The results of this study showed that the HT did indeed increase yields, height, and biomass. The greenhouse effect elicited by the plastic covering of the HT extended the season roughly two weeks both in the spring and fall. The results of this study also showed a general trend of larger amounts of available nutrients in the HT soil compared to OF soil. Likely as a result of greater rates of nutrient availability and a lack of leaching, soluble salt levels were greater in the HT compared to the OF, although not greater than the raspberry salinity threshold of 1.0 dS/m. It was difficult to determine how much of the nutrient difference was from greater mineralization or decreased leaching in the HT soil compared to OF soil, and how much of the nutrient difference was from the initial nutrient content. The leaf tissue results were mixed, but there was either no difference or only a small difference between the production systems in leaf tissue nutrient concentrations. Those results suggest that canes in the HT were taking up more nutrients, but using it to fuel a larger amount of growth than the OF canes.
High tunnels are defined as temporary, unheated, plastic-covered structures that provide an intermediate level of climate protection and control. Crops are planted directly into the soil inside the tunnel which traps solar heat to elevate temperatures a few degrees to extend the season both in the spring and fall. In addition to extending the season, this production system also offers protection from wind and rain damage, protection from some insects and diseases as well as birds and varmints. This unique environment presents an opportunity to develop a raspberry production system that requires reduced chemical inputs to manage pests and disease as well as increased control of nutrient management due to reduced leaching of nutrients through exclusion of precipitation. As this production system is different from field production, best management practices that have been established for field conditions may not apply in a high tunnel environment. In order to maximize the potential efficiencies and opportunities that high tunnel production presents, it is necessary to understand the opportunities and limitations that occur when utilizing this technology in different regions of the state. In particular, it is necessary to understand the nutrient management needs in the high tunnel system.
To assist in the development of this proposal, a survey was sent out through collaboration with the Wisconsin Berry Growers Association. The objective of the survey was to determine the level of interest in high tunnel production and to solicit feedback from producers about what they felt were top research priorities for high tunnel fruit production. Results of the survey indicated that 20% of producers surveyed currently had a high tunnel, but 63% of respondents indicated that they were planning on putting up a high tunnel in the near future. This interest has been influenced by the NRCS cost-share initiative through the EQIP program to assist in purchasing high tunnel structures in 2010 as many growers indicated they had applied to the EQIP program.
The survey also asked growers to identify the top three research priorities for high tunnels. The top responses were 1) Pest management 2) cultivar selection and 3) nutrient management. Other areas mentioned include pruning and trellising strategies, irrigation management, marketing and cost of production. In follow-up phone conversations, growers who are currently utilizing high tunnels indicated that information available from other regions is often not applicable due to the different climatic conditions. These responses clearly indicate that there is a need to develop a long-term research program to support an emerging high tunnel industry in Wisconsin.
1) Increase growers understanding of nutrient release rates in high tunnels to help growers make decisions about application rates and timing.
2) Increased awareness of the importance of tissue testing to determine crop nutrient needs.
3) Increased understanding of nutrient management plans and how they can improve nutrient management decisions.
4) Improved understanding of nutrient dynamics in high tunnels compared to field production.
5) Increased use of soil and tissue testing to aid in nutrient management.
6) Improved soil quality in high tunnels through the proper use of organic soil amendments.
This experiment began in 2011 and concluded in 2013. It took place at the West Madison Agricultural Research Station in Verona, Wisconsin (latitude 43º 3’ 39”N; longitude -89º 32’ 5”W) on a plot of land initially plowed in spring of 2011.
Design and Materials
Two adjacent (9.14 by 29.26 meters) plots of fall-bearing raspberry (Rubus idaeus, L.) plantings were established, one within a HT and the other in an OF. The experiment consisted of a split plot design, with a randomized complete block design nested within the whole plot factor. The whole plot factor was the production system, either the HT or the OF. Split plot factors were cultivar and fertilizer with four randomized blocks. Each block included two raspberry cultivars (‘Caroline’ and ‘Heritage’) and five fertilizers treatments (cow manure with leaf compost, mushroom compost, fish emulsion, urea, and a no fertilizer control), creating ten treatments per block and thus a total number of 40 plots per production system. Each plot was treated the same with USDA organic production practices, except the urea treatment plots. Five fertilizer treatments were applied including a control with no application. The fish emulsion, AgGrand Natural Fertilizer (AMSoil Inc., Superior, Wisconsin) and the soluble urea was applied weekly as a liquid. The compost and manure were incorporated into the soil prior to planting. It is important to note that urea is a synthetic fertilizer and cannot be used in an organic farming system. Here it was used as a synthetic control or check to the organic fertilizers.
