Cover Crops for Improving Nitrogen Use Efficiency in a Semiarid Irrigated Forage Rotation

Progress report for GW21-226

Project Type: Graduate Student
Funds awarded in 2021: $20,612.00
Projected End Date: 04/30/2023
Host Institution Award ID: G216-22-W8615
Grant Recipient: New Mexico State University
Region: Western
State: New Mexico
Graduate Student:
Major Professor:
Dr. Rajan Ghimire
New Mexico State University
Major Professor:
Pramod Acharya
New Mexico State University
Vance Dewbre
Kiva Farms, LLC
Expand All

Project Information


Livestock production contributes to >40% of the agricultural economy in New Mexico. High yield and quality of forage provide the foundation for the success of the livestock-based economy. However, sustaining forage-based agriculture in the southwestern region is challenged by low water and nutrient use efficiency. Because of the high demand for feed and forage, farmers often over-apply N fertilizer to increase forage productivity. Forage crops require a large amount of nutrients, specifically nitrogen (N). However, high N application rates in irrigated forage production systems can lead to N loss through leaching and runoff. Cover cropping can increase N-use efficiency by improving N recycling in the cover crop-integrated forage production system. Enhanced knowledge of N-movement in the soil profile under fallow and cover crops will help optimize N management and minimize the environmental risk associated with N leaching. Synchronizing N release from cover crop residues can reduce the N-requirement of forage crops and increase farm profitability.

We propose to evaluate the effects of diverse cover crop mixes on crop N-use efficiency in an irrigated forage corn-sorghum rotation system. Soil water samples from soil profiles will be monitored once a month for inorganic N content. Cover crops and forage biomass and their quality parameters will also be estimated. Research findings will be shared with growers through farmer’s field day, extension workshop, regional conference, and extension article publication. The project will address the knowledge gap regarding the cover cropping benefits in the forage production system.

Project Objectives:

Research Objectives

  1. Estimate the soil inorganic N content using deep-profile water samples in a cover crop-integrated forage production system.
  2. Determine crop yield and N-use efficiency of forage crops.

Education/outreach Objectives

  1. Disseminate the project results to the local growers and the general audience (researchers, educators, students, and policymakers). 
Activities 2021 2022 2023
Aug Sept Oct Nov Dec Jan Feb Mar Apr May June July Aug Sept Oct Nov Dec Jan Feb Mar Apr
Seasonal monitoring of crops
Cover crops plantation X X                                      
Cover crops termination                 X                        
Forage (corn & sorghum) plantation                   X                      
Forage (corn & sorghum) harvest                           X              
Crop measure
Cover crop biomass                 X                        
Cover crop quality                  X X X                    
Forage biomass                           X              
Forage quality                           X X            
Sampling   X             X         X              
Monthly monitoring of soil inorganic nitrogen from water samples and soil profile moisture content   X X X X X X X X X X X X X              
Outreach activities
Farmer's field day and visit                 X       X                
Project evaluation     X   X       X   X   X     X          
Extension and journal article                                   X X X X
Social media coverage On special project events
Talks on different forums, attend and present at conferences Based on the organizer's schedule
Mid-term and final reporting             X                       X X X


Materials and methods:

Research objective

The main objective of this research is to evaluate the efficacy of cover crops in improving the N-use efficiency of forage crops in an irrigated semi-arid cropping system.

Research Objective 1: Estimate the soil inorganic N content using deep-profile water samples in a cover crop-integrated forage production system. Integrating cover crops in forage production systems is expected to capture soil inorganic N and benefit the cropping system by using N mineralized from cover crop residues at the time of subsequent crop need.

Materials and Methods for objective 1

The research was initiated in September 2021 in an ongoing project established in fall 2018 at NMSU-Agricultural Science Center (ASC), Clovis, NM (34°36’59” N, 103°13’06” W, and elevation 1368 m above mean sea level). The study area has an annual average maximum and minimum temperature of 22.2°C and 6.1°C, respectively, and precipitation of 452 mm. The study site has an Olton clay loam (fine, mixed, superactive, thermic Aridic Paleustolls) soil based on USDA classification.

The study was laid out in a randomized complete block design with four cover crop treatments and four replications. The major cash crop included forage corn (Zea mays L.) and sorghum (Sorghum bicolor L. Moench) in a rotation. Each plot has a 9.1 m (30 ft.) x 12.2 m (40 ft.) size. The treatments included:

  1. Fallow, no cover crops (NCC)
  2. Mixtures of grasses, brassicas, and legumes (GBL)
  3. Mixtures of grasses and brassicas (GB)
  4. Mixtures of grasses and legumes (GL)

where grasses included annual ryegrass (Lolium multiflorum Lam.) and winter triticale (Triticale hexaploid Lart.), brassicas included turnip (Brassica rapa subsp. rapa) and daikon radish (Raphanus sativus var. Longipinnatus), and legumes included pea (Pisum sativum subsp. arvense L.) and berseem clover (Trifolium alexandrinum L.).

The winter cover crops were planted on September 23, 2021, and terminated on April 28, 2022, using a mixture of chemical herbicides. Forage corn and sorghum were planted on May 17, 2022.

