Sustainable cropping systems for dairy farmers in the Northeast, II

Weather

Weather conditions over the past seven years provided a range of opportunities to assess cropping system performance. Rainy fall (2011, 2012) and spring (2011, 2012) conditions had high slug density activity and years with dry mid-summer weather (2011, 2012, and 2016) had some reduction of corn and perennial forage crop production (Figure 1). With unusually warm early spring temperatures in 2012, 2015, and 2016 (Figure 2), canola flowered early and during the unusually cold winter with limited snow cover of 2014, winter canola and crimson clover died. Compared to 2015, 2016 was a drier growing season (Figure 1). In spite of higher rainfall in May 2016 (3.43 inches) compared to 2015 (1.37 inches), precipitation totaled 6.46 inches during the months of June and July in 2016, whereas it totaled 12.87 during the same period of time in 2015. Despite 2016 being a drier year compared to 2014 and 2015, we did not observe drastic yield losses compared to the previous years (Table 1 & 4).

figures 1-2

Manure Rotation: Yields  

With the exception of the second year alfalfa stand yield in 2016, crop yields were similar between the broadcast and inject manure treatments (Table 1). The alfalfa yield was 15.6% higher in the BM treatment (the variety without leafhopper resistance) compared to the IM treatment which was the leafhopper resistant variety (17.2 and 15.6 Mg ha^-1, respectively) suggesting the possibility of the resistance trait contributing to a yield drag. In contrast to 2015, the crop × manure management interaction effect on crops yield was not significant in 2016. Corn silage yields in manure rotation were slightly lower in 2016 compared to 2015 which could probably be explained by lower rainfall in the months of June and July in 2016 compared to the same time period in 2015.

Table 1

Lysimeter plots

PhD student Emily Duncan successfully defended her dissertation in May, 2016, completing four studies:

Study 1: Development and hydrologic evaluation of the plot scale lysimeters were described. Because variability in quantities of both surface and subsurface nutrient loading varied among plots, multi-year data on water flow from each plots was compared and revised treatment blocking pairing were recommended (See the outreach for the related publication).

Study 2: Manure injection (shallow disk) was shown to greatly reduce ammonia emission (>90%), but to significantly increase direct emissions of nitrous oxide (up to 150%), compared to unincorporated applications of dairy manure. While the increased N loss as nitrous oxide offsets only a small fraction on the N conserved by reducing ammonia emission, the impact of the nitrous oxide as a greenhouse gas must be considered when evaluating the overall benefit of manure injection (See the outreach for the related publication).

Study 3: The entire N balance was compared between shallow disk injection and unincorporated, broadcast application of dairy slurry. Greatly decreased ammonia losses with injected had the greatest impact on the N balance.  No significant differences in N losses to either surface or subsurface were seen between manure application treatments.  Despite greater conservation of manure N with injection, no significant differences in corn silage yield were observed.  However, greater concentrations of late season stalk nitrate in injected plots suggested that yields could have been maintained with less N when manure was injected. Manuscript to be submitted to a journal this month.

Study 4: The Integrated Farming Systems model was used to simulate dairy manure management scenarios, including application method (injection vs. broadcast) and storage capacity.  Expanding manure storage to 12 months and injecting minimized nitrate leaching losses, but cost of construction of 12 month manure storage capacity greatly reduced net returns for the farm. Injection of manure with 6 months of storage appeared to provide the best balance between economic return and environmental protection.

Lysimeter Phosphorus analysis for 2012-2015

The effect of sampling date was always significant in both overland and subsurface phosphorus losses in all of the years (Figures 3 & 4). The main effect of treatments (manure application methods) was significant in the overland loss (2014) and also in the subsurface loss (2015) with the broadcast having more P loss compared with the injection. On most of the occasions, significant P loss were typically observed after rainfall events or after manure application followed by a rainfall (Figure 3). On a few occasions, manure injection resulted in a higher P loss compared with broadcast [1/31/13 and 3/13/15 in the overland loss (Figure 3) and 6/4/12 in subsurface loss (Figure 4)]. Despite significant higher P losses in the broadcast or injection treatments in some sampling dates (Figures 3 & 4), the differences between treatments were not significant in each year. Large spikes in both overland and subsurface P losses occurred and were associated with either rainfall or manure application followed by a rainfall.

