Innovations in Dryland Agriculture

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4 Effects of Crop Residue and Nutrient Management

Practices on Soil Organic Carbon

Decisions on crop residue management practices in dryland cropping systems are
mainly influenced by agroecological and agronomic considerations. Crop residues
are managed by burning, harvest and removal, or incorporation by tillage. Burning
is practices on about 1.24 × 10^6 ha of cropland in the contiguous U.S. annually.
Although most of the burned acreage is under grassland production some dryland
farmers use burning. For example, burning is used on about 30,000 ha of dryland
farms in the IPNW (McCarty et al. 2009 ). Residue management practices such as
burning residue and intensive tillage are not sustainable in dryland areas. In these
areas, soils are highly vulnerable to wind and water erosion and loss of soil organic
matter, especially in a wheat-summer fallow rotation where only one crop is pro-
duced in two years.
Concern about erosion and soil degradation have led to an evolution of tillage
practices (Table 2 ) in North American dryland that were designed to leave crop resi-
dues in the field during fallow periods and cultivate soil in spring using disc or sweep
plows. Reduced tillage practices such as stubble mulching leaves about 10–20 %
surface cover, whereas no-till can leave as much as 50 % cover. While this cover is
highly beneficial for soil conservation, there are some challenges. Under these high
residue systems seed emergence is reduced due to lack of good seed-soil contact and
increased disease incidences such as Rhizoctonia and Pythium (Paulitz 2006 ).
Emergence and early season growth can be slow due to cooler temperatures and N
deficiency caused by N tie-up due to high C:N ratio of the wheat straw (80:1). Thus,
tillage decisions in dryland cropping systems must weigh the advantages of soil and
water conservation against the potential direct and indirect costs of the systems.
Results of a long term study can shed light on the sustainability of various crop
residue management practices. The crop residue long-term experiment (CR-LTE)

Table 2 Summary of the general properties of three categories of tillage practices

Tillage systema

Tillage

depth (cm)

Residue

management

cover

Soil organic carbon

Loss/gain (%)

Soil

erosion +/− Literatures

Conventional

tillage

20 cm < 15 % Loss – 0.22–0.42 Mg

ha−^1 year−^1

− Machado

( 2011 ) and

Williams and

Wuest ( 2011 )

Reduced tillage < 20 cm 15–30 % + Schillinger

and Young

( 2014 )

No-tillage Surface/

None

>30 % Predicted gain – 0.12–

0.21 Mg C ha−^1 year−^1

in 10–12 years

• Brown and
  Huggins
  ( 2012 )
  aTillage system

Dryland Agriculture in North America