have generated more data.
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