Combinatorial biosynthesis has been successfully applied to generate a library of fungicidal antimycin analogs, which are cytochrome C reductase inhibitors; fenpicoxamid for instance has been developed by Dow AgroSciences to control the wheat pathogen Zymoseptoria tritici. Based on detailed understanding of the bio-synthetic pathway of antimycin, diversity-oriented biosynthesis of about 400 analogs was achieved by altering the chemical identities of priming, extending, and tailoring building blocks. Several of these analogs exhibited stronger biological activities than the original NPs, while a few introduced orthogonal reactive handles in the molecules that enabled further chemical derivatization.The application of insecticides, herbicides, and fungicides with potent bio-activities and good safety profiles has played an indispensable role in improving the yield and quality of agricultural products. However, their continuous and excessive use has led to the emergence of resistance among plants and plant pathogens. Resistance gene-directed NP discovery has been demonstrated to be an effective strategy to uncover novel NPs with desired modes of action as lead candidates for new insecticides, fungicides, or herbicides to address the problem of growing resistance. Metabolic and bio-synthetic engineering of NP synthetic pathways in yeast can further improve titers for microbial production and biological activities for commercial applications. The increasing sophistication of these tools means that we are entering a renaissance of NP discovery for both pharmaceutical and agricultural applications.The Pajaro River and Elkhorn Slough watersheds on California’s Central Coast include some of the state’s most productive and highly valued agricultural lands. The watersheds’ streams and rivers serve as key municipal and agricultural water sources, recreational areas, and wildlife habitat.
Both watersheds drain into Monterey Bay, a nationally protected marine sanctuary,blueberry grow pot and water from the Elkhorn Slough watershed passes through Elkhorn Slough, the largest tidal salt marsh along the Central Coast and a critical resource for resident and migratory birds, fisheries, and other wildlife. Agricultural and urban land uses in the Pajaro River and Elkhorn Slough watersheds have compromised the quality of their waterways. Two nutrients, nitrogen and phosphorus , are of particular concern. High levels of nitrate-N in drinking water pose a threat to human health, and both nitrogen and phosphorus are linked to excessive growth or “blooms” of algae and other plants that can decrease the amount of dissolved oxygen in waterways below the levels that aquatic organisms need to survive. As part of state and federal efforts to protect and restore water quality, regulatory agencies have been charged with establishing target concentrations for pollutants in waterways that will protect beneficial uses1 . The Central Coast Regional Water Quality Control Board has set a preliminary target of 0.12mg/L for soluble reactive phosphorus concentrations, based on the lowest concentrations they have observed in waterways of the Pajaro watershed with excessive plant or algae growth. This pollution is thought to come primarily from “non-point” sources, which are unregulated discharges from urban and agricultural land uses.Increasing evidence suggests that crops cannot take up all of the phosphorus fertilizer being applied ; as a result, excess phosphorus accumulates in the soil. High levels of soil phosphorus in turn lead to higher phosphorus levels in water draining from agricultural fields . In the Pajaro River and Elkhorn Slough watersheds, high concentrations of phosphorus have been identified in several waterways. The RWQCB Watershed Management Initiative implicates agriculture as the primary source of this and other nutrient pollution . However, little empirical data exists to demonstrate that agriculture is responsible for nutrient loading into these waterways. In this research brief we present data from water quality monitoring conducted between October 2000 and September 2004, to demonstrate the way that agricultural land use influences phosphorus concentrations in streams and rivers.
We discuss the nature of phosphorus pollution from agriculture along the Central Coast, examine the implications of these data for agricultural regulations, and offer suggestions for reducing phosphorus losses from farmlands.The Pajaro River watershed drains approximately 1,300 square miles of land, with 7.5% of the watershed in agriculture. Agricultural activities are concentrated in three productive areas: on the flood plain of the Pajaro River near the towns of Watsonville and Aromas ; in South Santa Clara Valley near Gilroy and San Martin ; and in the San Juan Valley near San Juan Bautista and Hollister . Production near the coast is dominated by cool-weather vegetables, berries, flowers, and apples. In the warmer inland areas—east of the Santa Cruz and Gabilan ranges—growers rotate crops of cool- and warm-weather vegetables, along with grapes, flowers, and stone fruits. Approximately 70 square miles in size, the Elkhorn Slough watershed drains northern Monterey County and a small portion of San Benito County. Approximately 24% of the watershed is in agriculture , with strawberries and cool-weather vegetables making up the majority of cultivated acreage .To assess the role of agricultural land use on phosphorus levels in waterways, we began sampling two creeks in October 2000 in the Elkhorn Slough watershed , and several waterways in the Pajaro River watershed, including Corralitos Creek, Watsonville Slough, the Pajaro River, and publicly accessible agricultural drainage ditches. In October 2002 we expanded the project to include all tributaries of the Pajaro River to determine the proportion of nutrients each water basin contributes to the river. We collected water samples every 2 weeks at approximately 60 sites throughout the watershed. Sites were selected to bracket agricultural activity and other land uses in order to compare concentrations upstream and downstream of potential nutrient sources. In addition, several locations were sampled more frequently to capture storm event variability and to measure water discharge for calculations of nutrient loads . For brevity we report here on several key sites that demonstrate spatial and temporal patterns we found to be characteristic of the entire watershed.Naturally occurring phosphorus is derived from apatite, a common mineral consisting of calcium fluoride phosphate or calcium chloride phosphate.
