Date of Award

12-2021

Degree Name

MS in Agriculture - Plant Protection Science

Department/Program

Horticulture and Crop Science

College

College of Agriculture, Food, and Environmental Sciences

Advisor

Charlotte Decock

Advisor Department

Natural Resources Management

Advisor College

College of Agriculture, Food, and Environmental Sciences

Abstract

Effects of nitrogen management and cultivar on strawberry production under disease pressure

Kamille Garcia-Brucher

California strawberry growers face increasing regulatory pressures to manage nitrogen (N) applications in their production system. Standard practice in the California strawberry industry is to apply a synthetic pre-plant controlled release fertilizer (CRF) to ensure the crop has sufficient N during winter establishment. Some research from the UC Cooperative Extension suggests this practice is not efficient at delivering N to the crop since most of the N is released from CRF before strawberry crop N uptake is significant. Another concern for California strawberry growers is loss of their crop to a myriad of soilborne pathogens. Compost is commonly applied as a soil amendment in California strawberry fields as it offers both agronomic and environmental benefits including the potential for disease suppression. In light of legislation restricting N in some California cropping systems, Ag Order 4.0, and incentives programs established to promote soil conservation practices, compost may be a viable substitute for synthetic pre-plant CRF N. In this study, we investigated the effects of pre-plant fertilizer and strawberry cultivar on fruit yield, disease incidence, soil and plant N dynamics and soil carbon (C) at the Cal Poly Strawberry Center, San Luis Obispo, CA in a field infested with Macrophomina phaseolina. Pre-plant fertilizer treatments included 100 lb N/ac Cal Poly certified organic compost, 100 lb N/ac synthetic CRF and a control treatment (0 lb N/ac). Strawberry cultivars included three UC varieties, ‘Monterey,’ ‘Albion,’ and ‘San Andreas,’ and one Driscoll’s proprietary cultivar. Fruit yield and plant mortality data were collected throughout the growing season. Soil C was measured from soil samples collected in the root zone (6 in) while soil nitrate was measured from pore water samples collected in and below the root zone (6 and 12 in, respectively). Strawberry crop N uptake was determined using destructive plant samples while fruit N concentration was determined from subsamples of harvested fruit taken in April, May, June, and July each year. Although compost application did not significantly affect C sequestration and did not reduce disease incidence, there was no significant difference in total yield between compost and CRF treatments suggesting that compost can substitute for synthetic CRF without negatively affecting yield. There was significantly less plant mortality in control treatments compared with compost and CRF treatments suggesting excessive pre-plant N impacts disease incidence by M. phaseolina but more research is needed to better understand the mechanisms of infection by this soilborne pathogen. Total yield in this experiment was lower compared with statewide averages and crop N concentration was lower compared with the literature which is likely a result of disease pressure. Fruit N concentrations for the cultivars in this study were lower than the conversion coefficient defined by the Ag Order which means growers are removing less N through harvest allowing them more room in their N budget. Based on our results, compost may be substituted for synthetic CRF without negatively affecting yield and perhaps even make desirable soil improvements in this production system. And in fields with significant levels of M. phaseolina in the soil, N applications should be considered as it was seen to impact disease incidence.

Keywords: compost, controlled release fertilizer, M. phaseolina, nitrogen uptake, Ag Order 4.0

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