15 Year Mulch Study  - Our first talk is by Amaya Atucha. She's the Wisconsin Fruit Extension Specialist and she's gonna be talking about the 15-year mulch study.  - Thank you, Sara. I told her I really don't need any introduction. I'm playing local this time. The ones that don't know, I'm the new fruit crop specialist. I'd started a little bit more than a year ago. And today, I have a talk on some of my studies that I did as a grad student when I was at Cornell and the title of the talk, the real title of the talk is Orchard Floor Management Systems but Anna just put a little bit of her in the program and she changed it but we're gonna be talking about floor management systems today. So I think they are recording us so I'm gonna have to stay here.  There we go. 

So just first, an acknowledgment, all of the studies that I'll be showing today I said it was part of graduate studies and so, a big thank you to the Department of Horticulture at Cornell that supported me as a grad student, my adviser, Doctor Ian Merwin, and technical support from Mike Brown. Without them, I would have not been able to do any of this work. So just an introduction of why we are looking and why floor management and soil health which is that concept that we hear a lot is important. First of all, (clears throat) we know that it helps maintaining just the soil fertility, the soil tilth. It has an impact. The way that we manage our soil and our orchards has an impact on weed pressure and competition for water and nutrients. We all know with these new high-density systems, how we talk about how it's very important to control the weeds 'cause we want these tiny, little trees to grow fast and to fill up the space. Well, one of the reasons is because of our soil not nutrient and water competition. When we have a groundcover, we will have a mulch. Also, we know that that is going to have an effect on the soil temperatures and moisture extremes so days are very hot that soil probably is not gonna get that hot and their root system is not gonna suffer that much when we have a cover on our soil than when we have our soil completely exposed. 

Also, when we have specific groundcovers, we can provide a habitat for some beneficial insects and pollinators. And very important, in certain orchards with slope is to minimize soil erosion.  So what I'm gonna first present is a study. It's a long-term study on the effect of four groundcover management systems that it did on an apple orchard. And so, just the basic setting, what we did is over 17 years, we had four different ground management systems that I'll explain afterwards and we'll look at how the trees were growing, the nutrition of the tree production and we'll look at what was happening with the soil physical and biological properties.  So here are the four treatments that we had. We had a pre-emergence herbicide in which the soil was completely bare. We had no weeds. Nothing was growing underneath the trees. We had a post-emergence that you can see some weeds going on here. 

We had a mix of post-emergent herbicides. It was mainly glyphosate. We would apply twice during the growing season, early in May and then we would apply it again around July, August and so, some weeds would grow but during the times that we would apply the herbicide, the weeds would die. Then we had a sod treatment that it was just basically the continuation of the (clears throat) sod that we had on the alleyways. We just planted the same sod underneath the trees. And then we had a mulch treatment that was right underneath the trees in the same, all of these in the same area and that we would renew every other year. And so, a little bit more specifics about the treatments.  The variety that we had, this was an Empire on an M9, M11 planted in 1992. It was a three by six meters. That was the planting frame and we had as I said the four treatments. 

The PreHerb, the mix of pre-emergence herbicides. The PostHerb which was basically glyphosate as I say in May and July. The Mowed Sod which was a mix of just orchard grass. And then we had the mulch, it was a hardwood bark mulch composed of all these different species. And I said the orchard and the treatment were established in 1992 and were maintained since then. So what did we see during the time that we measure? And we'll look at these different treatments. So when we look at tree growth, you can see here the cumulative tree cross-sectional area in centimeters so it's basically the area of the main trunk.  So from 1992 all the way to 2008, we measured this and everytime you see this asterisk here, it means that there is a statistical difference. So you can see in the very first year, the blue and the red, so the first two columns are going to be the herbicide treatments then the green one is the grass and then the black one is the mulch. So what we saw is that during the first year, we saw some significant difference. 

With no surprise, the herbicide treatments, those trees were bigger so the first maybe four years, we saw that there was a significant difference in favor of using the herbicides. Trees were bigger. But as we move on and that's where these studies are so interesting, we start seeing that there's a shift on tree growth and we started seeing that the mulch, actually the trees on the mulch are much bigger and is statistically different from all the other treatments. And what we get by the last year, we can see how the mulch trees are significantly bigger than all of the rest. And we can see actually, that is the tree in the PreHerb or the pre-emergence herbicides, the treatment that was bare soil. Those trees are significantly smaller than the rest especially than the mulch which was very different from the trend that we saw the first four, five years. So this is very interesting because most of the studies that we do in orchard systems, we usually do four, five years and we're like, "Wow, that's a lot of years." Well, this shows that there are significant changes in trends when you keep measuring things like different treatments of groundcovers or different soil management systems.  So when we look at, we excavated one tree and we decided to divide it and look at what was the weight of the main trunk, of the main roots, of the secondary roots, and of the fine roots but we also look at if there was any difference in the trees itself in terms of the size of the trunks, the main scaffolds, The three-plus-year branches, the two-year branches, and the one-year branches so when we look at these, we actually didn't see a lot of significant difference. This was 10 years after the treatments were established. What we mainly saw was a different on the secondary roots. 

