Response Of Soil Characteristics And Summer Maize Growth To Traffic-induced Compaction On Sandy Loam Soil In Huang-huai-hai Region

Soil compaction is widely considered as a component of soil degradation ‘syndrome',and increased farm mechanization may accelerate soil compaction in arable lands.Maize(Zea mays L.)– a sensitive crop to soil compaction – is part of summer maize-winter wheat(Triticum aestivum L.)cropping system in Huang-Huai-Hai region of China.Considerable variation in extent of field traffic-induced effects on crop growth is well documented.This variation is due to multidisciplinary nature of traffic-induced soil compaction which involves machine/soil/crop/weather interactions.Moreover,majority of the previous studies investigated this issue under worst machine/field scenarios(such as high axle load,soil moisture content more than or near field capacity)which does not necessarily represent the conditions of a common farm in region of our interest.Hence the present study was conducted under operational conditions resembling to those of local farmers(i.e.moderate machine operational specifications and field moisture content lower than field capacity)to investigate soil characteristics and summer maize growth response to field trafficking on a sandy loam soil.Two years(2016-2017)field experiment consisting of three levels of field traffic(i.e.CK,control with zero pass of intentional field traffic;C-2Wh,two traffic passes;and C-6Wh,six traffic passes)and two maize cultivars(i.e.Zhengdan-958 and Xianyu-335)was set up in randomized complete block design under split-plot arrangement.Annual field trafficking activity was carried out wheel-beside-wheel employing a 5.26 Mg vehicle before summer maize plantation when field moisture conditions were quite lower than field capacity.Prior to experiment establishment,sub-soiling(up to 25 cm depth)was performed in 2016.After field trafficking in both years,one pass of shallow rotary tillage(up to 10 cm depth)was conducted prior to manual sowing of maize in all plots including control.Soil physical parameters including bulk density,total porosity,resistance to penetration,moisture,and water-stable aggregate size distribution were determined for 10-cm soil layers up to 50 cm soil depth.Key indicators for crop growth evaluation included leaf area index,plant height,aboveground dry matter accumulation and partitioning,and grain yield and yield components.Additionally,root growth and distribution were also evaluated in 2017.Field trafficking caused topsoil compaction(< 30 cm soil profile)as indicated by significant increases in bulk density(maximum increase of 16.4%)and penetration resistance values in upper three 10-cm soil layers.Concurrently,porosity was decreased up to 17% at maximum.Moreover,the depths of peak values in nose zone for C-2Wh and C-6Wh were 22.5 and 17.5 cm as compared with 30 cm under CK in 2017.Most prominent differences among treatments appeared to be in 10-20 and 20-30 cm soil layer.Magnitude of alterations was higher in 2017 as compared with 2016.Moderate compaction(C-2Wh)slightly increased grain yield in 2016 which is reasoned as a result of sub-soiling before field trafficking in 2016.This was supported by the fact that,in general,moderate recompaction did not effect differences among compaction treatments in 2016.Absence of sub-soiling prior to field trafficking in 2017,however,resulted in negative impacts of traffic-induced soil compaction on crop growth and yield.The negative effects of soil compaction increased with number of traffic passes as yield penalty was highest(15.5%)in most trafficked treatment(C-6Wh).Compaction-induced alterations in soil physical properties,especially bulk density and penetration resistance impaired root growth and restricted root proliferation in deeper layers of topsoil;consequently,hampering crop growth and yield(yield penalty ranged 7.58%-15.50% in 2017).Most significant effects on root growth and distribution were found in 10-30 cm soil layers.Compared with control,reductions in root mass density under C-2Wh and C-6Wh were respectively 19.56% and 41.30% in 10-20 cm,37.81% and 58.30% in 20-30 cm,and 59.78% and 82.60% in 30-40 cm soil layers.Field trafficking significantly reduced leaf area index,plant height,dry matter accumulation,dry matter partitioning,and kernels number.Negative effects on plant growth indices,especially leaf area index and plant height,were more pronounced at early growth stages.Traffic-induced alterations in soil bulk density and penetration resistance in upper 30 cm soil profile were correlated to various above-and below-ground crop variables;and the negative relationships between these soil variables and grain yield were highly significant.In crux,field trafficking caused topsoil compaction even under moderate machine/soil operational conditions and effects on soil properties had a carryover effect.Though magnitude of adverse effects were not as great as previously reported for fine-textured soils under different climatic conditions and cropping systems,current study highlights the potential challenge of traffic-induced soil compaction in Huang-Huai-Hai region.This warrants further investigation to optimize farm operations by synchronizing farm machinery and soil management operations.