Hydroseeded mulch as an alternative to plastic mulch films

Final Report for OS07-034

Project Type: On-Farm Research
Funds awarded in 2007: $14,000.00
Projected End Date: 12/31/2008
Region: Southern
State: Georgia
Principal Investigator:
Dr. Gary L. Hawkins
University of Georgia
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Project Information

Abstract:

The project here is looking at the use of materials that can be used in place of plastic mulch for growing watermelons (and any other vegetables). The farmer involved with this project grows a rye and clover cover crop during the winter months, beds plastic beds for watermelons in Feb/March and the plants a second crop over the watermelon beds during the summer months.

The purpose of this project was to determine if alternative mulch, which is bio-degradable can be used to replace the HDPE plastic and would naturally degrade over time.

A second and main aspect of the project was also to find an alternative mulch that can retard weed growth until the watermelons can cover the soil surface.

Results indicate that newspaper and craft paper both provide good weed suppression while also allowing water to get to the root system.

Introduction

Plastic mulch is a generally used type of mulch in large scale production of fruits and vegetables in Georgia. The mulch is used specifically for multiple uses. One of these uses is to warm the soil when air temperatures is below that needed to germinate seed or provide a warm bed for growing transplants. Another reason for using plastic mulch is to retard weeds in the growing beds.
Some farmers interested in conserving soil and water resources employees the use of conservation tillage. Conservation tillage is a system of using cover crops along with reduced tillage to protect soil and water resources. Even when conservation tillage is used, some farmers will “lay” plastic mulch to provide a warmer soil as well as a barrier for weeds. In these systems, the plastic mulch is not usually pulled up before the next crop or if it is pulled then there is some remaining in the field that will not degrade and can cause problems with subsequent crops. One type of plastic mulch is photodegradable. Photodegradable plastic is designed to degrade when the plastic is exposed to sunlight. However, some of the plastic is “tucked” under the edges of the fruit and vegetable beds and is not exposed to sunlight. Some of the plastic, when the next crop is planted, is pushed underground and therefore is not exposed to the sunlight and cannot degrade. When this plastic does not degrade it can cause problems with future crops but it also pollutes the environment. Therefore, the major objective of this project was to explore potentially new mulches that will warm the soil, provide a weed retardant and decompose after the growing season.

Project Objectives:

1. Develop a system of recycling waste organic materials (i.e. cotton gin trash or compost) to form a thin strip useful for planting transplanted vegetables and fruits,
2. Use the developed hydro-mulching system on operating farm and control research plots to determine if the mulch is a viable alternative mulch especially in conservation tillage systems, and
3. Perform a cost analysis of this system verses traditional mulching practices.

Cooperators

Click linked name(s) to expand
  • Bob Rawlings

Research

Materials and methods:

The methods of setting up the project are explained in Section “Impacts of Results/Outcomes” below.

Research results and discussion:

The Results of this project are provided in detail in the Section entitled “Impacts of Results/Outcomes” below.

Participation Summary

Educational & Outreach Activities

Participation Summary:

Education/outreach description:

Information about the project has been distributed in multiple different means. This dissemination of information has been mainly to farmer groups to date. The information on the plastic layer has been presented at farmer meetings, the annual conservation tillage production systems conference, through farm visits and by word of mouth of the project collaborators.

Future plans for the dissemination of information will occur through professional organizations such as the Georgia County Extension Agents, other professional organizations and maybe even Extension Journals. The dissemination of this information will make other farmers more aware of the potential to use alternative mulches to retard weeds, be biodegradable and use a material that will not need to be removed from the field and disposed of in a solid waste landfill.

Project Outcomes

Project outcomes:

The results of this project have proven to be very successful. Success comes from many different aspects of the project which are described in detail below.

Retrofitting a standard plastic layer
A standard plastic layer was purchased and modified to be used in conditions where the field was planted in a heavy cover crop and then strip tilled to provide a bed for the planting of watermelons. The operation of planting watermelons begins annually in October. Mr. Bob Rawlings, the cooperating farmer, practices conservation production agriculture. In using conservation agriculture, Mr. Rawlings plants a cover crop in the timeframe of October/November of every year. This cover crop generally consists of either annual rye or clover. The cover crops are used to protect the soil in the winter months, provide nutrient cycling for the subsequent crops, provides a wind break during the early stages of the watermelon growing season and provides a decomposable biomass to aid in the accumulation of soil organic matter. The building of the soil organic matter is one of the vital parts of the conservation production system in that it provides means for increased infiltration, better soil quality and better soil biology.
Just prior to planting season for the transplanted watermelons, Mr. Rawlings will prepare the watermelon beds by first spraying the beds with a herbicide to kill a strip. Once dead, the beds are tilled to incorporate the residue and make the soil a little more amendable to laying plastic mulch for transplants. The tilled bed area is approximately 24 inch with the bed spacing being 12 feet (see Figure 1). After the beds have been tilled, Mr. Rawlings uses the modified plastic layer to install plastic mulch to accept transplants. The plastic layer has been modified to lay a narrow row, had brushes added to remove any soil and residue build up on the plastic that has occurred due to roughness of the tilled strip (see Figure 2).

