Dryland cropping system intensification in the West-Central Great Plains: Impacts and barriers to adoption

View the project final report

• 2016 annual report

Commodities

• Agronomic: wheat

Practices

• Crop Production: continuous cropping, cropping systems, crop rotation, fallow, fertilizers, no-till, nutrient cycling, nutrient management
• Education and Training: Film
• Natural Resources/Environment: carbon sequestration, soil stabilization
• Production Systems: agroecosystems, dryland farming, holistic management
• Soil Management: nutrient mineralization, organic matter, soil microbiology, soil quality/health
• Sustainable Communities: new business opportunities, social networks

Cropping system intensification (reducing the frequency of unvegetated fallow years in crop rotations) has potential implications for the environment and economy of dryland agriculture as it impacts every aspect of the agroecosystem – from soil health, to nutrient management, to crop yields. The goals of this study were to quantify the effects of intensification on crop yields, fertilizer use, and soil properties related to carbon sequestration and nutrient cycling, and to determine how robust these effects are to variability in climatic, soil, and management factors. Additionally, despite the suggested benefits of dryland cropping system intensification, wheat-fallow remains a ubiquitous practice in the West-Central Great Plains, and we sought to understand the social dynamics underpinning decisions about whether and how much to intensify. We took soil and plant samples, and 6-year yield and fertilizer use histories, from dryland no-till fields from southeastern Colorado to northwestern Nebraska representing every level of cropping system intensity from wheat-fallow to continuous, 4-year rotations. Through in depth interviews with 25 farmers representing each level of cropping intensity, we uncovered the barriers to intensifying, and the strategies and motivations that have driven successful intensification.

We found that cropping system intensification was positively associated with soil organic carbon, aggregate stability, and fungal biomass, and these effects were robust amidst variability in environmental and management factors. Continuous rotations had 17% and 12% higher SOC concentrations than wheat-fallow in 0-10 cm and 0-20 cm depths, respectively. Aggregate stability in continuous rotations was about twice that in wheat-fallow rotations, and fungal biomass was three times greater in continuous rotations than wheat-fallow, but was not significantly different from mid-intensity rotations. Fungal biomass was positively correlated with aggregate stability. We also found that total and potentially mineralizable nitrogen (N) were 12% and 30% greater in continuous rotations relative to wheat-fallow, respectively, suggesting that internal N cycling was stimulated in continuous systems. Additionally, mid-intensity and continuous rotations had roughly 2 and 3 times more arbuscular mycorrhizal fungal (AMF) colonization than wheat-fallow, respectively, and AMF colonization was positively correlated with plant phosphorus (P) concentration. These results suggest that cropping intensity enhances internal cycling of N and phosphorus (P). Continuous dryland farmers also achieved 60% greater annualized crop production using a similar amount of fertilizer compared to wheat-fallow farmers. To explain the social dynamics underpinning decisions about intensification, we build on Carolan’s application of Bourdieusian social fields to agriculture, and find several overlapping fields within Carolan’s more general fields of sustainable and conventional agriculture, which are reflected in different degrees of intensification. In particular, we find that the emerging soil health movement, perceptions of risk and profitability, and crop insurance policy are drivers of the frequency of fallow on the landscape. We identify strategies for change, some of which would serve to reshape social fields, and others which leverage existing social positions and relationships, to enable farmers to overcome the barriers constraining cropping system intensification. We communicated these findings, and stories of farmers who have successfully intensified, to farmer and other audiences via blog posts, magazine articles, presentations at regional farming conferences and national scientific meetings, the drylandag.org website, and a short film.

Objective 1: Identify the social, ecological, political, and economic barriers to cropping intensification and the resources needed to eliminate or reduce the frequency of fallow in crop rotations.

Sub-objective 1: Examine the strategies farmers have employed to successfully intensify their cropping systems, and the obstacles faced by farmers with higher frequencies of fallow.

Sub-objective 2: Identify the factors that influence farmer decision-making at multiple scales.

Sub-objective 3: Identify the most effective educational, social, or political resources that could be mobilized to enable producers to intensify crop rotations.

Objective 2: Quantify cropping intensity effects on wheat and annualized grain yields, soil structure, and fungal biomass across management and climatic gradients.

Sub-objective 1: Compare winter wheat yields and annualized grain yields across farms with varying cropping intensity.

Sub-objective 2: Quantify cropping intensify effects on aggregate size and stability, intra-aggregate organic carbon, bulk density, and soil organic carbon.

Sub-objective 3: Assess the relationship between fungal biomass and soil aggregate stability.

Objective 3: Quantify the relationships between cropping intensity, nutrient cycling, fertilizer use, and crop yields.

Sub-objective 1: Quantify % AMF colonization of winter wheat roots and its effect on plant phosphorus (P) uptake.

Sub-objective 2: Quantify annualized grain production and fertilizer use across cropping system intensities.

Sub-objective 3: Quantify total and potentially mineralizable N across cropping system intensities.

Previously, we sought to measure leaf water potential as an indicator of drought stress in wheat. After one sampling at the most drought-prone site, we concluded there was no measurable pre-dawn or midday drought stress. We have since changed this objective (Sub-objective 1 of Objective 3) to examine the effect of % AMF colonization of winter wheat roots on plant P concentration.