For each 1.83 meter (6 ft) plot, five raspberry plants were planted into 0.3 meter (1 ft) deep holes every 0.46 meters (1.5 ft) along the middle of the row. Landscape-quality, black, 30 mil woven, UV-resistant polypropylene, needle-punched fabric (FarmTek, Dyersville, Iowa) was installed in the walkway to reduce dust and inhibit suckering from raspberries. Drip irrigation (Rain Bird, Azusa, California) was installed both in the HT and OF plots. . The timer outside had a rain gauge attached in order to avoid watering after a significant rain event. The timers were set to water 0.935 cm per day in both production systems. Watering was adjusted throughout the season in order to maintain field capacity of 40 to 45% volumetric water.
Select weather data was collected on the site. Air and soil temperatures were collected from both inside and outside the HT from March through December.
To assess nutrient availability, soil cores were taken from each plot throughout the growing season. The soil was analyzed by the University of Wisconsin (UW) Soil and Plant Analysis Lab (Verona, Wisconsin) for pH, NH4 (ppm), NO3 (ppm), available P (ppm), available K (ppm), pH, soluble salts (dS/m), and organic matter (%). Soil cores were taken at the depth of 0 to 25 cm. At the beginning of the season, soil samples were taken weekly for three weeks. Sampling then occurred every until August whereby sampling occurred monthly until October.
Plant nutrient status was tested by conducting plant tissue analyses during peak berry production, which occurred 6 October. Thirty leaves were taken from random canes at the 3rd to 5th node from the tip. Leaves were dried down in forced air drying ovens at 60° C for several days. Tissues were analyzed by UW Soil and Plant Analysis Lab for phosphorus (%), potassium (%), total nitrogen (%), calcium (%), magnesium (%), sulfur (%), zinc (ppm), boron (ppm), manganese (ppm), iron (ppm), copper (ppm), aluminum (ppm), and sodium (ppm).
Soil nitrogen. Throughout the season, the concentration of NH4 in the HT soil was significantly greater than the OF soil. The largest difference between both production systems occurred in the fall. Amongst all fertilizer treatments the HT soil was significantly greater in NH4 concentrations than OF soil, as well. The fertilizer treatment had an effect for soil NH4 concentration in the HT, but not the OF. In the HT, manure plots had the largest ammonium concentration. There were significant differences amongst the seasons in levels of soil NH4 across both production systems.
During the spring and fall, the HT soil had more NO3 than the OF soil, while in the summer there was no difference between the production systems. There was a seasonal difference in soil NO3 concentration in the HT with very large values in spring. Overall differences between the average production systems NH4 concentrations seemed to be due to the background amount of NH4 in the soil. The soil tests from 2011, before any treatments were applied or the HT was installed, showed that the HT soil had a total N level that was 141% greater than the OF soil. In 2012, the average NH4 concentration of the HT soil was 6.61 ppm and the OF soil was 4.36 ppm. This showed that the 2012 average HT soil ammonium concentration was 152% greater than the OF soil, which was similar to the original total N concentration difference between the two production systems from 2011. Data show that ammonium content of HT soil increased over the season, which was probably due to release of ammonium from organic matter mineralization.
The incredibly high NO3 levels during the spring could be explained by leftover NO3 built up over the winter from mineralization and a lack of nitrate uptake. The drop after week four was likely due to the installation of automatic irrigation in the HT. During the setup of the irrigation system, water was left on to test if the system worked. It was possible that enough water was put on to leach NO3 out of the soil sampling zone. The build-up in NO3 never occurred in the OF due to all the rain and melted snow.
The leaf tissue results were mixed, but there was either no difference or only a small difference between the production systems in leaf tissue N. Yet, the HT had more ammonium and nitrate during some parts of the year. Those results suggest that canes in the HT were taking up more nutrients, but using it to fuel a larger amount of growth than the OF canes, which would have diluted the extra nutrients over a larger amount of biomass.
Although the manure treatment applied the least amount of nitrogen of all the treatments, it had the largest amount of ammonium in the HT. It’s unclear why there were differences in soil ammonium amongst the treatments inside the HT, but not in the OF. This trend was repeated for available P, OM, and soluble salts. One conclusion from these results was that either effects from rain or lower temperatures were preventing decomposition of the organic fertilizers as well as leaching out nutrients.
Soil available phosphorous. Available P concentration was greater in the HT soil for every season. For three of the fertilizers, manure, mushroom compost, and the control, the HT had greater levels of available P. There was seasonal variation in the available P levels with spring and fall having greater levels than the summer There was no treatment affect for available P in the OF, but there was in the HT. Manure plots had the greatest available P amount. Mushroom and control plots had the second greatest amount of available P and were similar to each other. Fish emulsion and urea plots had the least amount of available P, were similar to each other, and were similar to all the treatments in the OF.
Greater P release rates of manure in the HT might have caused the greater available P content of manure plots compared to mushroom plots which had similar levels of P added. The greater available P levels in the spring were probably due to low uptake and buildup from mineralization over the winter. The greater amount of soil available P in the HT at the beginning of the trial led to higher rates in the soil however it was contributed to by the higher mineralization in the HT. The difference between the production systems in soil available P content was similar to leaf tissue P content.
