Final Report for GNE11-022
Forage radishes have been used to break up soil compaction in row crops. In this project I am investigated the physical and chemical changes that occur as a result of forage radish roots growing in non-till pasture. Typically forage radishes (Raphanus sativus) are sown between June 15 and July 15 so that the above ground growth can be grazed by cattle. In the winter radishes are killed by frost and decompose quickly in the spring. In row-crop systems, radish residues will be mixed with compacted soil during tillage eliminating holes. In no-till pasture radish holes would have to be filled in by redistribution of surface materials. I am interested in seeing what effects radish roots have on soil organic matter, soil density at the root level and how infiltration and runoff rates at the field level are affected by the ephemeral presence of radishes in the pasture. A sandy loam pasture soil was sown with radish in early July, 2012 at a seeding density of 8000 seeds per acre and allowed to grow for 12 weeks. In the late summer of 2012 soil core samples were taken to a depth of 20 cm; we also sampled earthworms near the radishes and in a control paddock without radishes. Soil organic matter was greater at the surface than at the lower depth. It was greater near the root than away from the root. At the soil surface density was lower near the root, an unexpected finding, and greater further away. In the spring of 2013 core samples were taken again as well as sampled earthworms, infiltratration rates and forage samples. All samples were analyzed and no significant differences were found.
The purpose of this project was to evaluate the potential for forage radishes (Raphanus sativus) to improve pasture forage production and soil quality. Cattle exert a static pressure on the soil upwards to 300 kPa when walking (Herbin et al. 2011) – more than three times that of an unloaded truck (Greenwood & McKenzie 2001). Cattle treading can result in soil compaction which restricts root growth, inhibits air and water movement, and thus decreases forage production (Drewry, et al. 2008; 2004). The potential for cattle to cause soil compaction increases with soil moisture. When soils are saturated, as is often the case during spring and fall, graziers are left with two options: they can either send their cattle to pasture risking plugging and considerable soil damage, or they can confine their cattle to a feedlot and supply the animals with costly grains. Graziers need a simple tool which will both mitigate existing soil compaction and improve water infiltration thereby enabling them to fully utilize their fields during all seasons and maximize profits.
Forage radish root holes may help to dry out persistently wet soils. The biodrilling radish roots penetrate compact soil layers upwards to 14 inches. The decomposition of the root in the spring creates an open conduit for water and air to penetrate deep into the soil profile. The channel may also increase the rate water permeates and evaporates from the soil. A similar technique, known as vertical mulching, has been used for over 50 years to improve water infiltration, improve soil physical properties, and reduce erosion in golf courses and agricultural fields (Byrne et al. 1965; Saxton et al. 1980). It consists of mechanically creating deep channels into the soil and filling them with crop resides. Rather than creating the holes with an auger or drill, I propose an alternative, lower energy method that uses the tap-rooted forage radish to create organic matter filled holes. To date, no study has formally considered the use of radishes to improve water permeability. However Weil & Kremen's (2007) observation that only a “very high” applied rainfall intensive resulted in run-off from agricultural fields cover-cropped forage radish, hints at the promise of this innovative concept. Eliminating excess soil moisture from pastures will reduce the potential for damaging soil compaction to occur, improve forage growth, and decrease emissions of nitrous oxide, a greenhouse gas released from saturated pasture soils.
The incorporation of radishes in pastures may have additional benefits besides improved soil water management. Brassica crops, including radishes a commonly sown in late summer to provide high quality feed in the autumn when pasture quality is limited. The radish tops provide a large quantity of highly digestible, carbohydrate- and protein-rich forage (Ayres & Clements 2002). They are widely used and university extension programs actively recommend planting forage radishes in agricultural fields to improve soil physical properties and reduce erosion. The rapid decomposition of the root residues in the spring significantly increases the concentration of nitrogen into the topsoil (Dean & Weil 2004), crop root density at depth (Chen & Weil 2009) and soybean and maize yields (Williams & Weil 2001). The substantial input of root dry mater was also observed to increase microbially active organic matter and total organic matter (Weil & White). I propose investigating whether these benefits to soil quality and crop production are transferable to pastures.
In contrast to other pasture remediation tools such as subsoiling, radishes are low input and low cost. Planting radishes can be broadcast seeded and does not require large machinery making it one of the few pasture remediation tools available to areas too steep or rocky for tractors. It is a hardy plant that will establish rapidly under a wide variety of condition. As tool to reduce compaction, forage radishes are a less expensive alternative to subsoiling or deep tillage; seeds cost about $15 an acre -- $18 to $30 less per acre than contract subsurface tillage (Johnson et al. 1993).
