Nitrogen balance in dryland agroecosystem in response to tillage, crop rotation, and cultural practice

Authors: Sainju, Upendra; LENSSEN, ANDREW - Iowa State University; Allen, Brett; Stevens, William - Bart; Jabro, Jalal - Jay

Submitted to: Nutrient Cycling in Agroecosystems
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/22/2018
Publication Date: 1/27/2018
Citation: Sainju, U.M., Lenssen, A.W., Allen, B.L., Stevens, W.B., Jabro, J.D. 2018. Nitrogen balance in dryland agroecosystem in response to tillage, crop rotation, and cultural practice. Nutrient Cycling in Agroecosystems. 110:467-483. https://doi.org/10.1007/s10705-018-9909-7.
DOI: https://doi.org/10.1007/s10705-018-9909-7

Interpretive Summary: World food production will need to increase substantially over the coming decades if nutritional needs are to be met for a growing human population estimated to reach 9 billion by the year 2050. As agriculture works to meet that daunting challenge, production practices must be developed that increase food production using ecologically-based practices that reduce dependence on synthetic pesticides and fertilizers. ARS researchers at Sidney, Montana evaluated an improved cereal-based dryland cropping system designed to reduce chemical inputs, including nitrogen fertilizer, typically the largest and most costly input. The effectiveness of nitrogen management practices was evaluated by comparing nitrogen inputs to nitrogen outputs and calculating the nitrogen balance. The improved cropping system evaluated in the eight-year Montana study relied on a diverse crop rotation that included a nitrogen-fixing legume (dry pea) and an efficient fertilizer application method (sub-surface banding) to improve the nitrogen balance. Results show that crop nitrogen removal was greater while external nitrogen inputs and environmental nitrogen losses were lower with cereal-legume crop rotations compared to continuous cereal production. Tillage (conventional tillage versus no-till) and cultural practices (banded versus broadcast nitrogen fertilizer application) had little impact on nitrogen balance. The researchers concluded that diversified cereal-based crop rotations that include a legume crop are productive, use less synthetic nitrogen fertilizer, and reduce environmental nitrogen losses compared to continuous cropping systems where cereal crops are grown every year.

Technical Abstract: Accounting of N inputs and outputs and N retention in the soil provides N balance that measures agroecosystem performance and environmental sustainability. Because of the complexity of measurements of some N inputs and outputs, studies on N balance in long-term experiments are scanty. We examined the effect of eight years of tillage, crop rotation, and cultural practice on N balance based on N inputs and outputs and soil N sequestration rate under dryland cropping systems in the northern Great Plains, USA. Tillage systems were no-tillage (NT) and conventional tillage (CT) and crop rotations were continuous spring wheat (Triticum aestivum L.) (CW), spring wheat-pea (Pisum sativum L.) (W-P), spring wheat-barley (Hordeum vulgaris L.) hay-pea (W-B-P), and spring wheat-barley hay-corn (Zea mays L.)-pea (W-B-C-P). Cultural practices were traditional (conventional seed rates and plant spacing, conventional planting date, broadcast N fertilization, and reduced stubble height) and improved (variable seed rates and plant spacing, delayed planting, banded N fertilization, and increased stubble height). Total N input due to N fertilization, pea N fixation, atmospheric N deposition, crop seed N, and nonsymbiotic N fixation was greater with W-B-C-P than CW, regardless of tillage and cultural practices. Total N output due to aboveground biomass N removal and N losses due to denitrification, volatilization, plant senescence, N leaching, gaseous N (NOx) emissions, and surface runoff were not different among treatments. Nitrogen sequestration rate at 0-20 cm from 2004 to 2011 varied from 29 kg N ha-1 yr-1 in CT with W-P to 89 kg N ha-1 yr-1 in NT with W-P. Nitrogen balance varied from -73 kg N ha-1 yr-1 in NT with CW and the improved practice to 7 kg N ha-1 yr-1 in CT with W-P and the traditional practice. Because of legume N fixation and increased soil N sequestration rate, diversified crop rotations reduced external N inputs and increased aboveground biomass N removal, N flow, and N balance compared with monocropping, especially in the CT system. As a result, diversified legume-nonlegume crop rotation can be productive and environmentally sustainable compared with monocropping, regardless of cultural practices.