Recipient Organization
UNIVERSITY OF CALIFORNIA AT SANTA CRUZ
1156 HIGH STREET
SANTA CRUZ,CA 950641077
Performing Department
(N/A)
Non Technical Summary
Phosphorus (P), an essential element for growth and development, is taken up by plants as phosphate (Pi), however Pi is unevenly distributed and relatively immobile in soils. As a result, more than 30% of the world's arable land requires the application of P fertilizers for cropping and many natural ecosystems are P limited. Unfortunately, part of the applied P in intensive cropping systems can enter the waterways through runoff and erosion, contributing to pollution and eutrophication of surrounding groundwater, lakes and coastal environments. Tracking P cycling, mobility in soils, and determining soils' P availability to plants is challenging because adsorption/desorption, immobilization (occlusion by or precipitation as minerals), mineralization (conversion of organic P compounds to Pi), and uptake (by organisms) all occur simultaneously in the soil. Determining soil P availability and mobility and how these characteristics vary with soil type and agriculture practices will help reduce P loss from agriculture systems and contribute fundamental understanding to inform science based management plans.A clear understanding of all aspects of soil P biogeochemistry is required to determine P availability and mobility in soils, but analytical techniques have not been available to fully characterize P cycling in soils. We developed a natural isotopic tracing procedure of oxygen in phosphate to (d18Op) to track P sources and biological cycling in soils. We propose to apply this procedure to study P cycling in various agriculture soils representing an array of farm management practices. Work will take place at the Russell Ranch Experimental LTRAS, a long-term comparison of 10 conventional, organic and alternative cropping systems, both irrigated and non-irrigated is taking place.We expect that different processes will dominate P cycling in different soil types (soil pH, grain size, mineralogy, organic matter content, etc.) and under different management and farming systems (no tillage, and use of organic--plant residue and/or animal waste--vs. inorganic fertilizers). These processes will ultimately determine the availability of P to plants and the potential for P loss from the system.
Animal Health Component
20%
Research Effort Categories
Basic
70%
Applied
20%
Developmental
10%
Goals / Objectives
The major goal of this project is to use stable isotopes of oxygen in soil phosphate (d18Op) to determine the impacts of different farming and management practices on P cycling in soils and P availability to crops. This will be done using plots from the Russell Ranch Sustainable Agriculture Facility thus elucidating how P availability, loss and transformations relate to soil characteristics and farming practices and provide a foundation for making science based management plans that would help achieve sustainable production of ecosystem services.
Project Methods
In this research, we intend to use innovative state-of-the-art techniques combined with traditional methods to study the fate of P in soils representing different farming practices. To quantify the P fractions and distinguish between WSP, labile P (slightly bound), strongly adsorbed and precipitated P, which are important both for agronomic management and environmental protection we will use sequential P extraction methods, (e.g., Hedley et al., 1982; Tiessen and Moir, 1993). To shed light on the biogeochemical processes that control the transformation, movement, and storage of P in soils we will employ d18Op analyses to the different soil fractions. This information will be related to farming practices and along with ancillary data on soil properties will contribute to the construction of a unifying soil P biogeochemical cycling model under different farming practices.Soil P cycling will be investigated using d18Op associated with various soils fractions in samples from well studied plots from the Russell Ranch Sustainable Agriculture Facility (LTRAS) representing different long term farming practices including different crop rotations, irrigation and nitrogen application (Figure 3). Not illustrated in Figure 3 are the three tomato rotations (organic, conventional and the "mixed" systems) which all had different P inputs. The "mixed" has been managed as a hybrid of conventional and organic. The conventional has 45 lbs P in pre-plant fertilizer applied per year, while the "mixed" has had 45 lbs P applied every other year. The organic receives phosphorus from chicken manure compost and has an average 87 lbs P/yr applied. In addition, from 2003-2007 treatments with conventional vs. reduced till took place. Soil from the 16 different treatments (8 treatment combinations applied to two crop types) will be sampled twice during the first year of the project before seeding and during harvest. In addition the fertilizer and manure used, drainage water and crop residue will be sampled. In the second and third years, in collaboration with LTRAS personnel, different types of P additions will be applied in micro-plots within each main plot and these mirco-plots and the main plots will both be sampled during harvest season. In year 2 we will apply manure and conventional inorganic fertilizer and in year three compost and organic conventional fertilizer. Depending on results we may also test different types of manure (chicken, horse, etc.) and/or different amounts of P additions. In total the samples from the mini-plots will add 64 distinct samples in years two and three.Farming practices induce alterations in physical and chemical soil properties leading to differences in distribution of minerals and organic compounds in soil. Different soil fractions contribute differently to cycling and availability of P in soil (O'Hara et al., 2006; Solomon and Lehmann, 2000). P source used for fertilization, amount of P applied, application timing, crop type, irrigation, cultivation, and harvesting processes were all shown to influence concentrations of both Po and Pi and their association and distribution in soils (Syers et al., 2008; Solomon and Lehmann, 2000). Combining the modified Hadley chemical P fractionation and the stable isotope tracing procedures will yield important insights regarding cycling and transformations of P in soil and how they relate to farming practices.Ancillary data including soil quality measures, soil temperature, moisture and d18O of soil water, organic C content, metals associated with P in soil (Al, Fe, Ca), microbial biomass and P-enzyme activities will also be collected. Additional data from these well studied sites(such as soil type, mineralogy, texture, physical properties, organic matter content, C and N, pH, solute composition, nematode counts, etc.) will be assembled from the LTRAS data set and used to assist in interpretation. All of the above data will be used to construct a unifying model to explain P cycling is soils as they relate to soil properties and farming practices and to delineate the transformation, bioavaiability and various physical, biological and farming impacts on the P cycle. More details on the LTRAS could be found on the Russell Ranch Sustainable Agriculture Facility web page (http://ltras.ucdavis.edu/)