Forage radishes may offer farmers a new tool to improve farm productivity and sustainability. While forage radishes are already incorporated in pastures as supplemental forage, they have never been evaluated as a tool to remediate wet, compact pastures. At the 2010 Vermont Grazers Conference, attendees of a compaction workshop were primarily interested in research regarding forage radishes in pastures. Given the established environmental advantages of pasturing over confined feedlots, it is important to encourage research into low cost tools that enhance of long-term sustainability and profitability of the pasturing cattle. The data gathered through this research will support the need of the farming community for a reliable and profitable remediation option for wet, compact, low quality pasture soils.
Summer 2012: Soil core samples were taken at 0, 10 and 30 cm to a depth of 20 cm radiating from the forage radish (FR) root and soil cores were also taken from an untreated control plot (CP). Earthworms (EW) were sampled by the removal of soil from 30X30X30 cm cube of soils. Earthworms were collected by hand sorting and were identified to ecological group by morphological and pigment characters. Analysis of the cores was performed in the lab at UVM. The core samples revealed that at the soil surface density was lower adjacent to the root (0.78 g/cm3) than at 30 cm (0.92 g/cm3) from it, but there was no difference among distances for the 10 - 20 cm depth increment (1.3 g/cm3). Similarly, organic matter differed only at the surface between the 0 (11%) and 30 cm (9%) distance. There was no significant difference in dry root mass among distances from the root and soil depth. Earthworm density was greater near radish roots.
Summer 2013: Soil core samples were taken at 0, 10 and 30 cm to a depth of 20 cm radiating from the forage radish (FR) root and soil cores were also taken from an untreated control plot (CP). Earthworms (EW) were sampled by the removal of soil from 30X30X30 cm cube of soils. Earthworms were collected by hand sorting and were identified to ecological group by morphological and pigment characters. Analysis of the cores was performed in the lab at UVM. The core samples revealed that specific soil quality indicators such as SOM, dry root weight, bulk density and N-NO3 there was no significant difference amongst treatments at the .05 level of significance. Although there was no significant difference at the .05 level there seems to be a slight difference with volumetric water content at the 10-20 cm depth (p-value = .172; control = .496 & adjacent to radish = .858), active carbon at the 10-20 cm depth (p-value = .13; 10 cm from radish = 616 mg/kg; control = 872 mg/kg; adjacent to radish = 742 mg/kg; and 30 cm from radish = 801 mg/kg), and N-NH4 at the 10- 20 cm depth (p-value = .13; control = .468; adjacent to radish =.557; 10 cm from radish = .681; 30 cm from radish = .529).
*Most difference occurred at the 10-20 cm depth, not the surface (0-10cm)
- Assess the impact of forage radish on forage production and quality.
The measurement of forage production and quality was not assessed. The project collaborated between multiple students and the timely processing of the cut forage samples was not performed and was unable to produce accurate results under laboratory testing.
- Monitor impacts of forage radish growth and decomposition on soil infiltration rates.
During the spring and summer of 2013 multiple tests were performed with a Cornell Sprinkler Infiltrometer on all treatments. Under all samples tested, there was no measurable difference between treatments. The infiltrometer on all tests was unable create runoff due to the high infiltration rate of water into the soil profile and therefore no calculations could be made.
- Use experimental results to develop and distribute relevant and appropriate fact sheets for use by farmers and agricultural professionals describing how to utilize forage radishes in pastures and the possible advantages of doing so.
A fact sheet has been developed with conclusions and discussion points based off of findings from soil quality indicators.
There were two treatments: radish present or no radish present (control). Two paddocks were used for this study a control paddock and a forage radish plot. The control paddock was not be seeded while the forage radish plot was broadcast seeded at 8,000 seeds/ac in late July 2012.
Plot Establishment: We have selected paddocks at Choinere Famil Farm in High Gate Center, VT. The predominant soil texture in each plot was verified using the hydrometer method. Originally, over the course of the experiment livestock was to be excluded from the research site; however, grazing requirements by the farmer led the experimental plots to be grazed. This grazing prevented us from delineating plots with small flags and therefore allowed for a randomized sampling approach. Two paddocks were selected and each given one of two treatments, presence or absence of forage radish. Each paddock was given a 2 m buffer.
Establishment of Forage Radish: The forage radish treatment paddock was broadcast seeded in late summer 2012 and compared with a control paddock with no radish seeded.