We saw that it was actually in the treatment that has the glyphosate applied twice during the growing season. We saw in that one and the mulch a little bit more roots than on the sod and on the bare soil treatment, and this is probably due to competition also. It might be possible in the sod that there were less secondary roots because of competition with the sod itself but in the case of the pre-emergence herbicide where we started seeing at this time and if you remember the previous graph, the tree started to decline in term of growth and so, what probably we're seeing here is that the sod properties are starting to deteriorate and that is affecting the development of the root.  When we look at yield, here we have the kilograms for tree...  starting from 1994 all the way to 2008, again, we see that in the very first years is actually the two herbicides so that the first two columns, that had the highest yield which, you know, it makes sense. We had bigger trees. They had bigger trees of higher yields at the very beginning but then once again, we started seeing that there's a lot of shift. There's some years that we had spring frost so that's why you see this very low yield here but we see that overall, after 17 years, there's not really a clear significant difference. You can see some trends. You can see that the mulch still produces consistently higher than the bare soil treatment and is actually the PostHerb so the glyphosate applied twice a week letting some of the weeds grow that is very comparable to the mulch so once again, this illustrates that what happens at the very beginning might not be what we see in a mature orchard afterwards. 

 So what happens with soil fertility? I know there's a lot of data here but I just want to point out some very specific things.  We measured here, we have 1992, '93, '95, 2000, 2005, 2006, and 2007. So by 2007, one of the biggest difference is that if we look at the phosphorus, a significant different mulch had 10 times more phosphorus in the soil. The same if you look at calcium, how much higher and significantly higher mulch is after those 17 years. And then the pH, we see some difference also in the pH. We tend to have a little bit higher pH on the mulch which was significantly different and we see some difference, significantly difference on the magnesium. So what happens that over time, that mulch that we kept putting on and putting on and putting on started decomposing and releasing a lot of these nutrients that just the bark of those trees had and thus, those were probably not available at the very beginning when we saw almost no significant difference but after 17 years of putting more and more and more mulch, what we saw is every time we would excavate the soil is this baked layer of like dark, dark organic matter, decomposed organic matter full of roots, all the roots were there. Well, no wonder, with all of those nutrients there and being moist and cool, of course, their roots wants to grow there.  When we looked at the carbon in the soil and the nitrogen and carbon-to-nitrogen ratio which is a good indication of microbial activity, we saw that the percent of nitrogen in the soil was significantly higher once again in the mulch with no difference on the other three treatments. When we look at the carbon, again, it's the mulch after those 17 years that it has, even before that, by '99, so seven years after the treatments were established, already the mulch treatment was significantly higher carbon content and the carbon-to-nitrogen content again was significantly higher for the mulch and there were no significant difference between the other treatments. 

 Some soil physical properties, some of the things that were measured by Oliveira in the same study, by eight years after the treatments were established is that you can see that the mulch treatment has a significantly lower bulk density so that soil was looser and more fluffy and nicer soil. We also see there's difference in the infiltration rate of the water and the soil capacity so that soil had a significantly higher water holding capacity. It had the capacity of keep more moist in that soil than the other treatments especially than their pre-emergence treatment, the treatment that had bare soil which we saw a little bit of compactation on the very top so a lower infiltration rate. This graph here shows soil biological properties so it's showing microbial activity in the soil which is very important for mineralization as you know and so, on the very top, it shows soil respiration. It's a good indication of how much activity that soil has, how much microbial activity is happening and so, you can see, this is a work done by Yao in 2005 in the same orchard, you can see that the mulch here, the first line with the Xs is significantly higher in terms of soil respiration than the other treatments. When we look at the number of bacteria, so in the colonies, the number of colonies of bacterias forming the soil, we see that the mulch also has significant and the PreHerb, the bare soil, very, very low bacteria activity and this counters for pathogenics and beneficials. And for fungi, once again, surprisingly, it's actually the grass that has a very significant, higher content of colonies of fungi in the soil compared with other treatments that were not significantly different so bottom line, we can see that the pre-emergent herbicide had a very, very low microbial activity on those soils.  So just a couple of summaries of these studies.  First, the total soil nitrogen, carbon content and the ratio of carbon-to-nitrogen  are essential for plant and nutrients and were much higher in the mulch treatment after 16 years than on the pre-emergence treatments or the bare soil treatment. We saw that in the weed-free plots so in the pre-emergence herbicides, most of the soil physical properties and biological activity was deteriorated. 

