Organic and Conventional Agriculture: Learning from Each Other to Promote Soil Health and Economic Viability in West Texas

Figures: ResearchResults_Figures_202020212022 

2019

Analysis of soil samples collected in the spring of 2019 are still being analyzed. Current data is limited to β-glucosidase and mineralizable C. Results indicate that microbial activity is similar across systems which is what would be expected since systems had not been implemented. However, there were differences determined among soil depths with the greatest microbial activity in the 0-4” sample depth. These results are in line with expectations, as microbial activity tends to decrease with soil depth. These samples provide baseline data against which to compare future results. Soil moisture and greenhouse gas flux measurements will be collected in 2020 following cover crop termination; data will be included in next report.

Since cover crop treatments had yet to be implemented, the yield was averaged across treatments for the organic and conventional systems. At Lubbock, the mean yield for organic and conventional cotton was 344 lb/ac and 492 lb/ac, respectively. At Vernon, the mean yield for the organic cotton was 607 lb/ac vs. 946 lb/ac for the conventional cotton. Delayed maturity and lack of an applicable harvest aid in organic cotton (along with genetics) were potential reasons for reduced yields.

2020

In 2020, soil samples were collected at both small plot research locations (Lubbock and Vernon, TX) and at on-farm sites following cover crop termination. Prior to cover crop termination, biomass samples were collected from cover crop plots to determine herbage mass production and C and N content. Those samples have been analyzed for enzyme activity, PLFA, and C mineralization. We are still in the process of completing organic C and total N determination. Greenhouse gas flux measurements and soil moisture content were collected during the 2020 peanut growing season. Peanuts were harvested and yields were determined.

From small plot research trials, we determined generally greater CO₂-C fluxes from the conventional treatments compared to the organic systems at the Lubbock location (Figure 3); however, there was no clear separation between organic and conventional production at the Vernon site (Figure 4). Differences in CO₂ fluxes between the two locations was unexpected. Consistently, no cover crop (winter fallow) resulted in the least amount of CO₂-C lost from the soil surface (Figures 3 and 4), which was not surprising due to additional root respiration and added organic material from the cover crop which stimulates microbial activity and greater CO₂ production. The next step will be to calculate net CO₂-C losses by subtracting the amount of C sequestered by the cover crop from the gross emissions. Limited C mineralization differences amongst systems were not determined which was unexpected due to the drastic differences in management practices (Figures 5 and 6).  Enzyme activity determination and analysis are being completed; preliminary data are presented in Figure 7.

Peanut yield was averaged by the system (conventional w/ cover, conventional/winter fallow, and organic w/ cover) due to the lack of differences caused by the cover crop treatments (species and seeding rates). There were no differences at either location; however, there was a general decrease in peanut yield from organic to conventional (with and without a cover) practices at the Vernon location (Figure 8).

The data collected from on-farm locations indicate inherent soil properties and management practices are influencing biological components such as soil organic C (SOC). For example, when comparing SOC between organic and conventional management, the results are inconsistent (Figure 12). The same is true with potassium permanganate oxidizable carbon (Figure 13). However, the management system at the Brown farm site affected enzyme activities (Figure 14). Activities for β-glucosidase, β-glucosaminidase, arylsulfatase, and alkaline phosphatase were all significantly greater under conventional management, compared to organic at 0-4”. The only significant difference at 4-8” was β-glucosaminidase which was greater in conventional. On-farm, results are in stark contrast to those from the small plot studies at the Lubbock and Vernon research sites, which showed no differences and generally increased enzyme activity under organic management, respectively. This difference is likely due to weed control methods between on-farm and small plot research sites in the organic systems. Hand weeding was the primary weed control method in the organic small plot study, while farmers primarily used tillage in their organic systems. Hand weeding disturbs the soil much less than tillage and is likely the most significant contributing factor to organic management having similar or higher enzyme activity compared to conventional in the small plot study, but not on farms.

2021

2021 was the last transitional year for the organic treatments and the first year of cotton following cover crop treatments. In Lubbock, there was minimal difference in biomass production among cover crop treatments, although rye at 30 lb/acre and the mixture of rye at 25/vetch at 3/radish at 2 lb/acre, were significantly higher than all other treatments, and radish only treatments were significantly lower than all other treatments (Figure 15). In general, at both locations, the highest seeding rate of cover crop treatments under organic management was not different from the middle seeding rate. This means recommendations to producers regarding cover crop seeding rates can be made for the lower seeding rate in order to reduce costs. Conventional yields were significantly greater than organic at both Lubbock and Vernon at 858 and 905 lb cotton lint per acre, respectively (Figures 16 and 17). Organic yields were 395 and 457 lb cotton lint per acre, respectively, at Lubbock and Vernon.

2022

The first year of organic certification was 2022 and the second peanut crop of the 4-year study. At Lubbock, cover crop biomass production was similar with all rye cover treatments in both conventional and organic systems (Figure 18).  Radish only produced less cover crop biomass (<250 lbs/A) in both systems.  At Vernon, cover crop mixtures containing rye produced greater biomass than treatments without rye or rye alone (Figure 19). 

Weed population counts were conducted in each plot on June 27 and July 29 during peak weed emergence.  Weed counts collected on June 27 indicated lower weed populations in both fallow and cover crop mixtures in conventional production compared to organic plots (Figure 20).  The differences were even more dramatic at the July 29 rating with weed counts averaging 70,000 weeds/A (Palmer amaranth and purslane) compared to less than 1,000/A in both conventional fallow and cover crop systems (Figure 21). Biomass production of organic treatments with cover crops did not affect weed counts. These results indicate that organic peanuts without the ability to cultivate throughout the growing season makes weed control difficult and expensive if depending on hand hoeing as the primary means of control.

Soil samples were taken monthly following peanut planting (June). Samples will be analyzed for soil health and nutrient parameters, including mineralizable carbon, enzyme activities, and phospholipid fatty acids (PLFAs). Mineralizable carbon and enzyme activities are in the process of being analyzed in-house, while PLFA samples will be shipped to a specialized laboratory before the end of the year. Mineralizable carbon has been analyzed from June in Vernon, and results follow trends from previous years, in that organic management significantly increases mineralizable carbon over conventional and fallow (Figure 22). Mineralizable carbon was less affected amongst cover treatments at the 0-10 cm depth at Vernon (Figure 23).

Economic analysis over three years of transition reveals interesting results. Net gain per acre was significantly reduced at both sites in each of the three transitional years under organic management compared to conventional (Figure 24). This was primarily caused by increased weed control costs in organic systems increasing the total production cost of the system (Figure 25). Organic systems required 4-8 hand weeding events per year at an average cost of 100-$150 per acre, accounting for 84% of total costs. Conventional weed control only accounts for 41% of per-acre costs. An important note is that most organic producers in the Texas Plains regions perform tillage events to control weeds, rather than hand-weeding events. Tillage has been reported to greatly reduce soil health indicators compared to no-till systems regardless of conventional or organic management so, the economic data from this study should be interpreted as the additional costs associated with organic management practices which increase soil health indicators. Based on this data, it may be difficult to recommend a switch to organic management, with the purpose of increasing soil health, to a farmer in the Texas Plains due to the lack of economic viability.

Overall, the results from this study do not indicate improved environmental or economic sustainability of organic cotton and peanut production systems. The slightly enhanced soil health dynamics reported in small plot research with organic production were not observed on farmer fields. Implementing cover crops and reduced tillage which are the main drivers of improved soil health are not easily accomplished in organic production as compared to conventional systems.