Soil available potassium. During the spring, the HT plots had greater available K levels than the OF. For each cultivar x production system interaction there was seasonal variation of soil available K. Only during the spring was there a treatment effect on soil available K. Manure and mushroom plots appeared to have the greatest available K concentrations and were similar to each other. Differences in available K concentrations between fertilizers were not that large. The mushroom treatment added the most K to the soil, so it made sense that available K content was greater for those plots. The fish emulsion treatment added a similar amount of K as the manure treatment. The greater levels of available K in the HT soil during the spring could have been due to similar reasons as NO3 and phosphorous, low uptake during the winter. Available K was immediately available in a soluble form, so there was no build-up over the winter from mineralization.
Soil soluble salts. Soil in the HT had higher soluble salt levels than OF soil during the spring and fall. There was a treatment effect for soil soluble salt levels in the HT, but not in the OF. Mushroom compost plot had greater soil soluble salt levels than the urea and fish emulsion plots. Leaching occurred in the OF, which reduces the soluble salts. None of the values of soluble salts for the treatments or production systems was greater than the threshold of 1.0 dS/m for raspberries.
The results of this study demonstrate that there are clear differences between the nutrient dynamics in a high tunnel production system and an open field system. In a high tunnel, the rate of salt accumulation is often higher due to reduced leaching from precipitation. There are also differences between the organic fertilizers and the growers should select the product that is most suited to the conditions in the soil and the plant needs. It also demonstrates the importance of monitoring soil nutrients and plant tissue to determine the impact of different treatments. Although the high tunnel demonstrated significantly higher yields compared to the open field it did not require additional application of fertilizers. This is likely due to lower rates of leaching in the high tunnel and possibly higher rates of mineralization. The rate of application required may be higher with the removal of the plastic over the winter which would increase loss due to leaching. The higher temperatures in the tunnel would also likely lead to high rates of mineralization which could reduce nutrient reserves in the soil over a longer period of time. This study demonstrates the need to approach nutrient management in high tunnels differently from field systems, which will require increased monitoring to determine the optimal application rates for the system and to track changes in the nutrient composition of the soil in the high tunnel over time.
There was no economic analysis that was conducted in relation to this project due to the complexity of the project and the differences between each site. This research does demonstrate the need for growers to understand the specifc nutrient requirements that are needed for the proper management of nutrients in a high tunnel system. This does however demonstrate the need for farmers to ensure that they have an understanding of the nutrient dynamics in the high tunnel and how they differ from a field production system.
The results of this study provided some preliminary information about nutrient dynamics in organic high tunnel raspberry production systems. The establishment of specific recommendations was not possible due to the need for an increased number of sites and years of data collection, however it has provided growers with research based information to study the importance of utilizing soil and tissue testing to inform nutrient management decisions. Growers that were involved in the winter meeting expressed on surveys that the information provided on the nutrient management and yield of organic high tunnels would influence their decision making in the future. Based on discussions there was an increased appreciation of the value of tissue testing and the dramatic increase in yield observed in the tunnel.
Educational & Outreach Activities
1) Face-to-face learning. Through previous survey work, we have found that growers greatly appreciate the opportunity to gather with other growers for learning events. This provides the chance to have discussion regarding the content of the workshop or field day but also allows them to interact with other growers and to learn from each other’s experience.
Field Day 1- ‘Buliding your High Tunnel’ – This workshop was held in the early spring 2012 and gave growers the opportunity to come and gain hands-on experience constructing a high tunnel, a task that can be difficult if you have never done it before. This field day was held at the West Madison Agricultural Research Station (WM ARS) where the experiment is set up and was attended by 15 growers, technicians from the high tunnel manufacturer and extension staff. There was also discussion on irrigation system maintenance, tunnel sanitation and worker safety considerations.
Field Day 3 – ‘Late Season Extension’ – This field day will be held at the WM ARS and will focus on additional crop protection approaches to extend the season in spring and fall.
Seminar– ‘Organic High tunnel Raspberry Production’ – This workshop was held during the winter meeting and provided growers with information about nutrient uptake and availability, tissue and soil testing, the importance of a healthy soil. The goal is to help growers understand the factors critical to nutrient management and give them the tools to effectively and responsibly apply nutrients for optimal crop production and soil health.
2) Printed Resource Materials. The results of this project will be reported in both peer reviewed journal expected to be published in Fall 2014
Journal publication – ‘nutrient managment of organic rasberries in the high tunnel compared to the field.’
Trade publication – an ariticle is being prepared for the good fruit grower on the use of organic nutrient sources for high tunnel raspberry production
3) Online Resources. The UW fruit program website has been suspended since the departure of Dr. Harbut. The research results will be posted on a new website upon the position being filled.
Areas needing additional study
This study identified several areas that required additional research in regards to nutrient management in organic high tunnel systems. Specific areas that should be addressed include; the development of nutrient release curves for different sources of organic nutrients in the high tunnel throughout the growing season, impact of background nutrient levels on uptake and release rates of applied nutrients.