When total annual P l loss was calculated and analyzed, using “year” as the repeated measure component of the analysis, BM and IM treatments did not differ significantly; years, however, differed significantly which could presumably be explained by annual rainfall differences during this study (Figure 5). The Karst topography of the experimental site (characterized by underground drainage systems with sinkholes and cracks) and hydrologic variability of the plots likely explain some of the inconsistence differences between the broadcast and injection methods in both overland and subsurface losses. In addition, since manure was only applied once a year in 2013, 2014, and 2015, manure and soil P levels may not have been high enough to result in consistent loss or differences that could be detected with high variability hydrologic conditions. These results support the Emily Duncan research on the hydrology of the plots that indicated the current treatment pairing and current blocking based on landscape position is not representative of hydrologic similarities and should be re-assigned to new treatment pairs and new blocks to reflect similarity in historical subsurface and overland flows.

When annual overland and subsurface P losses were summed, as shown in figure 6, it was only in 2014 that broadcast manure had significantly higher total P loss then inject manure. Increased P losses after three years of manure application in 2014 may be due to higher precipitation events that contributed to high P loss in that year.

figures 3-6

Factors contributing to nitrous oxide emissions from corn fields in no-till dairy crop rotations

Nitrous oxide (N₂O) is a potent greenhouse gas released from agricultural soils primarily as a by-product of the microbial process of nitrification and denitrification. Traditional corn and soybean productions systems rely heavily on N inputs from inorganic fertilizers and account for the highest N₂O emissions among major cropping systems in the US (Del Grosso et al., 2005). To better manage the sustainability of the cropping system, legume crops can be included into corn systems to reduce inorganic fertilizer use, and manure can be used to replace inorganic fertilizer. However, the efficacy of these approaches to reducing N₂O emissions is uncertain because of the interaction of multiple factors that regulate several different N₂O producing processes in soil (Venterea et al., 2012). Research has typically been limited to studying the effect of one or two sources of N inputs on N₂O emissions from an individual system; however, systems of interest often have more than two sources and factors that may interact with each other. This study investigated how different cropping practices that include differences in crop residues, N inputs (dairy manure and inorganic fertilizer), fallow period, timing of N amendment applications and environmental conditions influence N₂O emissions from no-till soil planted to corn.

N₂O Emission Research Conclusions

Nitrogen source effect on soil N₂O emissions

In 2015, elevated N₂O emissions were observed from the legume treatments about 15 days after the previous crops were terminated and spring manure was applied (Figure 9). During this period, daily mean fluxes in alfalfa + orchard grass and crimson clover treatments varied from 2.26 to 50.86 kg N-N₂O ha^-1 d^-1   and 1.17 to 101.07 kg N-N₂O ha^-1 d^-1, respectively. By 45 days after the cover crops were terminated and manure was applied, the emissions were lower, varying in the alfalfa + orchardgrass treatment from -0.01 to 7.26 kg N-N₂O ha^-1 d^-1 and in the crimson clover from 0.09 to 6.35 kg N-N₂O ha^-1 d^-1. As in 2015, elevated N₂O emissions were found 15 days after the previous crops were terminated and spring manure was applied in 2016 (Figure 10). In 2016, peaks in May happened more often than in 2015, most likely in response to the higher amount of precipitation. In 2016, daily mean fluxes in alfalfa + orchard grass and crimson clover treatments varied from 16.8 to 72.1 kg N-N₂O ha^-1 d^-1 and 15.0 to 70.1 kg N-N₂O ha^-1 d^-1, respectively. Nitrogen input from symbiotic N fixation from the legumes, manure and weather conditions favored denitrification early in the season. Nitrate and NH₄⁺ soil levels increased slowly early in spring after manure was applied and cover crops were terminated (Figures 7 & 8). In 2015 and 2016, based on pre-side dress nitrate tests, the legume treatments did not need supplemental application of inorganic fertilizer later in the season, whereas, the broadcast manure treatment needed inorganic fertilizer to achieve the corn crop yield goals. In 2015, high emissions occurred from the soybean with broadcast manure treatment early in the spring after manure was applied and later in the season when inorganic fertilizer was applied. In contrast in 2016, emissions in the broadcast manure treatment were low early in the season and also after inorganic fertilizer application. Emissions in response to inorganic fertilizer application in the soybean with broadcast manure treatment varied between the years likely because in 2015, inorganic fertilizer application coincided with a heavy rainfall.  