Once the beds have been prepared, the plastic layer is pulled like a normal plastic layer to stretch the plastic to form a bed to receive transplants. The modified layer however has been designed to hold weights to aid in the downward pressure applied to the “tuck” wheels. This added pressure is needed in some locations where the cover crop roots and residue maybe in the slot for pressing in and covering the plastic edges, or “tuck” area of the plastic mulch.
The modified plastic layer has been used by Mr. Rawlings for three years and he says that the layer works great. Some of the bad parts about the layer are sometimes the soil conditions makes the layer look like it does not work. This not working is a result of the added root mass associated with the turned rye or the soil conditions may be a little wetter than normal. That was the case in the 2010 planting season. Mr. Rawlings was not able to get into the field to till the strip due to rain and wet conditions, therefore the rye did not breakdown as quickly as possible and he had to plant watermelons prior to the rye becoming brittle. This having to get into the field a little early forced him to modify the layer on the go in some places. Two of the modifications he performed was adding extra weight and moving the “tuck” wheels in or out a little. Overall Mr. Rawlings is very happy with the product and makes it available to others upon request to use for installing plastic mulch in fields that have cover crops planted in a conservation production system.

Installation of test plots for alternative mulches:

A second part of this project was to install various mulches to replace HDPE plastic mulch in Conservation Production System. Mr. Rawlings uses HDPE plastic mulch like most other fruit and vegetable growers for multiple reasons. Two of the main reasons for using the plastic mulch are increased soil temperature and weed suppression. Mr. Rawlings tries to purchase the photodegradable plastic for the purposes of the plastic degrading over time as it is exposed to the sunlight. However, as Mr. Rawlings notes, “The plastic that is not exposed to the sunlight does not decompose”. The non-decomposition of the unexposed plastic causes a problem in Mr. Rawlings field in that after the watermelon season is over, he comes right back in and plants another crop for a fall harvest. In the planting operation of this second crop he can press some of the plastic deeper into the soil. Therefore, this plastic is not exposed and does not decompose. This plastic then has the potential to adversely affect the next crop or crops planted in future years. The non-decomposed plastic has the potential of causing many different problems, some of which are: 1) the formation of a perched pool of water that could cause the plant roots to become waterlogged and die, 2) cause a hard layer that the roots cannot penetrate and thereby cannot grow and get the needed nutrients, and 3) can form a small pool that holds nutrients and does not allow the nitrogen to spread for the uptake by other plants. A simple diagram is shown in Figure 3.

With these potential and real problems, Mr. Rawlings has been interested in finding another solution to warming the soil and retarding weeds for his watermelon crop. With this grant we investigated five (5) different mulches that could be used on Mr. Rawlings farm or anyone’s farm. The five things tried were newspaper (4 layers), contractors paper or brown craft paper, compost, compost mixed with glycerin (the by-product of the bio-diesel process) and a new plastic that is biodegradable in a short time period (120 days in this case). Along with the different treatments we installed one test that was just bare ground but had been prepared as a normal watermelon bed.
The process we followed to install the different test plots was that Mr. Rawlings went through his normal bed preparation process as described above. Once he had completed bedding, we went in behind him and removed twenty-nine (29) feet of a row and placed in the treatment of interest. One exception was where we placed the compost, in the compost and compost with glycerin, we only used a nine (9) foot row length due to quantity of compost and glycerin. We randomly replicated this three times on three adjacent rows in an area of the field that had the same slope and soil type. The layout of the test plots can be seen in Figure 4 and a picture of the actually installed site is shown in Figure 5.

Once installed, watermelons were planted in each treatment and soil moisture sensors were installed as well as a temperature probe in one of the treatments as indicated by the star in Figure 4. The soil moisture sensors were installed vertically to monitor the top six (6) inches of the soil profile and the temperature probe was placed on top of the soil and directly under the plastic. The sensors used were manufactured by Decagon Devices. The use of these sensors does in no way signify an endorsement byteh University of Georgia or the collaborators.
To monitor the ability of the different mulches to retard or suppress weed growth, weed counts were taken weekly from installation. Weeds were counted in the mulched area only and were only pulled if they were those types that would cause a problem in the future. These would include pigweed, volunteer watermelons or other vines such as morning glories. All weeds were counted and if pulled, the numbers were noted and added to each weeks count as if they were still in the plots. The data was averaged across the like treatments and plotted. The resulting plot can be seen in Figure 6.

