Organically produced fruit and vegetables are among the fastest growing agricultural markets. With greater demand for organically grown produce, more farmers are considering organic production options. Furthermore, there is an increasing interest in maintaining optimal production in an organic system, which involves appropriate nutrient management. The objectives of this review were to summarize the current state of our knowledge concerning effects of organic production systems on phosphorus (P) availability, describe P availability in common organically accepted P sources, and review best management practices that can reduce environmental risks associated with P management in organic systems. Organic production systems seek to improve soil organic matter and biological diversity, which may impact P cycling and P uptake by crops. Increases in organic matter will be accompanied by an increase in the organic P pool. Furthermore, management of cover crops and potentially enhanced arbuscular mycorrhizal fungi colonization from organic production practices can increase the availability of soil P pool (both organic and inorganic) by stimulating microbial activity and release of root exudates. This can help compensate for low soil P, but will not supersede the need to replace P removed by the harvested crop. Phosphorus fertilization in organic production systems entails balancing the P inputs with crop removal through selection and management of both nitrogen (N) and P inputs. Organic production systems that rely on manure or composts for meeting crop N demand will likely have a P surplus; therefore, P deficiencies will not be an issue. Systems using other N sources may have a P deficit, therefore requiring P supplementation for optimal plant growth. In such situations, maintenance P applications equal to crop removal should be made based on soil test recommendations. Primary organically approved P sources are phosphate rock (PR), manure, and compost. Phosphate rock is most effective at supplying P in soils with low pH (less than 5.5) and low calcium concentrations. Phosphate rock applications made to soils with pH greater than 5.5 may not be effective because of reduced PR solubility. Manure- and compost-based P has high plant availability, ranging from 70% to 100% available. Use of manures and composts requires extra considerations to reduce the risk of P loss from P sources to surface waters. Best management practices (BMPs) for reducing source P losses are incorporation of the manures or composts and timing applications to correspond to periods of low runoff risk based on climatic conditions. Organic production systems that use manures and composts as their primary N source should focus on minimizing P buildup in the soils and use of management practices that reduce the risks of P loss to surface waters. Evaluation of P loss risk with a P index will assist in identification of soil and management factors likely to contribute to high P loss as well as BMPs that can decrease P loss risks. BMPs should focus on controlling both particulate and dissolved P losses.
Nathan O. Nelson and Rhonda R. Janke
May Elfar Altamimi, Rhonda R. Janke, Kimberly A. Williams, Nathan O. Nelson and Leigh W. Murray
Greenhouse experiments were conducted to determine the response of Brassica oleracea L., pac choi to fertilizer rates and sources and to establish optimal soluble nitrogen (N) application rates and nitrate meter sufficiency ranges. Conventional soluble fertilizer was formulated from inorganic salts with a 4:1 NO3-N:NH4-N ratio. Phosphorus (P) was held at 1.72 mm and potassium (K) at 0.83 mm for all treatment levels. The organic soluble fertilizer, fish hydrolyzate (2N–1.72P–0.83K), was diluted to provide the same N levels as with conventional treatments. Both fertilizers were applied at N rates of 0, 32, 75, 150, 225, 300, and 450 mg·L−1. Seedlings were transplanted and fertilizer application began at 18 days. Plants were harvested at 7 weeks (5 weeks post-transplanting) after receiving 15 fertilizer applications during production. Samples of the most recently matured leaves were harvested weekly and analyzed for petiole sap NO3-N and leaf blade total N concentration. Leaf count, leaf length, and chlorophyll content were also measured weekly. Fresh and dry weights were determined on whole shoots and roots. Optimum yield was achieved at the 150-mg·L−1 fertility rate with both conventional and organic fertilizers. Field and high tunnel experiments were conducted to validate the sufficiency ranges obtained from the greenhouse studies. Sufficiency levels of NO3-N for pac choi petiole sap during Weeks 2 to 3 of production were 800 to 1500 mg·L−1 and then dropped to 600 to 1000 mg·L−1 during Weeks 4 through harvest for both conventional and organic fertilizers sources. Total N in leaf tissue was less responsive to fertilizer rate effects than petiole sap NO3-N. Chlorophyll content was not useful in evaluating pac choi N status. These guidelines will provide farmers with information for leaf petiole sap NO3-N to guide in-season N applications.
