Synchrony and Contribution of Legume Nitrogen for Grain Production Under Different Tillage Systems

Project Overview

Project Type: Research and Education
Funds awarded in 1989: $95,081.00
Projected End Date: 12/31/1994
Region: North Central
State: Kansas
Project Coordinator:
John Havlin
Kansas State University

Annual Reports


  • Agronomic: sorghum (milo), wheat, hay


  • Animal Production: feed/forage
  • Crop Production: crop rotation


    [Note to online version: The report for this project includes tables and figures that could not be included here. The regional SARE office will mail a hard copy of the entire report at your request. Just contact North Central SARE at (402) 472-7081 or]

    The benefits of crop rotations on agricultural productivity have long been known and are an important component of sustainable agriculture. Legumes in rotation can provide significant quantities of N to succeeding non-leguminous grain crops. Research was initiated on a Reading silt loam at 2 sites to determine the contribution and synchrony of legume N from soybeans, hairy vetch, and red clover for grain sorghum, and from hairy vetch, sweet clover and alfalfa for winter wheat, under conventional and no-tillage residue management. Nitrogen rates of 0, 60, and 120 kg N ha-¹ were applied to sorghum following legumes. Nitrogen rates of 0, 30, and 60 kg N ha-¹ were applied to wheat in 1991, and 0, 50, and 100 kg N ha-¹ to wheat in 1992 following legumes. The rotational benefit gained from legumes in these rotation were highest following hairy vetch (wheat and sorghum) and red clover (sorghum) and sweet clover (wheat). Residual rotational benefit was also greatest from hairy vetch. At site 1 in 1991 sorghum yields were highest following continuous sorghum. Due to the advanced maturity of sorghum following hairy vetch and red clover in 1991, more of the grain filling period of sorghum following these crops was subjected to drought conditions which reduced yields. Sorghum yields were highest following hairy vetch and red clover at site 2 in 1992. Wheat yields in 1991 following hairy vetch were lower than following the other previous crops because the high N availability following hairy vetch contributed to extensive powdery mildew infection the reduced grain yield. Tillage did not significantly influence grain yield. Nitrogen uptake patterns were similar for both tillage systems and both years. Generally, N uptake increased with N rates. At the beginning of the growing season, soil nitrate levels were highest following hairy vetch, sweet clover and red clover in both years. Increased soil nitrate levels during much of the maximum sorghum N uptake period in 1992 suggested that N synchrony was better than in 1991 when soil NO3–N decreased after the initial sampling. The reverse was true for winter wheat.

    The critical component of these rotations is legume establishment. Under the proper growing conditions, hairy vetch, sweet clover and red clover have the ability to fix large quantities of N and supply most or all the N a wheat or sorghum crop requires. In order to maximize the efficiency of the rotation, synchronization of N mineralization with wheat and sorghum N uptake is important but will vary between years.

    Project objectives:

    1. Quantify nitrogen (N) mineralization from forage and grain legumes and subsequent N availability to non-legume grain crops.

    2. Evaluate the influence of tillage on the quantity of N mineralization and availability to grain sorghum and winter wheat.

    3. Describe and quantify the synchrony of soil and legume N mineralization and N uptake by non-legume grain crops.

    4. Evaluate the potential use and N balance of mono- and poly-culture production of perennial grain crops.

    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.