As can be seen in this plot, the control treatments did not retard any of the weeds. The main weeds noted in all plots were nutsedge, some pig weed, a few morningglories and volunteer watermelons. The weed count numbers were taken for the plot size and multiplied to normalize the data on a per acre base. As can also be seen, all mulch systems retarded or suppressed weeds. The main place where the weeds were not suppressed was in the opening of the mulch where the watermelons were planted and a few spots for nutsedge.
Another part of the project was to monitor the temperature under each mulch. This data is plotted in Figures 7, 8 and 9. The data indicates that the mulch that consistently had the highest and lowest temperature was the compost, however, it was one of the two treatments that had the most weeds growing. To show this a little better, the minimum and maximum temperatures were plotted and can be seen in Figure 7, 8, and 9. It is interesting that the compost has the largest variation in the high and low temperatures. As can be seen in the plot, the lowest minimum temperature is that of the compost and the highest minimum temperatures is the newspaper. It should also be noted that the treatment with the minimum temperature as well as the maximum temperature changes as the day progresses.
Associated with the installation of mulches, the project collaborators wanted to measure and monitor soil moisture and precipitation on the plots. As can be seen in Figure 10, the soil moisture

under the mulches responds to precipitation. Precipitation as defined here can either be natural rain or irrigation
via a center pivot. It can be seen in the plot that there is a difference in the amount of moisture held under each mulch with HDPE generally holding more moisture and the lower end of the moisture varies from mulch to mulch. Overall, the moisture is within the range (above 0.15 which is 15% moisture and below the 0.400 which is 40%, where 42% is saturated on these sensors) to provide ample water to the plants. Therefore, all of the mulches are holding water in the soil profile as expected.
Dissemination of Information:
Information about the project has been distributed in multiple different means. This dissemination of information has been mainly to farmer groups to date. The information on the plastic layer has been presented at farmer meetings, the annual conservation tillage production systems conference, through farm visits and by word of mouth of the project collaborators.

Figure 7. The temperatures of all mulches plotted on the same graph. Data was collected every 15 minutes.

Figure 8. The minimum temperatures on a 15 minute base.

Figure 9. The maximum temperatures on a 15 minute base.

Figure 10. Precipitation and associated soil moisture under each mulch as measured in the top vertical six inches of soil.

Future plans for the dissemination of information will occur through professional organizations such as the Georgia County Extension Agents, other professional organizations and maybe even Extension Journals. The dissemination of this information will make other farmers more aware of the potential to use alternative mulches to retard weeds, be biodegradable and use a material that will not need to be removed from the field and disposed of in a solid waste landfill.

Economic Analysis

The materials used in this project were newspaper, craft paper or contractor’s paper from the local hardware store, biodegradable plastic and regular HDPE plastic. Comparing the cost of each material, newspaper was the cheapest in that we only paid $5 for all the paper we could get from the local newspaper distributor. The $5 was only a donation not a direct purchase. The craft paper was the next cheapest material in that we purchased the roll of 200 feet for $10.00. The price of HDPE and then the biodegradable plastic was in line. The price of the HDPE and biodegradable plastic will depend on distributor.

One cost not figured in the cost estimates above is the labor required to install the materials. As would be expected the newspaper will have to be installed by hand. The craft paper maybe applied with a normal plastic layer, however we installed by hand after HDPE had been laid. The two plastics can be laid with a normal plastic layer.

Farmer Adoption

The adoption of this project by farmers will be based on the acreage of area used. For large acreagage, the use of these materials is more than likely feasible now, but could be if some minor changes are made. These changes could be blowing on the newspaper mulch or having rolls of craft paper that is slightly larger than is produced now. However, the use of either material (newspaper or craft paper) on small farms could be used and implemented very easily.

Recommendations:

Areas needing additional study

Although we used various mulches, the installation of these mulches was done by hand. The cost of the mulches maybe higher on a per acre base, but if used in a small plot this may not be of concern as opposed to a large area. Also, if the farmer is planting a large field, fifty plus (50+) acres, then some of these mulches are currently prohibitive (for example, newspaper and compost). However, if the farmer is interested in using some of the alternative mulches tested here, a means of applying the mulch maybe determined. For example, if craft paper is of interest, it currently comes on a roll and maybe possible to be laid with a plastic layer. Compost maybe applied in a thin strip with a mulch spreader used to control erosion. Newspaper could be rolled if rolls of the paper were available. Bio-plastic is available now, but the cost is higher than normal HDPE. If however farmers start using the plastic then the price may come down to a point that is comparable to normal HDPE plastic.
Overall, if farmers are interested, means can be found to apply the various mulches tested in this plot. That is the way that Mr. Rawlings started developing a modified plastic layer. He wanted to use plastic mulch in a conservation production systems operation, he now is interested in bio-degradable mulches that does a comparable job as HDPE but degrades over time. With farmers like Mr. Rawlings, I foresee such a system as the alternative mulches tested here being used in place of HDPE plastic.

Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.