Objective One: Soil Quality Indicators?Soil moisture and organic matter content were measured over the course of the experiment, on equivalent experimental units in each treatment paddock. Sampling occured during time periods associated with the following events: (1) late autumn when forage radish achieve maximum growth, (2) early spring when pasture is snow free and the root begins to rapidly decompose, (3) mid- summer when forage growth rate is maximized and (4) late summer when plants are more likely to be moisture stressed. During each time period, 3 core samples were taken from the control plot and 9 core samples were taken from the forage radish plot ( 3 cores radiating from 3 radish roots).
The forage radish experimental plot was sampled along three 10-20 cm long transects radiating from the center of the radish root. Along each transect, a soil hammer corer was used to remove 3 20 cm long undisturbed soil cores at 0 cm, 10 cm, and 30 cm away from the center root. The remaining 10 cm deep layer was excavated using a shovel and hand sorted for earthworms. I then repeated the process described above two more times, removing cores and enumerating earthworm in the 20-30 cm depth. Samples were bagged, transported to the lab in a cooler and stored at 4°C for no longer than one week until analysis. This sampling procedure is designed to detect small changes in soil chemical properties through extensive replication. It also enabled us to estimate the distance being affected by the root decay by establishing spatial gradients.
At the lab, samples were immediately weighed. All samples were passed through a 5 mm sieve separate the roots from the soil. Roots were dried for 24 hours at 70°C and reweighed to determine below ground biomass. A 5 gram subsample of fresh soil was weighed and oven-dried at 105 C for 24 h, and reweighed to determine gravimetric moisture. Bulk density and volumetric moisture content was calculated from gravimetric moisture data in sample initial fresh weight. The sample was then heated to 450°C in a muffle furnace for 8 hours and reweighed to determine percent organic matter. The remaining soil sample was air-dried for 24 hours and passed through a 2 mm sieve. A 2.5 gram and 4 gram subsample was removed for active carbon and available nitrogen determination, respectively. The concentration of active (labile) carbon was measured following the procedure developed by (Weil et al. 2003) which quantities the oxidation of organic matter by measuring the absorbance of a 0.02 M solution of potassium permanganate after being reacted soil. Since most root residues are part of the labile organic pool, I expect labile carbon concentrations to be more sensitive to root decomposition. In other pasture based experiments, active carbon was shown to be more responsive to management effects than organic matter and more closely related to biogeochemical soil process. Extractable nitrate, nitrite, and ammonium concentrations were measured using colorimetric analysis by a microplate reader following extraction with a 1M KCl solution following protocols developed by Doane and Horwath (2003). Since nitrogen, is often the limiting nutrient in pastures, soil available nitrogen is a strong indicator of a pasture’s capacity to sustain forage.
Objective Two: Forage production and quality? was measured three times, over the course of the experiment, on equivalent experimental units. (1) late autumn when forage radish achieves maximum growth, (2) early summer when forage growth rate is maximized and (3) late summer.
During each sampling period, 50cm square swards of forage was collected from the center of each experimental unit by clipping the forage with scissors to a height of 1 inch. Forage was bagged and immediately weighed to determine forage fresh weight. Samples were analyzed by Dairy One for typical forage quality indicators including dry matter, crude protein, crude fiber, crude fat, and ash. The remaining forage in the experimental fields was mowed, bagged and removed from the site to simulate grazing.
Objective Three: Infiltration Rate and Sorptivity?Soil sorptivity, saturated infiltration and time to run-off was measured once a month, during all snow-free months, on all experimental plots using a portable rainfall simulator (Cornell Sprinkle Infiltrometer). This established method provides an easy, low cost, rapid measurement of a variety of soil water movement parameters; the method wets soil more naturally thereby eliminating soil slacking and unnaturally high influence of macropore flow. We constructed a larger (12” diameter) sprinkler infiltrometer following directions provided by Cornell University.
A single 12" inner diameter infiltration ring was inserted in the center of each experimental plot surrounding the radish root when present. Care was taken to not disturb the soil. Using an overflow tube assembly installed in the ring, water from the ring was allowed to drain into a beaker installed greater than one meter from the plot installed below the soil surface. Simulated rainfall was applied to the soil at a wide range of predetermined rates. Measurements of infiltration rate were collected following standard procedures.
To determine initial soil moisture content, we used a hammer corer soil probe to collect three, 10 cm deep soil samples within each plot in an area greater than one-meter from the location where simulated rainfall is being measured. Fresh soil samples will be weighed and oven-dried at 105 C for 24 h, and reweighed to determine volumetric moisture content. This data was used to standardize sorptivity measurements during the duration of the experiment.