We saw that soil was much more compacted. It holded less water. It also has less roots and there was less microbial activity and it was actually the post-emergent herbicide so that glyphosate applies twice during the growing season, letting the weeds grow during the rest of the growing season which produced the best results in terms of compromising of soil fertility, soil microbial activity but also in terms of fruit production. That is what we are very much interesting. This is very nice but if we don't produce any fruit, it doesn't work.  So the second study that I'm going to present today is a study in which we look at the entire system. We wanted to know, given that we have all of these treatments...  what happened with the nitrogen budget? What happens with the nitrogen in the system once you have a groundcover management system established for so long? So the objectives were, mainly, we were concerned about pesticides and fertilizer, excessive use and leeching into the groundwater which was a problem that we had in upstate New York so the idea started from there. We wanted to try to look, "Well, if we treat the soil differently, "we manage our weeds differently, "can we affect the overall nitrogen budget "of the sod of the plant "given that we have all of these previous information?" So we quantified the inputs and the outputs of nitrogen in the orchard with these four different treatments which are going to be the same treatment. In one year in which we apply fertilizer and in a year in which we did not apply any fertilizer so in the year that a fertilizer was applied, 53 pounds of nitrogen per acre were applied. 

So again, the same treatments, two years: a year with fertilizer and a year without fertilizer. So what did we see? Or how did we measure it? This is our little budget so we look at everything that was adding nitrogen to the system: the fertilization, all the nitrogen that was coming from the irrigation and precipitation water, and the nitrogen that was being mineralized from the bark mulch, from the treatment that had the mulch. We look at everything that had internal fluxes so all of the nitrogen that was being used and coming back to the system, just in the surface, all those weeds, all the grass, we would basically clip that grass and the grass would stay there, decomposed, and the nitrogen would just go from the grass to the soil, from the grass to the soil, and it would stay there. We measured that. We measure how much nitrogen was being recycled through the leaf litter, through the pruned wood, and we calculated how much nitrogen was coming out of the soil. Then we look at the outputs, how much nitrogen we were taking out of the system through the fruit and all the nitrogen that was going out through the water that was leeching all the way out of the orchard and the surface runoff water that had also nitrogen.  So just to show you more or less how we did these things. So this is how we measure all the nitrogen that was coming out from surface vegetation. We had these litter bag studies in which we would clip some of the vegetation on top, put it on these special bags, and measure over time from day zero, how much nitrogen they had until several days afterwards to see how much of the nitrogen had been decomposed by the microbes in the soil and going back to the soil so that's how we measure that.  One second. 

 This is how we measure the amount of nitrogen in the leaves so what we did is we chose one tree, we put a big net, we cut all of the leaves from those trees, we dried them, we measured them, and we took a sample, and we analyzed how much nitrogen it had so that's how we measure how much nitrogen there is in the leaves which was a lot of work.  And then we measure the outputs. Fruit, very easy, of course, we measure every single fruit that we had. We took a sample and we analyze how much nitrogen was there so that we can take it out of the budget. The subsurface leeching, what we did is we had this system in which each one of the plots, these are each one of the plots, we had 12 plots, was hydrologically isolated and we had some pipes, some drainage pipe that would capture all of the water. It was probably three to four feet under the ground and it would take us to these stations in which we could collect some water there and we had a little system of some tipping buckets that were connected to a data logger so all of the water that was infiltrating the soil was being collected on these pipes and being driven to these tipping buckets that you can see here that when they're full, they switch, they flip like this and so, you know the exact volume of water that you have in there and so, if you have the number of tips, you know how much water run over when there was a storm or when we irrigate it, we could calculate that and we would take periodically samples of that water and analyze how much nitrogen it had. And so, then we calculated all of the nitrogen that was lost through the leeching so the water that was infiltrating the orchard. In a very similar way, we measured the water that was exiting the orchard through surface runoff. We had a system in which we had half a pipe on the bottom of this plot and it would collect all of the water running from the surface and it would once again go to a tipping bucket and then we would do the same as we did with the leeching.  So what did we see? You can see on the graph on your left side is an F for the year that we fertilized it with nitrogen and NF for no fertilizer so here, what we have is the amount of nitrogen that was being mineralized from what was growing just on the surface of the soil so here are the grams of nitrogen per kilogram biomass so this is those little packs that we had that we put these litter bags that we put and we can see that in the year that we applied fertilizer, these solid squares here show the mulch. 

