There is no universally accepted definition, but in general organic farming is a production system, which avoids or largely excludes the use of synthetically compounded fertilizers, pesticides, growth regulators, and livestock feed additives. Organic systems emphasize use of renewable resources and conservation of soil and water, enhance environmental quality for future generations. The breadth and quality of soil organic carbon in agroecosystems affects soil’s physical, chemical, and biological properties and therefore influences soil productivity and the sustainability of certain production systems. Soil quality is an integral aspect of soil sustainability and can be used to determine sustainability on a soil to soil level. These two ideas have been linked as “inseparable” and soil quality is considered a “key indicator” of ecosystem sustainability. Recently, with growing concerns over soil degradation and the need for more sustainable soil management practices, there has been a marked emphasis on the value of soil and its properties pertaining to specific ecological and agricultural functions.
The objectives of this study were to identify land use systems and soil/vegetation management practices that lead to an enhanced SOC pool, principally with regards to compost, cover crops, various forms of organic manure, and crop residue. Specific objectives are: to comparatively assess soil quality changes in conventional fanning vis-a-vis organic farming practices, quantify the effects of organic farming practices on crop yield, and establish relation between soil quality indicators and crop yield.
This study was broken into two parts, a 6 farm survey and an experimental plot with 6 replications. In this two-year experiment, 3 pairs of farms were sampled for biometric parameters, crop yield and aboveground biomass yield. In each pair there was a certified organic farm and a conventional farm with matching soil types to eliminate yield differences due to exogenous soil variations. The soils sampled were Blount, Bennington, and Chili silt loams, all planted to corn (Zea mays). On each farm, 3x3m adjacent plots were chosen for core sampling at 0-30cm depth. Overall, the conventionally managed farms did have higher yields across years with an average of 5.3 Mg ha-1, but in 2004 the Chili silt loam organic farm surpassed two of the conventional farms in grain production with 6.4 Mg ha-1 compared to 4.6 and 4.4 Mg ha-1. The Chili silt loam farm has been under organic management for 20 years, the longest period of time compared to the other organic farms. This agrees with other studies that have found organic systems under long-term management often have similar yields to conventionally managed farms.
In this experiment, the 3 pairs of farms were also sampled for a range of soil quality indicators including: pH, mean weight diameter (MWD), water stable aggregation (WSA), bulk density, available water capacity (AWC), cation exchange capacity (CEC), and soil organic carbon and nitrogen pool. After analysis, the values for each parameter were assigned a soil quality index rating to compare overall soil quality of each management system. There are many different indices that can be used to measure soil quality but the one implemented here did not reveal a trend according to management system. The Blount silt loam organic farm did have the best soil quality but the two other organic farms had the worst ratings. These findings do not correlate with past studies, which found organic management increased overall soil quality when compared to conventional practices.
In second part of the two-year experiment, a complete random block design was used to test six treatments on various soil quality indicators. These treatments included cover crop, dairy manure, tannin bark compost, fallow, control and Triple 19 fertilizer. The treatments were used to represent common conventional and organic management practices. The synthetic fertilizer and manure yielded the highest amount of corn among the six treatments. According to the soil quality index implemented, organic and conventional farming practices had a similar soil quality index. The synthetic fertilizer and manure treatments also received the highest soil quality ratings while the compost had the lowest yield and worst soil quality rating. These findings expressed a correlation between crop yield and soil quality for this study. This information must be coupled with other long-term studies to more accurately explore the connection between organic agricultural practices and soil quality.