Russell Ranch Sustainable Agriculture Facility

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1 Russell Ranch Sustainable Agriculture Facility Research Report - Tomatoes March 2018 SUMMARY Russell Ranch Sustainable Agriculture Facility and the Century Experiment within it are entering into the 25 th year of research. The Century Experiment, a long-term cropping systems study, was originally designed to examine wheat, corn, and tomato productivity along irrigation and nitrogen rate gradients. However, in the quarter century following its initiation, the Century Experiment and the Russell Ranch facility as a whole has transformed into a hub for interdisciplinary teams of researchers from both public and private research institutions and companies to investigate questions centering around soil health, cover crops, crop nutritional value, irrigation management, remote sensing, and more. Many years of data have provided UC Davis researchers and the public insights into the effect of cropping system management practices on agroecosystem health, including crop yields, quality, and sustainable soil management. Russell Ranch has pioneered research into the soil health-building ability of compost through 24 years of research into certified organic management of corn and tomatoes in northern California. Societal demands placed on agriculture to fix and sequester increasing amounts of carbon from the air, labeled climate smart agriculture, have resulted in an expansion of interest in incorporating compost into agroecosystems and sustainable soil management. Implementation of the Healthy Soils Initiative by the state of California and the California Department of Food and Agriculture have only increased the need for growers to understand the effects of incorporating compost into their crop production systems. This report contains the results of research currently being conducted at Russell Ranch examining soil microbial communities and activity, crop productivity, and pest pressure that compare aspects of organic systems receiving composts to conventional systems receiving mineral fertilizers. A consensus is emerging in the literature that points to compost as a key component of sustainable soil management and stable crop yields. RUSSELL RANCH RESEARCH UPDATE 1

2 CROP YIELDS AND QUALITY The long-term Century Experiment at Russell Ranch compares tomato yields among three management systems employing corn tomato rotations that differ in organic inputs: 1) a conventional system receiving mineral fertilizer and winter fallow, 2) a hybrid system receiving mineral fertilizer and winter cover crops, and 3) a certified organic system receiving 4 tons/acre poultry manure compost annually and winter cover crops. All systems were furrow irrigated until 2013, when subsurface drip irrigation was installed to reflect modern management practices. Across 24 production years, tomato yields were similar among the conventional, hybrid, and organic systems (Figure 1), a result that runs contrary to the assumption that organic management is associated with lower crop yields. Tomato yields increased over time, but yields increased at a greater rate (1.25 tons/acre/year) in the conventional and hybrid systems receiving mineral fertilizer, compared to the organic composted system (0.75 tons/acre/year). Tomato yield variability was greatest in the hybrid system, followed by the conventional system, and was lowest in the organic system, relative to 24-year system averages (Figure 2). Tomato soluble solids content was greater on average by 0.35 percentage points in the systems receiving mineral fertilizer compared to the organic system receiving compost (Figure 3). However, the lower variability exhibited in the organic system tomato yields also appears in the organic system soluble solids content (Figure 3). The stark differences in yield and soluble solids variability over time among systems receiving mineral vs. organic fertilizer (compost) suggest that organic matter inputs like compost contribute to more stable soil fertility and structure, which could buffer environmentally induced stress effects on crop plants. Research into compost effects on soil structure that contributes to water-holding capacity has just been initiated, to investigate whether organic matter inputs like compost improve soil water infiltration and water-holding capacity, which could reduce irrigation requirements. 55 County average Figure 1. Tomato yields at the Russell Ranch Century Experiment over 24 years, from 1994 to 2017, in a conventional system receiving mineral fertilizer inputs and no winter cover crops ( Conventional ), a conventional system receiving mineral fertilizer with winter cover crops every year ( Conventional + WCC ), and a certified organic system poultry manure compost with winter cover crops every year ( Organic + WCC ). RUSSELL RANCH RESEARCH UPDATE 2

3 Period 1 Period 2 System average System average Figure 2. Normalized tomato yields (relative to the system averages per time period) at the Russell Ranch Century Experiment over 24 years, from 1994 to 2017, in a conventional system receiving mineral fertilizer inputs and no winter cover crops ( Conventional ), a conventional system receiving mineral fertilizer with winter cover crops every year ( Conventional + WCC ), and a certified organic system poultry manure compost with winter cover crops every year ( Organic + WCC ). Figure 3. Tomato soluble solids content, in percent, from PTAB analysis of tomato fruit harvested from a conventional system receiving mineral fertilizer inputs and no winter cover crops ( Conventional ), a conventional system receiving mineral fertilizer with winter cover crops every year ( Conventional + WCC ), and a certified organic system poultry manure compost with winter cover crops every year ( Organic + WCC ). RUSSELL RANCH RESEARCH UPDATE 3