Method of manure application and soil N₂O emissions

Unincorporated, broadcast manure application covered the soil surface, whereas injecting manure with the shallow disk injector left minimal manure on the soil surface. In 2015 and 2016, N₂O emissions from the soybean treatment with injected manure were elevated compared to the broadcast treatment, and UAN treatment with daily mean fluxes in 2015 that varied from 0.6 to 420.6 kg N-N₂O ha^-1 d^-1, and in 2016 from 0.3 to 121.96 kg N-N₂O ha^-1 d^-1 (Figure 9). The higher emissions in this treatment were likely because manure injection created a 10 cm deep band of concentrated N, high moisture and organic matter, which favored the process of denitrification. In 2015, the soybean with broadcast manure treatment had elevated emissions 15 days after manure application. In contrast, emissions remained low early in the season in 2016. Based on pre-side dress nitrate tests, the injected manure treatment did not need supplemental application of inorganic fertilizer later in the season, whereas, the broadcast manure treatment needed inorganic fertilizer to achieve the corn crop yield goals. This is likely because injected manure conserved more ammonical N and less was lost. In 2015, 4 days after inorganic fertilizer application N₂O emissions in the soybean with broadcast manure and UAN treatment was significantly higher compared to the soybean with injected manure. Nitrous oxide emissions were likely favored by precipitation events that happened after UAN application. In 2015, large N₂O emissions shortly after mid-season, side-dress inorganic fertilizer application likely resulted from precipitation events that created conditions favorable for denitrification (Figure 9). In 2016, a dry period after inorganic fertilizer application limited the denitrification potential and overall N₂O emissions (Figure 10).

Cumulative N₂O emissions per unit N applied

In 2015 and 2016, corn with injected manure had significantly higher potential for N₂O emissions than corn with inorganic fertilizer (Table 2). Cumulative N₂O emission per unit of N applied in the corn with injected and broadcast manure was higher than corn with inorganic fertilizer treatment. In both years, cumulative N₂O emission per unit of N applied from treatments with winter crop residues with manure and with no winter crop residues and manure, were not significantly different. In 2015 and 2016, the UAN treatment had the lowest N₂O cumulative emission per unit grain yield and per unit N applied.

Grain yield

In 2015, average grain yield was 9.2 Mg ha^-1 and was not significantly different among the treatments that received organic N inputs from manure and/or crop residues (Table 2). In contrast, in 2016 grain yields averaged was 10.5 Mg ha^-1 and was significantly lower in the alfalfa and orchargdrass treatment compared to the crimson clover treatment. In 2015 and 2016, N₂O emissions per unit of grain yields were significantly lower in the soybean with fertilizer treatment compare to the soybean with injected manure. Integration of legumes and grasses in the cropping did not reduce N₂O emissions per unit of grain yield relative to the soybean with inorganic fertilizer treatment.

Main drivers contributing to N₂O fluxes

The random forest analysis explained 48.07 % of variation in N₂O emissions. Days after manure application was identified as the most important variable, followed by days after previous crop termination, soil nitrate levels and soil moisture (Figure 11). These results suggest that timing of manure application and crop residue termination with crop uptake is critical to reduce N₂O emissions.

