Effect of Compaction and Irrigation Regimes on Soil Physical Characteristics, Emergence, Growth and Productivity of Summer Moongbean

The unfavorable effects of compaction on soil health and crop productivity are much greater today than in the past because of immense increase in use of heavy farm equipments. Excessive use of heavy implements can cause deterioration of soil physical environment and structure. Soil compaction results in increased bulk density and penetration resistance and reduced infiltration. Mada et al., (2013) observed that compaction slowed down the rate of seed germination as it did not allow proper contact between seed and soil. Further it impeded the root growth, thus affecting the plant’s ability to take up nutrients and water from subsurface soil (Bengough et al., 2006). Soil compaction reduces the crop growth and yield, by restricting root development as well as water and air movement in the soil (Alameda and Villar, 2009). Aase et al., (2001) reported that as cone index approaches 2.0 M Pa and moves above this value, root growth is restricted to varying degrees. Soil compaction can have adverse effect upon crops by increasing the mechanical impedance to the growth of roots; altering the extent and configuration of the pore space (Becerra et al., 2011; Chen and Weil, 2011; Li et al., 2012). Summer moongbean (Vigna radiata L.), cultivated in Punjab during mid-March to end June has a good potential under irrigated conditions due to high evapotranspiration rates and scarce water supply in this period. However, its growing season particularly the reproductive phase coincides with the harsh weather conditions and warrant attention for high yield realization. First irrigation at 15 days after sowing (DAS) and subsequent irrigation at weekly intervals recorded the highest plant height, plant dry matter, yield attributing characters and grain yield (Aulakh and Vashist, 2007). Yadav and Singh (2014) reported highest grain yield along with other growth attributes under more frequently irrigated water regimes. Furthermore, irrigation may reduce the impact of soil compaction (Vaz et al., 2013) as irrigation affects the pore structure of soil and water infiltration capacity by manipulation of hydraulic stresses (Peng et al., 2007). Therefore, it is required to specify optimum irrigation regime and its effect on compaction levels for achieving maximum productivity. Thus, the aim of the current investigation was to study the impact of soil compaction and different irrigation regimes on soil physical characteristics and growth and productivity of summer moongbean in loamy sand soil.

Experimental Site and Treatments

A field experiment was conducted at the Research farm of the Department of Soil Science, Punjab Agricultural University, Ludhiana, India (30°54'N, 75°48'E, 247 m above mean sea level) in 2017 and 2018 summer cropping seasons. The soil at experimental site was neutral, non-calcareous in nature and alluvial loamy sand in texture (Typic ustochrept) developed under hyper-thermic regime. Important soil physical and chemical characteristics are presented in Table 1. The groundwater level was more than 20 m deep. Weather information during the cropping seasons is given in Table 2. Total rainfall during the cropping seasons of 2017 and 2018 was 214.2 and 170.8 mm; while corresponding cumulative pan evaporation was 867.4 and 622.3 mm. Pan evaporation during both the cropping seasons was lower than the normal values; contrary to this rainfall was more. The actual rainfall during cropping duration in 2017 and 2018 was 118 mm and 145 mm. Mean maximum and minimum air temperatures during different growing seasons varied between 27.2-39.1°C and 12.-26.6°C.





Combinations of compaction levels and irrigation regimes were evaluated in a split-plot design with compaction in the main plot: three compaction levels i.e. zero (C0), one (C1) and three (C3) roller passes and in the sub plots three irrigation regimes i.e. irrigation water (IW) to pan evaporation (Ep) ratios of 0.4 (I0.4), 0.6 (I0.6) and 0.8 (I0.8) with three replications. The main plot size was 120 m² and sub plot size was 35.7 m². In no compaction plot, the sowing was done after seed bed preparations. While in single and three roller passes the crop was sown after seed bed preparations, thereafter different levels of compaction were accomplished with roller having weight 1000 kg; width 1.2 m and circumference 1.6 m. The cultivar SML-866 was sown in the last week of March @ 25 kg ha^-1 with heavy pre-sowing irrigation for both the years. The seed was placed at 6 cm deep with a row spacing of 22.5 cm and plant spacing of 7 cm. Before seeding, the seed was treated with fungicide Captan @ 3 g kg^-1 seed. The seed was inoculated with freshly prepared Rhizobium culture at the time of sowing. Nitrogen @ 12.5 kg ha^-1 and phosphorous (P₂O₅) @ 40 kg ha^-1 were applied through urea and single super phosphate, respectively as a basal dose. For both the years the number of post sowing irrigations (70 mm each measured with Parshall flume) applied in I_0.4, I_0.6 and I_0.8 regimes were three, four and five, thus, the amount of irrigation water applied was 210 mm, 280 mm and 350 mm, respectively. The crop was harvested in the last week of June.
 