It shows how the mulch mineralized much more nitrogen so that vegetation, those weeds that were growing in the mulch had a lot of nitrogen and if you cut them down and you let them mineralize, they were going to put a lot of nitrogen in the system. The year that we had no fertilizer, we still saw that the mulch was the one that was releasing the most nitrogen from that surface vegetation. Just because the mulch was also given nitrogen to the system so if you had the weeds growing where there was a lot of nitrogen, well, those weeds contain a lot of nitrogen as well.  When we look at the average concentration of nitrogen that was coming out of the runoff water, you can see that in the year with fertilizer, here are the treatments. The treatment with bare soil had the highest concentration of nitrogen exiting the system through runoff.  While the year that, when we look at the leechate, we actually saw that it was the mulch in both year that has significantly higher nitrogen exiting the system so what this means is basically there was more nitrogen coming out through runoff on the bare soil because the bare soil, as I was showing before, had lower infiltration of water. The water was just running off instead of coming in because there was this crust that formed because we had had it exposed for so long. It had nothing to protect it while the mulch, there was a lot of water actually infiltrating the mulch because it had a much higher porosity, the water would go into the soil and it would drive all of this nitrogen coming out of the mulch after 17 years and that's why we saw these really high concentrations. And so, when we look at the water flow, once again, we see that the mulch had the lowest amount of surface runoff because all of the water was infiltrated but it had the highest level of leeching water because more water was coming in and going through the soil profile and then exiting to the groundwater. So, again, this is a lot of data but what I really want to show is up here, there are all the treatments: the bare soil, the glyphosate, the sod, and the mulch. 

And here's the budget, you can see this is the everything that was exiting, all the nitrogen that was exiting the system out of the orchard, all of the internal fluxes, and all of the outputs. So you can see here the mulch, it has a significantly higher input. There was a lot of nitrogen going into the system when we had a mulch, either basically from the decomposition of the mulch. When we looked at the balance which is basically if you add what you take out,  sorry, what you put in weed where it was being recycling and you subtract what you're taking out, overall, what we saw is that the year that we had fertilizer so it's the first column for each one of these: the 20, 10, 43, and 187, they were all positive which basically means that orchard had more than enough nitrogen. The nitrogen that we were putting in with the nitrogen that we were taking out, it was a positive result. There was extra nitrogen than what the orchard really needed. But the year in which we apply no fertilizer, you can see that both of the herbicide treatments have negative number. It means that there was more nitrogen being lost in that orchard so there was not enough nitrogen.  But with the groundcover and with the mulch, the year without fertilizer is still positive which means that those systems, after 17 years, in a way, they had equilibrated and they were given enough nitrogen for those trees to grow, to produce and there was less nitrogen being lost out of the system and this happened after 17 years of those treatments. Okay, I only have three more minutes so we're gonna go fast through the summary. 

 The soil nitrogen that was mineralizing and recycling so basically everything that was coming from the leaves, from the pruning, from the surface vegetation, all of that accounted for over 60% of the nitrogen that was being recycled.  The harvested fruit represented more than 70% of the nitrogen that was coming out of the orchard so even nitrogen was coming out through runoff and through leechate and through the fruit that we were harvesting, 70% of the nitrogen was coming out with the fruit.  Most of the nitrogen's losses occur through leechate rather than runoff so this was a big eye-opening for us because it meant there's a serious potential contamination of groundwater because a lot of the nitrogen was just being leeched out of the system.  As I said, there were positive balance overall for the sod and the mulch but it was not the case for the herbicides.  And potential long-term problems with the nitrogen leechate in the orchards that made us think that maybe if you are applying organic amendments like compost or you're using mulch or you're using any other source of organic nutrient that you should be cautious about how much you put in and how often you're putting it because you might ended up what would happen with us with the mulch, that that mulch was being mineralized and there was so much nitrogen coming out of that that there was a lot of nitrogen going into the groundwater which is a big problem. And overall, after 17 years, the system was not balanced for the two herbicides and we saw that the main reason was that the recycling of the nitrogen was much lower when we were having an herbicide compared when we had the grass or when we had the mulch.  So with that, I think that I'm running out of time. I'll be happy to take any questions.  No, it was clay. It was mainly clay.