figures 7-11

Table 2

Conclusion

Crop rotations, organic fertilizer application, increasing plant residue are some of the practices that have the potential to increase the sustainability of crop production. Integration of legumes and grasses in these cropping systems contributed to meet yield goals and reduced the use of inorganic fertilizer, however they did not reduce direct N₂O emissions. Elevated soil N₂O emissions were observed between 15-42 days after previous crops termination and spring manure application. Although manure injection has many benefits that include reducing soil disturbance, reducing ammonia losses, phosphorus runoff, and conserving manure nutrients, we observed higher N₂O emissions in 2015 and 2016 compared to surface application with manure or inorganic fertilizer. More N was conserved when manure was injected and no supplemental inorganic fertilizer was added to meet yield goals, but the higher N availability and carbon concentration in the 10 cm injection band likely favored N₂O production by denitrification. To account for various factors driving N₂O emissions, we used Random Forest analysis. The variables included explained about 48% of the variability in the N₂O emissions. Time after manure application, days after previous crop residue termination, soil nitrate, and moisture were identified as the main measured variables driving N₂O emissions. These results suggest that to reduce N₂O emissions, N application events should be synchronized with plant N demand, managers should avoid applying N when there is a high chance of precipitation and apply an N rate based on soil N availability and yield goals.

2016 Soil Carbon Results

Following the spring tillage in the canola crop entry (Pest rotation) in August, in the top 5cm of soil in the no-till plots (SH) had 35% more soil carbon compared to those that were tilled to terminate alfalfa (RH treatment) (Figure 14).  By contrast, the tillage treatment had higher soil C at 5-15 cm soil depth compared to the no-till treatment (1.4 vs 1.2%), which could be due to the moldboard plow burying the alfalfa to this deeper soil level where it is more protected from decomposition. Soil carbon levels were also higher in the 0-5 cm depth in the no-till treatments compared to the tilled treatments in the soybean crop entry, two years after tillage (Figure 15).   Further, in the corn in the Pest rotation, three years after tillage was applied, no till plots tended to have higher C from depth of 0-5cm compared to the tillage treatment (1.8 vs. 1.4% respectively); however, the difference between tillage and no-till treatments was not significant in the soil 5-15 cm soil depth (Figure 16). 

Soil carbon levels did not significantly differ between IM and BM treatments across all of the crop entries in the manure rotation in the top 5cm of soil (1.9 vs 1.8%, respectively) or the 5-15 soil depth (1.4 vs 1.3%, respectively). In the corn-soy rotation (Control), soil C levels in the corn in the three nutrient treatments (FERT, IM, and BM) also did not differ at both soil depths (0-5 and 5-15cm) (Figure 13).  

When all crop entries from each rotation were averaged and compared across rotations, the manure rotation had 15 and 18% more soil carbon at 0-5 cm soil depth compared to the pest and control rotations, respectively. The Pest and Control rotations did not differ significantly (Figure 12).  Although the manure and pest rotations both include perennials and cover crops, there are likely a number of explanations for why soil C in corn did not differ between the pest and control rotations. As illustrated in Fig 16, in the pest rotation half of the corn entry plots had been tilled three years prior to terminate alfalfa without an herbicide (RH treatment). In addition, in the corn-soy rotation, corn is harvested for grain and the corn stalks are left in the field every other year in the corn-soy rotation contributing significant amounts of corn stalk residue to the top soil layer. By contrast, in the pest rotation, the cover crop after soybean is short-lived, and corn grain was grown in the only corn entry in the six-year rotation until 2012, but the corn stalks were removed for bedding.  Since 2013, the corn entry in the pest rotation has been corn silage.

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Fall Manure Nutrient Conservation- Satellite Experiment

Although the potential for nutrient loss and water quality impairment is higher when manure is applied in the fall rather than in the spring, limited manure storage drives the decision of northeastern dairy farmers to spread manure in the fall. This study was conducted to evaluate three field management strategies: i) winter rye crop management (managed as a cover crop or silage), ii) method of manure application (broadcasted or injected); and iii) timing of manure application (applied early in the fall or late, September or November respectively); that would reduce nutrient losses from a fall manure application and conserve manure-N for crop utilization in a no-till cropping system with winter rye planted in the fall followed by corn silage planted in the subsequent spring. We hypothesized that injecting manure as compared with broadcasting it; and applying manure late in the fall compared with early fall manure applications would reduce N losses and conserve more for crop utilization.