Measurements
 
Undisturbed soil bulk density (ρb) was measured with the help of core having diameter and height of 5.0 cm at 0-5, 5-10, 10-15 and 15-20 cm depths with three replications at the time of harvest. The cores were dried in an oven at 105°C till the weight of the soil becomes constant. Soil bulk density (ρb, Mg m^-3) was calculated as the ratio of dry soil mass (Ms) and internal volume (Vt) of the core (Blake and Hartge, 1986).
 
     
In-situ infiltration rate was measured by double-ring infiltrometer according to method described by Reynolds et al., (2002) at the time of harvest.

Seed emergence count (No. m^-2) was recorded at 5, 10, 15 and 20 days after sowing (DAS) in each plot. At harvest, five plants were selected randomly from each plot for recording plant height, number of pods plant^-1 and number of seeds pod^-1. From each plot weight of one thousand seeds was recorded and expressed as 1000-seed weight (g). The seed yield of each plot was recorded from the net area of 4 m² and expressed as t ha^-1. The straw yield was calculated by subtracting the seed yield from biological yield for each plot, recorded before the threshing of the crop, and expressed as t ha^-1. The irrigation water productivity was calculated by dividing the seed yield of corresponding treatment with the amount of irrigation water applied (mm) in particular treatment.

Soil cores for determining root growth were sampled at 55 DAS at 10 cm depth increments down to 70 cm soil depth with 5 cm diameter auger centred at 4 cm away from plant base (Gajri et al., 1994). Roots from each sample were washed in net cloth, cleaned and length of roots was measured by a scanner (CI 202 model of CID Bio Science make USA). The root length density (RLD, cm cm^-3) was calculated from the total length of roots to internal volume of the core.

Treatment effects on various parameters were tested for their statistical significance using ANOVA for a split-plot design as prescribed by Cochran and Cox (1967) and adapted by Cheema and Singh (1991) in statistical package CPCS-I. The treatment mean comparisons were made at 5 percent level of significance. Standard deviations were computed for soil bulk density.

Bulk density and infiltration rate

Among mechanical characteristics soil bulk density is mainly affected by compaction. The data regarding compaction effect on soil bulk density is presented in Fig 1. It revealed that with increase in compaction the soil bulk density increased. In 2017, for surface soil (0-5 cm) it varied from 1.50 at C₀ to 1.56 Mg m^-3 at C₃. Similarly, at 5-10 cm depth it increased from 1.53 to 1.62 Mg m^-3. Similar trend was observed in 2018, bulk density increased by 4.6% for 0-5 cm and 6.5% for 5-10 cm at C₃ than C₀. Below this depth the difference in bulk density diminished due to soil compaction and it remained almost unchanged at 15-20 cm. Blanco-Canqui et al., (2004) also reported that wheel traffic increased bulk density by 6 per cent. Compaction increases bulk density by disrupting soil aggregates or by compression of soil aggregates forming restrictive layer and thus decreases soil volume (Badalikova and Hruby, 2006).



The effect of compaction on infiltration rate of soil is presented in Fig 2. It decreased from 2.4 cm hr^-1 at C0 to 1.6 cm hr^-1 at C₃ compaction level in 2017. Likewise in 2018, compaction affected infiltration rate with a decrease from 2.4 cm hr^-1 at C₀ to 1.6 cm hr^-1 at C₃. Compaction of soil aggregates causes reduction in the pore space being occupied by water and air. In addition to pore space, pore size is also reduced which consequences in restricted water and air movement, thus affecting the hydraulic properties of soil (Vidinamo et al., 2010). Abo-Abda and Hussain (1990) also reported 30% reduction in infiltration of sandy soil due to compaction.


 
Emergence count
 
Uniform emergence of seed is a pre-requisite for attaining higher crop yields. The data on emergence count m^-2 for 2017 and 2018 is presented in Table 3. Soil compaction had a significant effect on the seed emergence count of summer moongbean during both the years. In 2017, the emergence count was reduced by 84, 45.7, 18.7 and 17.7% at 5, 10, 15 and 20 DAS respectively. In 2018 also, compaction caused a reduction of 38.2-19.4% in emergence count from 5 to 20 DAS. On an average, maximum reduction was observed at 5 DAS, when emergence count of 22.4 m^-2 in non-compacted plots (C₀) which was lowered by about 57% with compaction (C₃). On the other hand, irrigation had non-significant effect on emergence count till 1₀ DAS but at 15 DAS, a significant effect irrespective of the compaction was observed during both the cropping seasons; the corresponding increase in seedling count was 18.7 and 24.7% in I_0.8 as compared to I_0.4 due to irrigation water input in former regime. Compaction reduces porosity by moving soil particles close together, restrains air-water movement through soil and decreases water holding capacity of soils (Motavalli et al., 2003) and amount of oxygen content required for energy metabolism during the process of germination (Masaka and Khumbula 2007), resulting in negative impact on the emergence count. The interactive effect of compaction and irrigation was observed in 2018 and average of two years. Irrigation regime I₀.8 might have provided the sufficient moisture to the seeds, thus resulting in significant increase in emergence count by 33.1 and 42% over I_0.4, at C₁ and C₃ compaction levels, respectively whereas at C₀, emergence count was at par in all the irrigation regimes.


