Soil Compaction Varies by Long -Term Application of Barley Straw in Paddy Field.

Soil compaction is becoming a greater problem for crop production in intensely cropped area because intensive cropping systems generally require more cultural operations, which result in a greater frequency of vehicle and implement passage and greater opportunity for additional compaction to occur . Cropping system and organic matter affect crop productivity and soil chemical-physical properties. The effects of crop residues and cropping system on soil compaction have been documented as individual factors, understanding on their interactions limited. Such understanding is needed to prevent soil compaction and optimize soil management practices. Soil compaction, which relates to the resistance to penetration of a cone of specific dimension, is an important physical property relating to soil and crop productivity, particularly in intensive cropping systems. The level of agricultural productivity in Korea has been increased by double cropping system. Most rice and barley straw are utilized as feeds to livestock by recovering them from the fields. Soil physical properties and strength for Korean paddy fields have been conventionally subjected to uniform-depth tillage over the entire field, the depth to the hardpan was limited up to only about 17.6cm, hardness of compaction layers index was 21.1mm, and thickness of plow pan were distributed from 5 to 17cm, showing both minimum and maximum values. However, the long-term effect of alternative residue management practices, particularly those associated with the popular rice-barley double crop system in Korea paddy field on soil Cone Index (CI) have not been thoroughly investigated. Therefore, the objective of the study was to quantify the impacts and interactions of residue management on organic carbon and physical properties such as bulk density (BD) on the soil compaction by long-term application of crop residue as quantified by CI and CI-related variables. This experiment was conducted on a long-term (20 years) experiment field of rice- barley cropping system established in Department of Functional Crop, NICS, RDA. The soil at site was Pyeongtaeg series which is a member of the fine silty, mixed mesic, nonacid family of Typic Endoaquepts (Low Humic-Gley soils) developed from alluvium on broad continental alluvial plains according to Korean Soil Taxonomy (NIAST. 2000).

Cropping systems (CS) were established in 1990 to investigate the effects of double cropping system and residue management practices on crop production and soil and soil organic carbon (SOC). The experimental design was a randomized complete block with three blocks (i.e., replications) where all rotation phases of each CS were present each year. Each of plots measured 11.4 m 82 m (0.94 ha). Treatments consisted of three different cropping systems practices [RMCS; rice (Oryza sativa L.) mono cropping system, RBSR; rice-barley (Hordeum vulgare var.) straw removal, RBSI; rice-barley straw incorporation]. The penetration resistance was measured using a static hand operated recording penetrometer (Eijkelkamp, Giesbeek, The Netherlands) (Lowery and Morrison, 2002) having cone base area of 1 cm² and an apex angle of 30°Æ. CI data obtained from the literature were further classified the shapes of CI profiles for analysis the effect of crop residue management by (1) Min CI (Min CI, MPa) (2) Maximum CI (MCI, MPa), (3) Depth to the MCI (DCI, cm), (4) Depth to 2 MPa (D2CI, cm), (5) Thickness of the soil layer with CI > 2 MPa (TD2CI, cm)Soils were sampled at the same time for soil moisture content (SM) and soil bulk density (BD) measurements. Mean differences for response variables were examined using F-protected LSD (a=0.05).

The results showed that the SOC in the upper 12cm depth of soil at RBSR and RBSI did not significantly differ. On the other hand, BD and CI were found to decrease at RBSI. The BD of the upper 30cm depth of soil at RBSI was significantly different from the other treatments. The Min CI by 0-15cm for RMCS was 0.54 MPa, for RBSR was 0.42 MPa and for RBSI was 0.39 MPa. Residue removal management had significantly greater penetration resistance than any residue incorporation. The D2CI by residue incorporation was deeper as 23cm at RBSI plots than 19 cm of RBSR and 15cm of RMCS. And the MCI by cropping system was lower as 1.90 MPa at RBSI than 2.20 MPa of RBSR and 2.21 MPa of RMCS. Thick of 2 MPa (D2CI) showed around 10 cm at RBSI plots, 21 cm at RMCS. Therefore, RBSI exhibited the MCI the deepest layer to 2 MPa and the thinnest 2 MPa thickness comparable to RBSR and RMCS. And RBSI was more effective than RMCS in increasing soil organic carbon for the improvement of soil fertility and physical properties in paddy fields of South Korea.

Keywords: Compaction, Penetrometer, Cone index, Bulk density, Double cropping system, Long –Term