Global Assessment of Agricultural Productivity Losses from Soil Compaction and Water Erosion

The LTAR cropland common experiment in the Lower Mississippi River Basin

The Lower Mississippi River Basin-Long-Term Agroecosystem Research Site (LMRB-LTAR) encompasses six states from Missouri to the Gulf of Mexico and is coordinated by the USDA-ARS National Sedimentation Laboratory, Oxford, MS. The overarching goal of LTAR is to assess regionally diverse and geographically scalable farming practices for enhanced sustainability of agroecosystem goods and services under changing environment and resource-use conditions. The LMRB-LTAR overall goal is to assess sustainable row crop agricultural production systems that integrate regional environmental and socioeconomic needs. Primary row crops in the region include soybeans, corn, cotton, rice, and sugarcane with crop rotations influenced by commodity crop price and other factors. The field-scale common experiment (CE) includes four row crop farms (26-101 ha) established in 2021 and 2023. Three fields are managed with alternative practices, including reduced tillage, cover crops, and automated prescription irrigation, and three fields are managed with prevailing farming practices, consisting of conventional tillage, no cover crop, and nonprescription irrigation. Treatment effects on crop productivity, soil quality, water use efficiency, water quality, and carbon storage are assessed. Research from the LMRB CE will deliver outcomes linked to overarching LTAR network goals, including innovative agricultural systems, strengthened partnerships, data management technologies, and precision environmental tools.

Arbuscular mycorrhizal fungi alleviate erosional soil nitrogen loss by regulating nitrogen cycling genes and enzymes in experimental agro-ecosystems

Nutrient losses from agricultural ecosystems are increasingly threatening global environmental and human health. Although arbuscular mycorrhizal (AM) fungi have the potential to regulate soil nitrogen (N) loss by enhancing plant uptake and soil particle immobilization, the microbial mechanism behind such mycorrhizal effect is unknown. Herein, by conducting a simulated erosion experiment, we compared the effects of exogenous AM fungal inoculation (Funneliformis mosseae) on the gene abundances and enzyme activities of N-cycling processes, and associated such effect to N uptake and loss. The experiment was composed of combinations of two AM fungal treatments (control vs. AM fungal inoculation), two crops (maize vs. soybean) and two slopes of the plots (6° vs. 20°). The experimental plots subjected to natural rainfalls to simulate the erosion events. We showed that the effects of AM fungi were greater in the maize soils than in the soybean soils. In the maize soils, AM fungi increased the abundances of N-fixing (+81.1 %) and nitrifying genes (+200.7 %) and N cycling enzyme activity (+22.3 %). In the soybean soils, AM fungi increased the N-fixing gene abundance (+36.9 %) but decreased the abundance of nitrifying genes (-18.9 %). The abundance of N-fixing gene was positively correlated with N uptake but negatively correlated with N loss. Additionally, AM fungi enhanced the effects of mycorrhizal colonization and moisture but decreased the effects of nutrients on soil microbial metrics related to N-cycling processes. Therefore, AM fungal inoculation enhanced N uptake and reduced N loss by increasing N-fixing gene abundance, and that AM fungi should be preferably used for the low N environments or for the ecosystems highly limited by or competing for N.

Espial: Electrochemical Soil pH Sensor for In Situ Real-Time Monitoring

We present a first-of-its-kind electrochemical sensor that demonstrates direct real-time continuous soil pH measurement without any soil pre-treatment. The sensor functionality, performance, and in-soil dynamics have been reported. The sensor coating is a composite matrix of alizarin and Nafion applied by drop casting onto the working electrode. Electrochemical impedance spectroscopy (EIS) and squarewave voltammetry (SWV) studies were conducted to demonstrate the functionality of each method in accurately detecting soil pH. The studies were conducted on three different soil textures (clay, sandy loam, and loamy clay) to cover the range of the soil texture triangle. Squarewave voltammetry showed pH-dependent responses regardless of soil texture (while electrochemical impedance spectroscopy's pH detection range was limited and dependent on soil texture). The linear models showed a sensitivity range from -50 mV/pH up to -66 mV/pH with R2 > 0.97 for the various soil textures in the pH range 3-9. The validation of the sensor showed less than a 10% error rate between the measured pH and reference pH for multiple different soil textures including ones that were not used in the calibration of the sensor. A 7-day in situ soil study showed the capability of the sensor to measure soil pH in a temporally dynamic manner with an error rate of less than 10%. The test was conducted using acidic and alkaline soils with pH values of 5.05 and 8.36, respectively.