4 CROP NUTRITIONAL VALUE Tomato fruit tissue has been archived annually at Russell Ranch since the Century Experiment s inception in UC Davis Food Science researcher Dr. Alyson Mitchell analyzed six years of tomato tissue, grown over the period of a decade, from the organic and conventional systems for α-tomatine content, a secondary plant metabolite produced by Solanum plant species to protect the plant against insects and disease. Tomatine compounds, when consumed by humans, are considered beneficial for human health due to their immune-enhancing and anti-cancer properties. As production of α-tomatine in tomatoes is likely to be affected by soil fertility, it was hypothesized that α-tomatine levels differed among conventional and organic systems, and that these differences on a large scale could affect human health. Dr. Mitchell s research found that α-tomatine levels were greater on average over 10 years in the organic system receiving poultry manure compost, compared to the conventional system receiving mineral fertilizer. These results suggest that organic management with compost application creates soil fertility conditions that may enhance tomato nutritional value for human consumption. More research in this area is needed to explore the effects of organic management and compost application on other fruit nutritional compounds. Figure 4. Comparison of α-tomatine content (µg/g dry weight) in organically and conventionally grown tomatoes from 1994 to Means with same letters are not significantly different. Adapted from the work of E. Koh, S. Kaffka, and A. Mitchell, UC Davis. For more information, see Koh, E., Kaffka, S., and Mitchell, A.E A long-term comparison of the influence of organic and conventional crop management practices on the content of the glycoalkaloid α-tomatine in tomatoes. Journal of the Science of Food and Agriculture 93: RUSSELL RANCH RESEARCH UPDATE 4

5 SOIL MICROBIAL COMMUNITIES Soil sampling was conducted in the top foot of soil in 2017 after 24 years of management to compare soil microbial community attributes among the conventional system receiving mineral fertilizer with winter fallow, the organic system receiving compost and winter cover crops, and a five-year-old managed native grass stand. Soil total nutrient content (organic and inorganic nutrient forms) was greater in the organic system than the conventional system, and total carbon and nitrogen were similar among the organic system and the grassland (Figure 5a-c). However, there is some evidence of phosphorus loading from repeated compost applications in the organic system (Figure 5b), a common trend in soils receiving annual additions of manure-derived fertilizer. Microbial biomass (the quantity of living microbes in the soil) was greater in the organic system than the conventional system and comparable to native grass soils. Mycorrhizal fungal abundance (fungi that form symbiotic associations with plant roots and increase plant access to soil nutrients and water) was also greater in the organic compared to the conventional system, but was lower than the grass soils, likely a result of the repeated tillage applied to the organic system for weed control. Potential nitrification (conversion of ammonium to nitrate, the form of nitrogen most often taken up by plants) was also greater in the organic system than the conventional, pointing to greater release of plant-available nitrogen from soil organic matter in the organic system. a) b) c) GRASS ORG CONV GRASS ORG CONV GRASS ORG CONV d) e) f) GRASS ORG CONV GRASS ORG CONV GRASS ORG CONV Figure 5. Soil total nitrogen (a), soil total phosphorus (b), soil total carbon (c), microbial biomass (d), relative arbuscular mycorrhizal fungi abundance (e), and potential nitrification (f) in surface soils of a native grassland ( GRASS ), organic system ( ORG ), and conventional system ( CONV ) at Russell Ranch in Adapted from the work of Franz Bender, scientist at UC Davis and UC Berkeley. RUSSELL RANCH RESEARCH UPDATE 5