Previous reports, the 2014 and 2015 Northeast SARE DCS Project Progress Report, focused on the effect of fall manure application method and timing on winter rye and corn silage biomass. In addition to crop biomass, prior to corn planting and following winter rye termination or harvest, we measured soil nitrate to determine if main treatment effects affected residual soil-NO₃-N concentrations at different depths within the soil profile. Deep soil cores were obtained in each treatment plot to a depth of 90 cm using a Giddings hydraulic probe (Giddings, Ft. Collins, CO 80522). In treatment plots that received broadcasted manure, three cores were composited based on the depth to produce six samples per plot: 0-15cm, 15-30cm, 30-45cm, 45-60cm, 60-75cm, and 75-90cm. In treatment plots that received injected manure, a different method of sampling was used to avoid under or overestimation of concentrations soil-NO₃-N if taken randomly. When the location of the band was unknown, five soil cores were taken perpendicular to the direction of manure application across 76.5cm in 15.2cm increments to cover the distance between injection bands. Cores were separated by location across the 76.5cm and the six depths previously described. When manure bands were marked after a late manure application, sampling was reduced to three soil cores- one on: the manure band, 15.24cm from the band, and 30.48cm from the band. Soil cores were then separated by location and depth. Soil was dried in a greenhouse and ground to 1mm using a hammer mill. Soil samples from the 30-60cm and 60-90cm depths were combined and a total of four depths represented the soil cores taken from plots: 0-15cm, 15-30cm, 30-60cm, 60-90cm. Soil samples were sent to the Pennsylvania State University Agricultural Analytical Services Lab (University Park, PA), to be analyzed for nitrate. Soil-NO₃-N concentrations were statistically analyzed using the PROC Mixed procedure in SAS. Data was pooled across years. Each main factor: i) how the winter rye was managed; ii) how the manure was applied; and iii) when the manure was applied; year, and all the interactions with main factors were included in the model as fixed effects. Replicated blocks were nested in year and treated as a random effect. The ‘SLICE’ statement was used to determine least square means and to perform partitioned analyses of LSMEANS to determine the effect of management strategies. Differences were considered significant when p<0.05.

Results

Soil NO₃-N Differences by rye crop management

In 2014, soil NO₃-N after a cover crop tended to be higher than ryelage at the 0-15cm depth, but the difference was only significant when manure was injected (Figure 17). Soil NO₃-N was 71 and 36% higher after a cover crop than after ryelage when manure was injected in early and late fall respectively (Figure 17 b,d). No significant differences in soil NO₃-N were found due to rye crop management at deeper soil depths. Similarly in 2015, soil NO₃-N tended to be higher when rye was managed as a cover crop than when harvested for ryelage (Figure 17). Differences were significant at shallow depths when manure was applied late in the fall. After a late-broadcasted manure application, soil NO₃-N concentrations were 240 and 159% higher after a cover crop than after ryelage at the 0-15 and 15-30cm depth respectively (Figure 17g,h). After a late-injected manure application, soil concentrations were 74 and 155% higher after a cover crop than after ryelage. At the 30-60cm depth, soil NO₃-N concentrations were 89, 100, and 59% higher after a rye cover crop than after ryelage, when manure was injected early, broadcasted late, and injected late respectively (Figure 17 f, g, h).

Across both years, winter rye biomass and N-uptake in aboveground biomass was lower when managed as a cover crop than when harvested for ryelage (Table 3). Residual soil NO₃-N tended to be higher after a cover crop than after ryelage. The rye cover crop grew for a shorter period of time and more nitrogen was conserved in the soil. Ideally, higher concentrations of NO₃-N after a cover crop would remain in the soil for subsequent crop use; but there is also the  potential for N-leaching and other pathways of loss in the time period between cover crop termination and subsequent crop establishment.

Soil NO₃-N Differences by method of manure application

In 2014, soil NO3-N concentrations at the 0-15cm depth, following a rye cover crop, were 73 and 74% higher after manure was early- and late-injected than when early- and late-broadcasted respectively (Figure 18 a, b). Following a cover crop, soil NO₃-N concentrations were 91 and 73% higher after early-injected manure than early-broadcasted at the 30-60 and 60-90cm depths respectively; and 82, 54, and 84% higher after late-injected manure than after late-broadcasted respectively (Figure 18 a, b). Following ryelage, after an early manure application, soil NO₃-N was 96% higher after injected manure than broadcasted at the 60-90cm depth (Figure 18 c). After a late manure application, soil NO₃ concentrations were 61% higher after injected manure than broadcasted (Figure 18d). In 2015 following a cover crop, soil NO₃-N concentrations were 97% higher after early-injected manure than broadcasted at the 30-60cm depth; and 173, 174, 114% higher after late-injected manure than late-broadcasted at the 0-15, 15-30, 30-60cm depths respectively (Figure 18 e, f). Following ryelage, soil concentrations were 435, 168, and 175% higher after late-injected manure than late broadcasted at the 0-15, 15-30, 30-60, and 60-90cm depths respectively (Figure 18h).