The availability of P to plants in any soil is limited by the rate at which apatite dissolves. Relative to other plant macro-nutrients, inorganic P is fairly insoluble and binds to soil particles. This means it is typically retained in the soil profile and doesn’t leach into groundwater. Phosphorus availability to plants is greatest when the soil’s pH is around 6.55–7.5. In acid soils, dissolved phosphate can precipitate with iron and aluminum oxides, making it unavailable to growing plants, whereas in alkaline soils, dissolved phosphorus can precipitate with calcium. Both inorganic and organic forms of P are found in soils. Since soils tend to “hold” P, it is most commonly lost from soils via erosion. However, if sufficient amounts of P are added to soils over time in the form of fertilizers or other inputs, all the attachment sites on soil particles can become filled, at which point the soluble form of P will be lost through runoff or by leaching. The amount of phosphorus lost from agricultural fields varies greatly,hydroponic bucket and is specific to both local environmental conditions and land management practices. Conditions that increase erosion, runoff, and subsurface water flow also increase soil P losses. Therefore, climate, soil type, and slope can all influence P losses. In addition, a number of nutrient and soil management practices impact soil P movement, including the amount of P applied in fertilizer, the solubility of applied P, the timing of fertilizer applications in relation to plant use and irrigation or rain events, the presence of artificial drainage systems, and cover cropping and tillage practices that affect erosion and water infiltration. In general, most soil P is lost via surface runoff and erosion, but the amounts lost and the timing of such losses are unique to the conditions and management practices used at each ranch or farm. For example, the use of tile drainage systems, which are common in parts of the Pajaro River and Elkhorn Slough watersheds, can greatly increase subsurface P losses. Drains can affect P movement and loss in different ways. As water moves through the soil profile toward the drain, the soil can bind dissolved P, thus removing it from the water; however, tile drains also reduce the amount of time P fertilizer is in contact with soil particles, so overall a smaller fraction of applied P may be retained in the soil profile . Tile drains have also been shown to transport significant amounts of particulate P from topsoil to surface waters during storm events .
Conversely, in soils with poor drainage, installation of tile drains can reduce total P losses during storms by improving infiltration and reducing P lost via surface runoff . Therefore, determining the role of tile drains in P transport under local soil and climate conditions is important for managing P levels in the Central Coast region. In addition to agriculture, natural processes and urban runoff may also contribute P to waterways. Small amounts of P are deposited from the atmosphere in rainfall and in dry airborne particulates. Urban sources of P include residential fertilizer use, automotive products, and septic tanks and leach fields. In the past, detergents were a significant source of urban P pollution, but most detergents are now phosphate-free. In aquatic environments, particulate P can convert to dissolved forms and increase the pool of reactive, dissolved P . These reactive forms, called orthophosphate or soluble reactive phosphorus , are readily taken up by algae, and in excess levels may lead to algae “blooms” and eutrophication .Geographical patterns of dissolved phosphorus concentrations suggest that levels are influenced by land features as well as land use practices. Soil characteristics such as a shallow water table are associated with elevated stream SRP levels, particularly in agricultural areas. In the south Santa Clara Valley, SRP concentrations were low in all waterways with the exception of San Juan Creek. The San Juan drainage has a shallow, perched water table, and receives discharge from artificial tile drain systems, used in agricultural fields to remove water from the rooting zone of crop plants. In contrast, Llagas and Uvas Creeks, which do not receive tile drainage, had low SRP concentrations at all sites. Median SRP concentrations increased slightly at sites downstream of agriculture , but exceeded the target level on fewer than 20% of visits . San Benito Creek and Miller’s Canal, which were both sampled near agricultural fields, also had low median SRP concentrations. The use of tile drainage systems may account for higher SRP levels in waterways with shallow water tables and agricultural land use, including Watsonville Slough and Corn Cob Canyon Creek. Tile drainage systems can increase phosphorus losses by increasing soil infiltration rate and reducing the amount of phosphorus that adheres to soil particles . During winter storms, tile drains may also act as conduits for particulate phosphorus, carrying eroded topsoil to waterways . Non-agricultural land uses, and occurrence of mineral types naturally high in SRP, may also contribute to elevated SRP concentrations in some areas. While nutrients were generally higher at locations downstream of agriculture, Corralitos Creek had elevated nutrients both upstream and downstream of agriculture. At the most upstream site , SRP concentrations often exceeded the target level of 0.12 mg/L while two other nutrients, nitrate and ammonium were very low. The elevated SRP levels are not likely from fertilizer or septic sources, which also tend to be high in nitrogen compounds, but may be due to the mineral composition of soils in this drainage and/or soil erosion. Comparisons of sites upstream and downstream of agriculture revealed higher downstream SRP concentrations in many waterways, providing evidence that agricultural land is a source of phosphorus in surface waters. In the Elkhorn Slough watershed, SRP progressively increased with the amount of cultivated acreage located upstream . The phosphorus content of the soils in the watershed may play a role in how phosphorus moves through this system, but this has not been looked at systematically. In Carneros Creek at Dunbarton Road, which is at the upstream edge of cultivated acreage, the median SRP concentration was 0.10 mg/L, and at San Miguel Canyon Road, downstream of several miles of farmland, the median concentration was 0.53 mg/L. However, in addition to row crops, land use along Carneros Creek is mixed with ranches and rural homes, and more intensive monitoring is necessary to partition nutrient inputs from these potential sources.