Recent research by Chatterjee et al. (2015) and Aher et al. (2016) have shown that significant levels of crop residues can accumulate in crop rotations in which high residue crops such as wheat or corn are frequent component crops. This residue accumulation is partly due to the relatively cool climate in the northern Great Plains of the U.S. High residue producing crops often have high N requirements. N fertilizer is a major input in the cost of crop production but little information is available in the literature about the rate of N mineralization and the N contribution of residue decomposition to the N requirements of subsequent grain crops in longterm no-till culture. We have just completed laboratory research that shows that most crop residues after harvest have wide C:N ratios which encourage N immobilization rather than N mineralization. We have also noted that adding a high N-mineralizing cover crop such as forage radish may negate the immobilization through supplementing microbial N needs during the rapid growth phase of crop development. Since this previous work was done under optimum laboratory temperature and moisture conditions, we need to validate our findings under field conditions. Knowledge of the mechanisms of N cycling from post-harvest crop residues in combination with effects of cover crops in long-term no-till culture will information growers on improved decisions about the most efficient use of their fertilizer N applications.

The objective of this research is to:
(a) evaluate and validate our laboratory research on N-mineralization/immobilization processes in a field environment; and
(b) determine how varying temperature and moisture conditions in a field environment affect crop residue decomposition and N mineralization under a no-till culture.

This study is currently providing information on soil moisture and temperature changes during the growing season. Soil sampling during the season will provide information on soil plant available N related to the residue(s) accumulating on the soil surface. This information will be presented at fanner/grower workshops and incorporated in research and extension publications providing farmers with information to make sound fertilizer management decisions.

Updated March 25, 2022:
2021 Mid-Year Summary of Results
Name(s): Larry Cihacek and Rashad Alghamdi, NDSU SNRS – Soil Science, Fargo, ND 58108
Title: Field Validation if Mineral N Cycling from Mixed Crop Residues in Long-term No-till Systems
Objectives of the Research:
The objective of this research is to:
1. Evaluate and validate our laboratory research on N-mineralization/immobilization
processes in a field environment;
2. Determine how varying temperature and moisture conditions in a field environment
affect crop residue decomposition under a no-till culture; and,
3. Evaluate whether a cover crop (e.g. radish) can help mitigate N immobilization under
field conditions.

Completed Work:
A series of microplots were established on a Fargo soil on the NDSU campus in May of 2021. Each microplot was 15 inches in diameter and was surrounded by a ring constructed with landscape edging. A time-domain reflectrometry (TDR) probe was installed at a depth of 5 cm near the center of the microplot. The microplots were arranged in “nests” of 5 plots in order to accommodate a data logger to collect continuous temperature and moisture data from the 5 plots (Figure 2). Crop residues at a calculated rate of 6.25 T/A were applied to all plots except the bare soil controls. The residue was either left on the surface (no-till) or incorporated with the soil (conventional tillage) in three replications. A set of microplots also received the same treatments but with the equivalent of 30 lbs. N/A as a urea solution to evaluate the potential priming effect of N fertilizer. The residue treatments represented the same treatments used in previous laboratory incubation studies. Soil N samples were collected at the beginning of the study, in July and in October (end of season). Theses samples are still being processed through the laboratory and data is not available at the writing of this report.
Preliminary Results:
The summer of 2021 at Fargo was very dry with low rainfall and above average temperatures through early August. Consequently, very little residue decomposition appeared to have occurred during the growing season. Thus, a parallel study was established in the laboratory to complement the field study utilizing identical crop materials and rates of residue to supplement the data obtained from the microplot study. The incubations are currently ongoing and N mineralization/immobilization data is being collected and the data is being summarized at the writing of this report.
Figure 1 illustrates the temperature and moisture data collected from the soybean residue plots where the residue was applied on the soil surface or mixed into the surface 5-10 cm of the soil with or without the equivalent of 30 lbs N/A N fertilizer from May through July. This kind of data has also been collected from July through October and is still undergoing analysis. Even though the daily air temperatures were warm during this period, the daily soil temperatures still averaged below 25°C (77°F). Rainfall cooled the soil while soil drying caused increasing temperatures. The diurnal (day-night) changes along with soil cooling due to rainfall and soil warming due to soil drying can greatly impact microbial activity resulting in residue decomposition. This along with variable soil wetting and drying (soil moisture) will slow microbial action upon the residue.
Work to be Completed:
We would expect that N mineralization rates would be lower under actual field conditions than under controlled conditions in the laboratory. We envision to continue this work for two more seasons in order to establish a clearer picture of actual soil conditions that contribute to N mineralization or immobilization from decomposing crop residues. The residue levels being used in this study appear to be realistic levels found post-harvest in many North Dakota Farmers fields. We plan to include PLFA and qPCR analyses on selected treatments during the next year. These are commonly used techniques often used for higher level evaluation of soil health based on soil management.

View uploaded report

Updated June 30, 2022:

View uploaded report

Updated December 14, 2022:

View uploaded report

View uploaded report 2

Updated December 15, 2022:

View uploaded report

View uploaded report 2

The results of this research will provide information to farmers, consultants and Extension personnel so they can modify or adapt soil test recommendation and fertilizer practices in long-term no-till (>5 years) to economically account for heavy crop residues in corn-soybean or wheat-soybean production systems. This knowledge will also provide information to better understand soil health in long-term no-till production systems.