6 SOIL CARBON Microbial biomass carbon (carbon content of the total microbial biomass measured in the soil), an important contributor to soil carbon stocks, was also 50% greater in the organic system compared to the conventional system (Figure 6). Soil carbon content is a soil characteristic that has received newly intensified interest due to carbon sequestration and climate smart agriculture initiatives, and poultry manure amendments appear to play a large role in building soil carbon stocks. Soil carbon was also measured at five depths down to 6 feet in upon initiation of the Century Experiment in 1993 and was repeated in 2012 to capture 20 years of soil change among cropping systems. Soil carbon change in the organic system was positive and greater than the conventional system with winter cover crops (Figure 7). Across the soil profile (0 to 6ft), soil carbon concentration in the organic system receiving poultry Figure 6. Microbial biomass carbon at two sampling depths, to a total depth of 1 ft., sampled from the organic system receiving poultry manure compost and the conventional system receiving mineral fertilizer, at Russell Ranch in Adapted from the work of Deirdre Griffin, PhD candidate at UC Davis. manure fertilizer increased by 1.13% per year, and soil C stocks increased by 0.6% each year (1.09 t/ha/yr), compared to no increase in the conventional + mineral fertilizer and winter fallow system ( conventional ), and the conventional + mineral fertilizer and winter cover crops ( conventional+wcc ) (Figure 7). Figure 7. Change in soil carbon concentration (left) and soil carbon stocks (mass; right) from 1993 to 2013 in Century Experiment systems at Russell Ranch. Shown: the conventional (Conv) corn-tomato w/ chemical fertilizer, the hybrid (Mixed) corntomato w/ chemical fertilizer and winter cover crops, the organic corn-tomato (Organic) with compost addition, and the conventional wheat-tomato (Wht/Tom) with chemical fertilizer. RUSSELL RANCH RESEARCH UPDATE 6

7 PEST PRESSURE Application of organic materials like poultry manure compost to soils generally increases soil microbial activity, which can confer pest control benefits by suppressing belowground pathogens that cause disease in plants. Also, as discussed above, compost application can alter soil fertility status and affect plant synthesis of secondary compounds that protect the plant against feeding insects. To investigate these relationships, UC Davis agroecosystems expert Dr. Amélie Gaudin collected tomato leaves from organic and conventional fields at three local farms and Russell Ranch and analyzed content of the plant secondary defense compounds salicylic acid and jasmonic acid in the tomato leaves. Results suggest that organically grown tomatoes receiving poultry manure compost at Russell Ranch had greater levels of both salicylic acid and jasmonic acid, compared to conventionally grown tomatoes receiving mineral fertilizer (Figure 8a,b). These trends corresponded with leafhopper counts, where greater numbers of leafhopper pests were measured in the conventional system than the organic system at Russell Ranch (Figure 8c). C) Figure 8. Secondary defense compounds in leaves collected in organic and conventional tomato fields at three farms and Russell Ranch ( Farm R, Farm RR ), salicylic acid (a) and jasmonic acid (b) content, and number of leafhoppers collected in sweepnets in each system (c). Adapted from the work of Dr. Amélie Gaudin, UC Davis, Department of Plant Sciences, agaudin@ucdavis.edu. RUSSELL RANCH RESEARCH UPDATE 7

8 CONCLUSIONS Poultry manure compost addition has been a key component of the organic system in the Century Experiment at Russell Ranch since its inception in 1994, and has been applied before corn and tomato every year since. Twenty four years of data demonstrate that compost application maintains tomato yields in organic systems at levels equal to conventionally fertilized systems, a result that runs counter to the popular narrative that organic systems yield lower than conventional systems. It is likely that the use of poultry manure compost as a fertility source in the organic system is the lynchpin of productivity parity between the organic and conventional tomato production systems at Russell Ranch. Beyond productivity comparisons, recent research results also support the application of poultry manure compost to build soil carbon and contribute to soil and human health. Organic management with annual poultry manure compost application increased levels of an anti-cancer compound in tomato fruit, pointing to a connection between organic inputs and fruit nutritional value. Poultry manure compost application also may increase the tomato plant s defenses against feeding leafhopper pests, which decreases risk of leafhopper-vectored diseases and contributes to greater fruit quality at harvest. Further linkages were observed between poultry manure compost application and soil health parameters, including microbial biomass, fungal abundance, soil nitrogen cycling indicators, and soil carbon. The levels of soil carbon accumulation observed only in the organic system receiving compost at Russell Ranch suggest that annual compost application to agricultural lands may be one of few viable options to increase carbon sequestration in agroecosystems. Research projects with poultry manure compost at Russell Ranch are thriving. Investigations are ongoing to address new questions, including: Does compost application increase soil water-holding capacity and decrease irrigation requirements? What are the mechanisms of pathogen and pest suppression in organic systems receiving poultry manure compost? And, what relationships exist between these soil health parameters and crop productivity? University of California researchers will continue to investigate benefits of compost to agriculture in California for many years to come. We would like to express our gratitude to Foster Farms for their ongoing support of research at Russell Ranch through annual donations of poultry manure compost to Russell Ranch. RUSSELL RANCH RESEARCH UPDATE 8