Although differences in soil NO₃-N due to the method of manure application were not always consistently significant in 2014 or 2015, NO₃-N concentrations tended to be higher when manure was injected than when broadcasted. Immediate incorporation of manure using the shallow disc injectors reduced volatilization; increased ryelage biomass in 2014 and 2015 after and early manure application (Table 3); and differences in soil NO₃-N tended to persist after broadcasted and injected manure, despite the trend of higher N-uptake when manure was injected (Figure 18, Table 3). At shallow depths, higher concentrations of NO₃-N remaining in the soil could be available for the following crop, but also susceptible to other pathways of loss. Higher concentrations of soil NO₃-N at the deeper depths following injected manure, will most likely be unavailable to the following corn crop and has a higher potential to be lost by leaching.

Soil NO₃-N Differences by method of manure application

In 2014 and 2015, differences in soil NO₃-N due to the time of manure application was significant when manure was injected (Figure 19 b, d, f, h). Following a cover crop, soil NO₃-N at the 0-15cm depth was 42% higher after late-injected manure than early-injected manure in 2014 and 149% in 2015 (Figure 19 b, f). Further in the soil profile in 2015, soil NO₃-N concentrations were 194 and 30% higher after late-injected manure than early-injected at the 15-30 and 30-60cm depth respectively (Figure 19 f). Similarly following ryelage, soil NO₃-N at the 0-15 cm depth was 70 and 134% higher after late-injected manure than early-injected in 2014 and 2015 respectively (Figure 19 d, h). At the 30-60cm depth, soil NO₃-N concentrations were 43 and 56% higher after a late-injected manure than early-injected in 2014 and 2015 respectively (Figure 19 d, h).

Consistently across years, there were no differences in soil NO₃-N due to time of manure application when manure was broadcasted. Following a cover crop and ryelage, when manure was injected soil NO₃-N tended to be higher after a late fall manure application than an early fall application. The length of time that the manure is exposed to the elements and soil microbes is longer when manure is applied earlier in the fall rather than later, leaving manure-N more vulnerable to losses through pathways such as volatilization, run-off, and leaching.

figures 17-19

Table 3

Conclusions

For each management strategy there were agronomic and environmental tradeoffs. Coupling a winter rye with fall manure applications can reduce the erosion, run-off, and leaching. Managing rye as a cover crop trends to leave higher concentrations of soil NO₃-N in the soil for the following crop, but with a longer time period between cover crop termination and corn planting, soil NO₃-N is vulnerable to losses. Soil NO₃-N following a ryelage crop has the potential to increase total forage production, but will require additional fertilization to optimize crop yields. Injecting manure reduces volatilization and conserves more nitrogen in the soil. With trends of higher soil NO₃-N concentrations in the soil after injected manure than broadcasted manure, more NO₃-N could be conserved for subsequent crop utilization, but could be lost by leaching. Similarly, delaying fall manure applications can also reduce volatilization losses, and the observed trends of higher soil NO₃-N after late injected manure than early injected can be available to the following crop, but can also be lost.