After cover crop planting in 2021, soil solution access tubes (SSAT) (Irrometer Company, Inc., Riverside, CA) were installed on September 29, 2021. In the cover crop - forage sorghum rotation, three different depths of SSAT, i.e., at 18, 24, and 36 inches, and in the cover crop - forage corn rotation, two different depths of SSAT, i.e., 18 and 24 inches, were installed.

On May 10, 2022, we collected soil samples from each plot at 0–80 cm depth using a tractor-mounted hydraulic probe (Giddings Machine Company Inc., Windsor, CO). The collected samples were divided into 0–20, 20–40, 40–60, and 60–80 cm depths. The subsample of about 5-g was extracted in 25 ml of 1-M KCl solution and analyzed for inorganic N (NO3 + NH4) using an automated Timberline Ammonia Analyzer (Timberline Instruments, Boulder, CO, USA).

Project modifications note:

Due to the low precipitation during the cropping season, we could not collect the water samples from the SSAT as proposed. Thus, we collected soil samples from 0–80 cm depth and analyzed them for inorganic N at the cover crop termination. The same protocol will be followed at the time of cash crop harvest so that we will have comparable data at least for the cash crop phase of crop rotation.

Installing soil solution access tubes with Dr. Paye (top left); soil solution access tube after installation (top right); applying a vacuum to extract water samples inside the soil solution access tubes (bottom left); and soil sampling from deep profile in May 2022 (bottom right)
Figure. 1. Installing soil solution access tubes with Dr. Paye (top left); soil solution access tube after installation (top right); applying a vacuum to extract water samples inside the soil solution access tubes (bottom left); and soil sampling from deep profile in May 2022 (bottom right)

Research objective 2: Determine crop yield and N-use efficiency of forage crops. Cover cropping is expected to improve the crop yield and quality supported by enhanced fertility and efficient use of nutrients.

Materials and Methods for objective 2

Cover crop biomass samples were collected by hand-clipping the aboveground biomass from four randomly thrown 0.25 m2 quadrants in each cover crop plot. The collected cover crop biomass was oven-dried at 65ºC for 72 hrs. to estimate the dry weight. The cover crop subsamples were ground in a ball mill (Thomas-Wiley laboratory mill, model 4, Arthur H. Thomas Company, Swedesboro, NJ) and sent to Ward Laboratories Inc., Kearney, NE, for forage quality analysis using near-infrared reflectance spectroscopy.

Cover crops in their early growth phase in October 2021 (left) and cover crop biomass sampling before their termination in April 2022 (right)
Figure 2. Cover crops in their early growth phase in October 2021 (left) and cover crop biomass sampling before their termination in April 2022 (right)
Research results and discussion:

In the cover crop-forage sorghum rotation, the average cover crop aboveground biomass yield was 0.75–1.33 Mg ha-1, while it was between 1.39–1.43 Mg ha-1 in the cover crop-forage corn rotation. With this, the aboveground cover crop biomass would supply 20–38 and 35–37 kg N ha-1 for subsequent sorghum and corn, respectively. However, in a 0–80 cm soil profile, cover crops at the termination stage reduced 78–89% of soil inorganic N compared to NCC (NCC, 123–225 kg N ha-1 vs. cover crops, 14–49 kg N ha-1). Preliminary results show that cover crops can capture N and prevent it from gaseous or leaching loss. The captured N in the cover crop biomass can be recycled back into the system and potentially utilized by the subsequent cash crop. We are continuing N monitoring this summer and fall as well. All the data will be analyzed this fall to see specific trends in N cycling with diverse cover cropping practices.

Participation Summary
1 Farmer participating in research

Educational & Outreach Activities

1 Consultations
1 Webinars / talks / presentations
1 Workshop field days

Participation Summary:

63 Farmers
63 Ag professionals participated
Education/outreach description:

We introduced the research project and discussed the project objectives and activities with the farmers/producers and agricultural professionals present on the field day in 2021. The event was organized by New Mexico State University Agricultural Science Center at Clovis, NM, on August 4, 2021. Also, we presented some part of the research data at the Western Society of Crop Science Annual Meeting (June 21–22) in Fort Collins, CO (link for presentation). Agricultural professionals, researchers, and students from western regions of the USA were present at the meeting.

Project Outcomes

Did this project contribute to a larger project?:
Project outcomes:

The study is still in progress; early results indicate that cover crops can capture a significant amount of the residual N from the deep soil profile. After the cash crop harvest, we will estimate the N budget in cover-crop integrated systems and determine the N-use efficiency.

Knowledge Gained:

Depending on soil types, crops, and management conditions, agricultural sustainability could mean multiple things. Water is probably the predominant driver of sustainable agriculture in the arid and semi-arid southwest. We learned soil water dynamics and associated N dynamics in irrigated semi-arid cropping systems. Specifically, we learned to use the SSAT to collect water samples and analyze them for the inorganic N content. The project has helped enhance my skills in collecting soil samples and processing and analyzing them in the lab independently. Further, attending the farmer’s field days and regional crop science conference helped me improve my leadership and presentation skills and broaden my understanding. In fact, I received first place in Student Oral Competition in this year’s Western Society of Crop Science Meeting in Fort Collins Co, June 21–23, 2022. 

Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.