Root growth and physiological responses in wheat to topsoil and subsoil compaction with or without artificial vertical macropores

The process of soil compaction can cause various stresses on roots, ultimately limiting their growth and development within the soil. Understanding this phenomenon in real-world conditions can be challenging since the growth of roots is influenced by the soil environment. To investigate this issue, four experiments were conducted to examine the impact of topsoil (two in pots: with clay loam and sandy loam soils under two soil water regimes) and subsoil (in rhizobox: one with clay loam soil and the other with sandy loam soil, containing artificial vertical macropores) compaction on the relationship between edaphic factors and the physiological response of wheat roots. The topsoil compaction reduced root length, volume, and weight by 30-50% and the root diameter by ∼15% compared to the non-compact soil. The effect was reduced in the soil with higher clay content (clay loam), especially under the limited soil water condition. Plant physiological responses were adversely affected by compaction with a reduction in plant height. The transpiration rate was highly impacted (21-47% reduction) with the build-up of intercellular CO2 content in leaves (13-31%), especially with limited water applications. Root growth was severely restricted (>60%) in the compact subsoil layer, although the surface area and volume of roots increased in the overlying non-compact layer. Naturally occurring or artificial vertical macropores acted as escape channels, facilitating the roots to pass through the compact subsoil and grow abundantly in the loose soil below. However, plants in field conditions encounter a mix of loose and compact soil zones. By studying how roots respond to this soil heterogeneity, we can develop strategies to reduce the negative effects of soil compaction.

Farm vehicles approaching weights of sauropods exceed safe mechanical limits for soil functioning

Mechanization has greatly contributed to the success of modern agriculture, with vastly expanded food production capabilities achieved by the higher capacity of farm machinery. However, the increase in capacity has been accompanied by higher vehicle weights that increase risks of subsoil compaction. We show here that while surface contact stresses remained nearly constant over the course of modern mechanization, subsoil stresses have propagated into deeper soil layers and now exceed safe mechanical limits for soil ecological functioning. We developed a global map for delineating subsoil compaction susceptibility based on estimates of mechanization level, mean tractor size, soil texture, and climatic conditions. The alarming trend of chronic subsoil compaction risk over 20% of arable land, with potential loss of productivity, calls for a more stringent design of farm machinery that considers intrinsic subsoil mechanical limits. As the total weight of modern harvesters is now approaching that of the largest animals that walked Earth, the sauropods, a paradox emerges of potential prehistoric subsoil compaction. We hypothesize that unconstrained roaming of sauropods would have had similar adverse effects on land productivity as modern farm vehicles, suggesting that ecological strategies for reducing subsoil compaction, including fixed foraging trails, must have guided these prehistoric giants.

Soil Compaction Prevention, Amelioration and Alleviation Measures Are Effective in Mechanized and Smallholder Agriculture: A Meta-Analysis

Background: The compaction of subsoils in agriculture is a threat to soil functioning. Measures aimed at the prevention, amelioration, and/or impact alleviation of compacted subsoils have been studied for more than a century, but less in smallholder agriculture. Methods: A meta-analysis was conducted to quantitatively examine the effects of the prevention, amelioration, and impact alleviation measures in mechanized and small-holder agriculture countries, using studies published during 2000~2019/2020. Results: Mean effect sizes of crop yields were large for controlled traffic (+34%) and irrigation (+51%), modest for subsoiling, deep ploughing, and residue return (+10%), and negative for no-tillage (−6%). Mean effect sizes of soil bulk density were small (<10%), suggesting bulk density is not a sensitive ‘state’ indicator. Mean effect sizes of penetration resistance were relatively large, with large variations. Controlled traffic had a larger effect in small-holder farming than mechanized agriculture. Conclusion: We found no fundamental differences between mechanized and smallholder agriculture in the mean effect sizes of the prevention, amelioration, and impact alleviation measures. Measures that prevent soil compaction are commonly preferred, but amelioration and alleviation are often equally needed and effective, depending on site-specific conditions. A toolbox of soil compaction prevention, amelioration, and alleviation measures is needed, for both mechanized and smallholder agriculture.