Evaluation of the effectiveness of Colorado State University's compost for lettuce production

Abstract

The impact of Colorado State University (CSU) compost application at high and low rate (36.48, HC, and 9.52, LC, kg/acre respectively) on red leaf lettuce (Lactuca sativa) production in a high hoop house was evaluated during spring of 2014. Measurements used to evaluate production was plant height, leaf number, fresh weight, leaf area, dry weight and relative photosynthesis. Leaf nutrient content of the red leaf lettuce was also compared among treatments. The experiment was conducted in a high tunnel at the Horticulture Field Research Center (HORT Farm) at Colorado State University in Fort Collins. CSU compost treatments at HC and at a LC were compared to Alaska fish fertilizer 5-1-1 (41.2ml/7.6 liters once a week) and no fertilizer as a control. The experiment was set up in a randomized complete block design with four treatments and three replications in the high tunnel (15.24 ×6.096 m) for a total of 12 treatment replication combinations. Samples were taken at 3 times (after 25, 35 and 45 days after transplanting, DAT). JMP software program was performed and statistical significance was determined using analysis of variance followed by Student's t test for mean comparison. CSU compost analysis showed that the organic matter and C/N ratio (60.1%, 22.8 respectively) were high indicating that nitrogen may have been immobilized in the high carbon. Also, the salt level was high (3.5 mmhos/cm) which may have impacted production of the lettuce. The total nitrogen in the compost was at a moderate level (0.53%) which should have supplied sufficient nitrogen to the lettuce. Nitrate-N was high (92.7 ppm) while ammonium-N was low (19 ppm) indicating that this compost had matured. Results under low concentration of CSU's compost (LC, 9.52kg/acre) showed a significant increase in several perimeters as follow; leaf number of 18.06 after 45 days, a fresh weight of (269.86 g) after 45 days, a leaf area of (232.5 cm²) after 25 days, and total dry weight of (12.5g) after 45 days when compared to the other treatments. The LC (9.52kg/acre) application had significantly greater total N at 4.28% at 25 days after transplanting. Also, LC, fish and control treatments contained similar levels of P (6.98, 6.87 and 6.64 mg/g respectively) after 45 days from transplanting but differ when compared to 25 and 35 days. There were no significant differences in potassium (K) levels among compost treatments and the control treatment of leaves of red leaf lettuce. On the other hand, at the LC and HC concentrations of CSU's compost there was a significant increase in K concentration from 25 and 45 DTA. The lettuce grown under HC (36.48 Kg/acre) had a significant increase in the Sodium (Na) level at 25 and 35 DTA (6.45 and 4.45 mg/g) when compared to the control (3.63 and 3.24 mg/g) respectively. The HC (36.48Kg/acre) had a significant reduction in Mg, Fe, and Al concentration at 35 days DTA when compared to the control (C) (3.14, 0.05, 0.62 mg/g respectively). There were a few differences in the minor elements when treatments were compared as follows: calcium was significantly lower in the HC (8.81mg/g) after 35 days when compared to control treatment; there was a significant increase in zinc (0.05 mg/g) after 35 days of transplanting when compared to the control as well. There were no significant differences among the CSU compost treatments and control treatments for Nitrate concentration and manganese. Colorado State University compost may be used as a nutrient source for red leaf lettuce production. However, high rates of application of the compost may be a problem as it contains high salt levels. Leaching of the salts is recommend when high levels of the compost is used.