Objective Four: Economic and Environmental Analysis:?If the results of my experiment demonstrated improved pasture productivity and/or water infiltration in plots with forage radish, I would work closely with member of the Center for Sustainable Agriculture and Gund Institute for Ecological Economics to develop a cost-benefit analysis for seeding forage radish in pastures. The analysis compared the improvements in forage and soil quality against the cost and labor associated with planting radishes taking into count soil type, farm size, and herd size.
The results were used to generate a detailed fact sheet describing the use of forage radish in pasture and its advantages aimed toward the farming community and agricultural professionals.
An ungrazed pasture with a sandy loam soil in High Gate Center, VT was seeded with forage radish at a seeding density of 8000 seeds per acre in early July, 2012. The plot remained ungrazed during the initial growth period and soil core samples as well as earthworm samples were taken on October 17, 2012. I performed lab analysis of soil organic matter, bulk density, and dry root weight during October and November 2012. I concluded that in the fall 2012, 12 weeks after sowing, there were differences in the spatial distribution of soil properties as a function of distance from radish roots.Soil core samples were taken at 0, 10 and 30 cm to a depth of 20 cm radiating from the forage radish (FR) root and soil cores were also taken from an untreated control plot (CP). Earthworms (EW) were sampled by the removal of soil from 30X30X30 cm cube of soils. The core samples revealed that at the soil surface density was lower adjacent to the root (0.78 g/cm3) than at 30 cm (0.92 g/cm3) from it, but there was no difference among distances for the 10 - 20 cm depth increment (1.3 g/cm3). Similarly, organic matter differed only at the surface between the 0 (11%) and 30 cm (9%) distance. There was no significant difference in dry root mass among distances from the root and soil depth. Earthworm density was greater near radish roots.
In the spring and summer of 2013, more soil core samples were taken as before on the FR and the control plots to be analyzed again for soil quality indicators. As the FR root decomposed, continuous samples were taken over time to assess the impact of the FR root on soil quality indicators and infiltration rates. The core samples revealed that there was no significant differences or trends in any measurements at the 0-10 cm depth; however, at the 10-20cm depth there appeared to minor differences spatially even though they are not significant. Organic matter was highest closer to the radish root compared to the control plot: 0 cm (7.14%), 10 cm (7.01%), 30 cm (6.89%), and control (6.16%). Bulk density was lowest adjacent to the FR root (.003g/cm^3) compared to the control (.006 g/cm^3). FR treated plots had greater volumetric water content compared to the control: 0 cm (86%), 10 cm (82%), 30 cm (77%), and control (49%). Soil nitrate levels were higher adjacent to the FR root (2.43 g/kg N-NO3) and at 10 cm (2.7 g/kg N-NO3) compared to the control (1.04 g/kg N-NO3). Although there was variation amongst spatial differences, there was no significant differences to draw conclusions from.
Continuing beyond spring 2013, data analysis was performed and compared to the fall 2012 results along with the control throughout the 2013 season. Fact sheets were be prepared in the fall of 2013. Comparing the soil quality indicators from 2012 to 2013, it is possible that the increased organic matter at the surface in the fall of 2012 has translocated to greater depths in the following spring of 2013 and therefore increasing volumetric water content closer to the FR root as well as lowering the bulk density. This however is inconclusive due to lack of significant evidence.
To date I have analyzed soil cores and the distribution of soil properties around FR roots. These data and information to be generated is included in a factsheet to be distributed through the NE Pasture Network (see ‘Forage Radish Fact Sheet - Research Update’ attached).
The results of this experiment may change with increased sampling or under different management practices. Since no significant differences were found with the varying soil quality indicators, it may be a sign that the current practices of the pasture are working positively. Perhaps with a poorly managed soil differing results may occur. There did seem to be a significant difference in earthworm population suggesting an increase in biological activity independent of other soil quality indicators measured.
Education & Outreach Activities and Participation Summary
Areas needing additional study
- Increased sampling (where there was difference, but not significant, could increased sampling provide more power to the results?)
- Difference in seeding density? Soil types(study the use of forage radish on known compacted soil and soils of potential concern(clay soils)? Management practices? Past history?
- Analyze at greater depths. Where minor differences were present, it was only at the 10-20 cm depth and not at the surface. Perhaps, sub 20 cm there could be affects to the soil profile.