2015/07/01 by S. Castro Bustamante, T.K. Hartz · 2 citations
Agricultural and Biological Sciences · #Plant nutrient uptake and metabolism #Soil Carbon and Nitrogen Dynamics #Irrigation Practices and Water Management
paper · pdf · doi:10.21273/hortsci.50.7.1055
Organic processing tomato ( Solanum lycopersicum L.) production is a significant industry in California, yet little nitrogen (N) fertility research is available to guide N management. A total of 37 certified organic processing tomato fields in the Sacramento Valley of California were monitored during the 2012 and 2013 production seasons, with two objectives: 1) to document current N management practices and 2) to investigate the utility of early-season soil and plant N monitoring techniques in predicting seasonal crop N sufficiency. Between ≈3 and 11 weeks after transplanting (WAT) soil mineral N (SMN), leaf N and petiole NO 3 -N were determined every other week. In 22 fields, whole plant N concentration at ≈11 WAT was determined as a measure of crop N sufficiency. Growers were surveyed regarding N management practices used and fruit yields achieved. Net N mineralization (N min ) was measured for 20 fields soils by aerobic laboratory incubation. Carbon mineralization (C min ) in 24 hours following rewetting of air-dried soil and water extractable organic nitrogen (WEON) and carbon (WEOC) were also determined and evaluated as predictors of N min . Nitrogen management was primarily based on the application of manure or manure compost in the fall. Organic fertilizers were applied mainly in spring (pre- and post-transplanting). SMN in the top 60 cm at 3 WAT ranged from 6 to 32 mg·kg −1 . About 30% of fields were N deficient by 11 WAT. Sensitivity analysis showed that SMN (whether measured from 0 to 30 or 0 to 60 cm) and leaf N at 5 WAT correctly predicted late-season plant N status in >60% of the fields. N min in 28 days ranged from 8 to 31 mg·kg −1 , representing an average of 2% of total soil N. Correlation between N min and C min was weak ( r = 0.44, P = 0.051) while stronger correlations were observed between N min and WEOC, WEON and total soil N ( r = 0.63, 0.61 and 0.51, respectively, all P < 0.03). A multiple linear regression model that used 3 WAT SMN (0–30 cm) and WEON as independent variables improved N min prediction (adj. R 2 = 0.67). Significant fruit yield increase with sidedress N application of feather meal at 5–6 WAT was observed in 2 of 4 field trials, demonstrating the ability to remedy a soil N limitation identified by early-season N monitoring.