Pest Rotation: Yields

Crop yields did not differ between the reduced herbicide (RH) and standard herbicide (SH) treatments for all of the crop entries, except for the 3^rd year alfalfa-orchardgrass and alfalfa stands in 2016 (Table 4). The third year SH alfalfa yielded 35% more than RH alfalfa and orchardgrass. There appear to be two factors that could explain the lower yield of the RH treatment. The pure SH alfalfa produced higher yields than the alfalfa and orchardgrass RH mixture in late June and mid-August harvests (data not shown), possibly because alfalfa is more productive under dry, warm summer conditions then orchardgrass. And because this forage entry was terminated in August to plant canola, the autumn yield that the orchardgrass might have produced in the RH treatment in fall was not realized. In addition, the alfalfa in the RH treatment was the potato leafhopper (PLH) resistant variety, and the SH alfalfa was not PLH resistant. And as discussed earlier in the manure rotation yield results, the leaf hopper resistant alfalfa variety planted with orchardgrass yielded 15% less then the non-resistant alfalfa planted with orchardgrass this year in the second year stands. In the manure rotation, both treatments had alfalfa and orchardgrass and both were also harvested in autumn, suggesting there was a yield-drag associated with the PLH trait this year in both rotations in these older stands.

Table 4

Across Rotations Yields:

We also compared corn and soybean yields among the two diverse rotations (PEST and MANURE rotations) where pests are managed with IPM to the low-diversity rotation (C-S rotation) where pre-emptive pest control practices are used (Project Schematic). Similar to 2015, soybean yield in 2016 did not differ between the PEST and C-S rotations and did not differ between RH vs. SH and IM vs. BM treatments nested in each rotation respectively (Table 5). Corn grain yield in 2016 was also similar in the MANURE and C-S Rotation (p = 0.25; Table 5), and there were no significant differences between the two injection and broadcast manure treatments in either rotation.

Table 5

Canola populations and slug activity density and damage assessments (2015-2016)

In the pest rotation, winter canola is planted after alfalfa and is either terminated with plowing to eliminate an herbicide (RH) or with an herbicide (SH treatment). The 2015, canola populations counted 40 days after planting did not differ between the tilled RH and no-till SH treatments (Figure 20). In 2016 however, tilled RH treatment had 34% more canola plants compared to the SH (Figure 20). Average slug activity density between 10/6/2016 and 11/8/2016 was 150% higher in the no-till SH plots compared to the tilled RH treatment in 2016 (Figure 21) . In spite of higher slug activity densities in the no-till, SH treatment, slug damage to the canola plants did not differ significantly between the treatments in both years (Figure 22). The lack of a significant plant damage difference between the treatments in both years, may be because slugs consumed canola seedlings prior to the plant populations and damage assessments were conducted 40 days after planting.

In previous years, we had planted canola in mid-September when we found slug activity tended to increase. In those years slug activity density was typically higher in the SH treatment, and canola populations were reduced compared to the RH treatment. Therefore, to improve the establishment on no-till SH canola, in 2012 we began terminating the alfalfa earlier in order to plant the canola by Aug. 25-27. In 2016, however the dry weather limited alfalfa regrowth after the third harvest, delaying our ability to terminate the alfalfa early with an herbicide.  In 2016 canola was delayed until September 8,  compared with August 28 , in 2015. Although the dry fall weather also limited the canola plant establishment in 2016, this delayed planting also likely coincided more the increased slug population activity  in mid-September, contributing to the lower SH canola plant populations.

figures 20-22

Integrated Pest Management, Scouting, Insect and Slug Control

Our efforts in implementing Integrated Pest Management in the two diverse dairy crop rotations in 2016 continued to focus on evaluating foster strong predator populations, which in turn can reduce pest populations, including slugs and caterpillars, and the damage these pests cause. In particular, we scouted slug populations and damage by slugs, presence of European corn borer in corn plots, and potato leafhopper population assessments in first and second year alfalfa plots.  By contrast in the corn-soybean control rotation, there are no cover crops that might provide predatory habitat and both the seed insecticide treatment and the insecticide sprays at corn planting can reduced predator populations.

