Annual Legume Cover Crops in Spring Wheat‐Fallow Systems

Abstract

Soil erosion is a problem in conventional tillage spring wheat ( Triticum aestivum L.)‐fallow rotations in semiarid regions. Early research using legumes to provide surface cover for erosion control in dryland crop rotations showed no yield benefits to a succeeding crop. Better residue management practices have improved fallow soil water storage and could reduce detrimental soil water influences of legumes to a succeeding crop. Objectives of our research were to determine whether field pea ( Pisum sativum . L.) and Tangier flatpea ( Lathyaus tingitunus, L.) could be grown during part of the fallow period in a hard red spring wheat‐fallow rotation to provide dry matter (DM) and surface cover for erosion control and to evaluate the influences of legumes on a succeeding spring wheat crop. Legumes were seeded during the fallow phase of a spring wheat‐fallow rotation from 1989 through 1992. During dry years, total DM and surface cover were reduced more for Tangier flatpea than field pea. Legumes produced suficient DM to exceed 35% surface cover by the flowering plant development stage when precipitation was not limiting. If growing conditions were good, legumes used soil water to a depth of 5 ft when legume growth was terminated at pod formation or grown for the full season. The N contribution to a succeeding spring wheat crop was not evident in grain N concentration or uptake. When legume growth was terminated at or before flowering, legumes provided suficient DM and surface cover to control erosion without consistent detrimental influences to a succeeding wheat crop. Research Question Soil erosion is a problem in conventional tillage crop‐fallow rotations because of lack of surface cover. Legume cover crops can provide surface cover for wind and water erosion control, but early research showed no benefit to a succeeding crop. Legume cover crops also use soil water that is needed for the succeeding crop. Objectives of our research were to determine whether field pea and Tangier flatpea could be grown during part of the 21‐mo fallow period in a spring wheat‐fallow rotation to provide dry matter (DM) for erosion control and to evaluate the influences of legumes on a succeeding hard red spring wheat crop. Literature Summary Recent research has indicated that some legume species may have potential to be used as a partial fallow cover crop in dryland cropping systems. Legumes in spring wheat‐fallow systems reduce soil erosion by providing vegetative cover when the potential for wind and water erosion are the greatest. Legumes may also reduce our dependence on commercial fertilizer. Acceptance of growing legumes during part of the fallow period has been minimal and may be due to lack of agronomic and economic knowledge of legumes in crop systems. Legumes are able to fix N from the atmosphere, but the additional N is not without cost. Use of valuable soil water to produce DM and fix N may result in failure for a succeeding crop. Legume seed cost may also exceed the cost of commercial fertilizer for an equivalent amount of N gained Gom legumes. Study Description Field pea and Tangier flatpea were seeded in late May from 1989 through 1992 during the fallow period in a hard red spring wheat‐fallow rotation. Legume vegetative growth was terminated either at flowering, pod formation, or full season (physiological maturity) plant development stages. The year after legumes, spring wheat was seeded where legumes or fallow were the previous crop. Legume treatments were compared to minimum‐till fallow. Applied Questions Will legumes provide sufficient dry matter for erosion control? Field pea and Tangier flatpea produced sufficient DM by the flowering plant development stage, during most years, to provide at least 35% surface cover. While no soil erosion measurements were made, the DM produced was assumed to be adequate for erosion control. Dry matter production was dependent on quantity and distribution of precipitation. During dry years, field pea produced more DM than Tangier flatpea but during years of about average growing season precipitation equal quantities of DM were produced. How much water does field pea and Tangier flatpea use? During near average precipitation years, field pea used 6.20 in. to flowering, 9.38 in. to pod formation, and 12.33 in. when grown the full season. Tangier flatpea used 5.07 in. to flowering, 10.67 in. to pod formation, and 12.48 in. when grown for the full season. Legumes can use water to a depth of 5 ft. Does growing legumes during part of the fallow period influence a succeeding spring wheat crop? Spring wheat grown after legumes usually resulted in less grain yield than spring wheat grown after fallow. As legumes reached maturity, spring wheat grain yields declined because water used by pea was not recharged for the succeeding spring wheat crop. When legume vegetative growth was terminated at or before the flowering plant development stage, detrimental soil water influences of legumes to a succeeding spring wheat crop were greatly reduced. Should producers consider growing legumes during the fallow period? In spring wheat‐fallow rotations, producers should consider growing a legume cover crop. Good management practices have to be followed to take advantage of the legumes and the weather. Legumes should be planted early (later April or early May) and growth terminated before flowering to reduce the detrimental soil water influences to a succeeding spring wheat crop. Long‐term benefits of having legumes in rotations included reduced soil erosion and potential increase of soil organic matter content, which results in sustainable agricultural systems.