Sharon J.B. Knewtson, M.B. Kirkham, Rhonda R. Janke, Leigh W. Murray and Edward E. Carey
The sustainability of soil quality under high tunnels will influence management of high tunnels currently in use and grower decisions regarding design and management of new high tunnels to be constructed. Soil quality was quantified using measures of soil pH, salinity, total carbon, and particulate organic matter (POM) carbon in a silt loam soil that had been in vegetable production under high tunnels at the research station in Olathe, KS, for eight years. Soil under high tunnels was compared with that in adjacent fields in both a conventional and an organic management system. The eight-year presence of high tunnels under the conventional management system resulted in increased soil pH and salinity but did not affect soil carbon. In the organic management system, high tunnels did not affect soil pH, increased soil salinity, and influenced soil carbon (C) pools with an increase in POM carbon. The increases in soil salinity were not enough to be detrimental to crops. These results indicate that soil quality was not adversely affected by eight years under stationary high tunnels managed with conventionally or organically produced vegetable crops.
Sarah A. Masterson, Megan M. Kennelly, Rhonda R. Janke and Cary L. Rivard
The utilization of grafted tomato (Solanum lycopersicum) plants in the United States shows significant promise, particularly as intensively managed production systems like high tunnels and greenhouses become more popular. However, the availability of grafted plants in the United States is currently a major barrier and a large portion of farmers who would like to use grafted plants would prefer to propagate their own. The objectives of this study were to determine how healing chamber design affects graft survival and microclimate, and to investigate how scion leaf and shoot removal affects graft survival in various healing chambers. Similar experiments were repeated at two locations in Kansas and a split-plot, randomized complete block design (RCBD) was used in each, with three and four replications being conducted over time at each of the locations. Five chamber treatments were tested including a negative control (none) as well as shadecloth alone, white vinyl mesh, polyethylene film and shadecloth, and polyethylene film with shadecloth and a cool-mist humidifier. No statistically significant effects of chamber design were seen on grafted plant success. However, microclimate data from the various healing chambers offer valuable data toward determining the best management practices for grafted plants. Shadecloth alone showed significant promise as this covering provided cooler temperatures during the afternoon when the healing chambers were prone to excessive heat buildup. Three tube-grafting methods were tested, including standard tube-grafted plants (no leaves removed), leaf removal (LR) plants (≈75% of the leaf surface area was removed from the scion), and shoot removal (SR) plants (the apical meristem and all true leaves were removed). The SR method did not affect graft survival, but the LR method increased grafting success from 78% to 84% and was significant as compared with the other methods (P < 0.05). The long-term goals of this work are to develop successful propagation systems that can be used by small-acreage growers with limited greenhouse facilities. The data presented here indicate that high-humidity healing chambers (>85% relative humidity) may not be necessary for tomato, and LR can increase the grafting success rate.
Sarah A. Masterson, Megan M. Kennelly, Rhonda R. Janke and Cary L. Rivard
Grafting with interspecific hybrid rootstock is effective for tomato (Solanum lycopersicum) growers looking to reduce soilborne disease in the southeastern United States. However, production with grafted tomato has not been tested in the central United States, where soilborne disease pressure is low. Small-acreage growers would like to produce grafted plants themselves, but many have difficulty with propagation due to water stress in the scion postgrafting and/or high temperatures. Removing the upper portion of the scion to reduce leaf area during the grafting procedure [shoot removal (SR)] could help to reduce water stress postgrafting, but there are no data available that indicate what effect this practice has on tomato yield. Five high tunnel trials and one open-field trial were conducted in 2011 and 2012 to investigate potential yield effects related to the use of two rootstocks and SR during the grafting procedure. The implementation of grafting with rootstocks significantly increased fruit yield in five of the six trials (P < 0.05). The average yield increases by ‘Maxifort’ and ‘Trooper Lite’ tomato rootstocks were 53% and 51%, respectively, across all trials. SR during the grafting process may penalize tomato yield and our results suggest that rootstock vigor plays a role. Plants grafted with ‘Maxifort’ across all of the trials consistently increased shoot biomass in four of five of the high tunnel trials compared with nongrafted plants (P < 0.05), whereas plants grafted with ‘Trooper Lite’ rootstock increased shoot biomass in one trial. Similarly, the SR method penalized the total fruit yield of plants grafted with ‘Trooper Lite’ more often than those that were grafted with ‘Maxifort’. Our results suggest that plant growth and ultimately tomato fruit yield is affected negatively by using the SR grafting technique, particularly when less vigorous rootstock is used.