Slug Damage In Corn

Slug damage was assessed by randomly selecting either two or four 10ft lengths of a split-split plot depending on treatment. Each corn plant was examined within the 10ft length. Plant damage at the V2 growth stage was predominately given a 0 or 1 rating (0-10% damaged). Within the Pest Corn Silage (CS Pest) rotation there was a significant decrease in the number of plants damaged compared to the manure rotation. Within the pest rotation an average 3.1 plants were damaged compared the range of 5.3 to 7.7 in the other rotations.  This decrease in the CS Pest rotation continued into the V5 stage (Figure 23) with an average of 7.3 plants damaged. Part of this decrease in plant damage in the CS Pest rotation may be explained by the significant decrease in the number of plants per 10ft found during the V5 stage (Figure 25).  This difference could be indicative of poor corn establishment in CS Pest rotation compared to the other rotations. There was also a significant decrease in plants damaged in the Manure Corn Silage (CS Manure) rotation at the V5 stage compared to the to the Control rotation.  However, unlike the CS Pest, following the trend that we have seen in previous years of more diverse corn rotations having reduced slug damage compared to the Control rotation, the corn grain plants in the Manure rotation did not have less damage then the pest rotation (Figure 24). Plant damage rating at V5 was predominately ranked as 1-2 (10-20 % damaged), and tended to occur on the oldest leaves on the plant (data not shown).

The soil disturbance by the high residue cultivator and tillage in previous years in the RH treatment may explain this difference. The manure and control rotations had not had any tillage or soil disturbance in the past six year. In the pest rotation, the RH main-management (half of the corn plot) was tilled 2,5 years ago to terminate alfalfa instead of using an herbicide in the no-till SH treatment. And the year prior to corn planting, one quarter of the RH plots were cultivated twice with a high-residue cultivator to control weeds in soybean (HR sub-management).  This soil disturbance in prior years to a portion of the Pest rotation corn plots may explain the lower corn plant slug damage, as this fall and in some previous years, slug activity density was lower and canola populations were higher in the tilled RH treatment plots compared to the no-till herbicide SH treatment plots. We also observed some reduction in slug activity density in the RH treatments in corn in previous years. 

European Corn Borer (ECB) Damage

At the end of August, we assessed European corn borer populations in the corn plots by recording feeding damage and lodged corn plants. Overall, there was an insignificant amount of European corn borer damage in all corn rotations and the treatments did not differ significantly (Figure 26). All the rotations had an average number of tunnels below the economic threshold of 1 ECB (tunnel) per corn plant (Figure 26). Though plants within the control plots were the least damaged of all rotations, the amount of damage was very minor amoung the treatments. Lodged plants were not found in the Control rotation and the corn silage after the interseeded cover crops (CS Int) treatment in the Manure rotation. The number of lodged plants was significantly higher within the non-interseeded corn silage treatment planted after alfalfa and orchardgrass (CS AOg2) in the Manure rotation, and the corn silage in the Pest rotation (CS Pest), compared to the other three treatments. Transitioning to a BT corn variety for the corn grain in the Manure (CG Manure) rotation as mentioned last year maybe premature as the difference was not significant between the corn grain in the manure and control rotations, and both were below the economic threshold.

Sentinel Prey Assessment

We assessed the predation within each corn rotation by the use of 16 sentinel waxworms per corn plot. We recorded how many waxworms survived over two twelve-hour periods (within 24hrs) to assess the predation during the day (until 8:30pm) and night (until 8:30am the next morning). There were no significant differences in the number of waxworms that survived in July, or August between all corn rotations in either the day or night assessment (Figure 27).  In June, there was a siginificant decrease in waxworm survival at night between the Manure and Pest rotation where approximately 18% fewer waxworms survived in the Manure than in the Pest rotation. Waxworm survivial at night in all rotations during August is the lowest survival rate in the past three years. This rate may indicate a higher predator pressure than in previous years, perhaps due to drought conditions experienced in late July and August.  Though there was no significant predation difference this year between the control and diverse rotations in June.

Potato Leafhopper Populations

The increase in potato leafhopper populations in 2016 was similar to what we have seen in previous years with the height of their presence occurring in late June and early July (Figure 28). We understand that the leafhopper resistance trait is not fully expressed in the establishment year, but leafhopper resistant alfalfa varieties appear to be effective in significantly reducing population numbers, which is best seen in late July as the leafhopper population increased. The drought that occurred around the same time as the leafhopper population peak made it diffcult to harvest rather than spray insecticides to reduce their numbers, yet visually we observed that the majority of the leafhopper resistant varieties appeared to avoid much damage and being sprayed until harvest. These varieties, both in the short and long term, have reduced the frequency of insecticide use, allowing us to harvest the alfalfa at the most opportune time.

figures 23-28