Soil Thermal Properties of Peat Based Media Amended with Organic Fertilizers and Grown to Three Vegetables.

We investigated the effects of growing media amendment with organic fertilizers and vegetable species on soil temperature (T), thermal conductivity (K), thermal resistivity (R), thermal diffusivity (D) and volumetric heat capacity (C). The study was conducted from June to September 2011 in a greenhouse at Lincoln University. One hundred and twenty pots were filled with Fafard organic soil and amended  with three organic fertilizers: Cottonseed meal (6-2-1), Dried Blood (12-0-0), Garden Food (4-3-2) and NPK(13-13-13). A control treatment made of non-amended Fafard organic soil was also included in the study. The experimental design was a completely randomized block with 5 fertilizers treatments and 3 vegetables replicated 8 times. Soil T, K, R, D, C and vegetables growth parameters were monitored throughout the four months of this study. At the end of each month, plants were harvested for measurements of plant height (PHT), leaf area (LA), plant  dry weight (PDW) and root dry weight (RDW). Results showed that soil thermal properties were: 29.81^oC, 0.34 W/m^oK, 3.56 m^oK/W^-1, 0.16 mm/s and 2.09 MJ/m^3oK for T, K, R, D, C respectively at the beginning and slightly increased (T, K, C) or  decreased (R, D) after four months of study. Fertilizers did not significantly affect soil thermal properties. However,  vegetables significantly affected  R (p=0.002) during the second month, but also K (p=0.022), R (p = 0.0001) and C (p=0.004) during the last month of this experiment. After four months of growth, K (p= 0.0005, r =-0.31); R (p=0.0009, r =0.30) and C(p= 0.0173, r =-0.22) significantly correlated with PDW. K (p=0.0060), D (p=0.0107), R(p=0.0492) also significantly correlated with RDW. Soil K, R and C correlated with vegetables growth parameters when T could not. Therefore, K, R and C offer a promise for assessing the relationships between heat flow and plant growth in growing media.