 
Plant height
 
Plant height is an index of growth and development, representing the infrastructure build-up by the plant over some time. The data pertaining to plant height presented in Table 4 reveals reduction in plant height with an increase in soil compaction level during both years. Irrespective of irrigation regimes, plant height reduced significantly by 17.6 and 18.4% at C₃ than C₀ during 2017 and 2018 respectively. Amongst irrigation regimes, maximum plant height was observed in I0.8 regime i.e. 47.6 and 46.4 cm in 2017 and 2018, respectively, while, the corresponding values for I_0.4 irrigation regime were 39.1 and 38.1 cm. Yadav and Singh (2014) observed an increase in plant height with an increase in the frequency of irrigations. Kirnak et al. (2016) also observed similar trend of decreasing plant height with increase in compaction level from low to high. Reduction in air filled porosity by compaction affects the oxygen content and may cause anaerobic conditions in soil. In addition, intermittent aerobic and anaerobic conditions during and between irrigation events in compacted soils may lead to enhancement of denitrification process or loss of nitrogen. Thus, impeded nitrogen content in soil along with reduced ability of roots to take up nutrients can be attributed to reduced plant height in compacted soils.
 
Yield attributing traits
 
The data pertaining to yield attributing traits viz. number of pods plant^-1, number of seeds pod^-1 and 1000-seed weight is presented in Table 4. Considering the main factor compaction levels, number of pods plant^-1 was maximum at C₁ (27.4 and 24.9) followed by C₀ (22.3 and 20.3) and C₃ (17.1 and 16.2) during both the years respectively. While considering irrigation levels, number of pods plant^-1 increased significantly with increase in frequency of irrigations from 19.8 (I_0.4) to 24.9 (I_0.8) in 2017 and from 17.2 (I_0.4) to 23.1 (I_0.8) in 2018. The number of seeds pod^-1, is considered an important factor as it deals with the potential yield recovery in leguminous crops. The highest number of seeds pod-1 i.e., 10.2 and 9.1 was observed in C₁ compaction level during 2017 and 2018 respectively. However, corresponding values recorded at C₀ (9.1 and 8.3) and C₃ (8.6 and 7.9) compaction level were at par but significantly lower than C₁. The number of seeds pod^-1 was highest in I0.8 regime (9.9 and 9.3), which was statistically at par with irrigation schedule I_0.6 regime (9.1 and 8.8) but, was significantly higher than I_0.4 irrigation regime (8.9 and 7.2) in 2017 and 2018, respectively. Similar pattern was observed for 1000-seed weight with significantly higher values (41.9 and 40.4 g) observed under C₁ compaction level as compared to C₀ (39.5 and 36.2 g) and C₃ (38 and 35.1 g) compaction levels during both the cropping seasons. 1000-seed weight was 8.1 and 14% higher in the respective crop seasons, when irrigated with I_0.8 regime as compared to I_0.4. The positive response of yield attributing traits to one roller pass (C₁) can be attributed to the effect of compaction on water holding capacity of sandy loam soils. Also, higher number of pods under I_0.8 might be due to better moisture regime, while in I_0.6 and I_0.4, moisture stress conditions might have led to flower drop, thus reducing the number of pods. Our results are in corroboration with the findings of Yadav and Singh (2014) who also reported an increase in the number of pods per plant with an increase in a number of irrigations.


 
Root length density
 
The data depicting the effect of compaction levels on root length density is presented in Fig 3. It reveals that with increase in soil compaction level though the root length density decreased at the surface layer, it increased at subsurface soil layers. In no compaction plots, maximum root length density 1.35 and 1.31 cm cm^-3 was recorded in the surface soil layer which decreased to 1.12 and 1.16 cm cm^-3 in C₃ plots during 2017 and 2018, respectively. While comparison at 20 cm depth reveals that root length density was higher in C₁ plots (1.32 and 1.28 cm cm^-3) in comparison to C₀ (1.17 and 1.09 cm cm^-3) in 2017 and 2018 respectively. Abu-Hamdeh (2003) also reported that compacted plots had greater concentration of roots near the base of the plants in comparison to zero-load plots. Compaction increased bulk density, added to soil strength along with the retention of soil moisture for crop use, thus confining the roots almost entirely to the top 60 cm of soil (Laboski et al., 1998). RLD values were at par for the three irrigation regimes.


 
Straw yield
 
The data on effect of different irrigation and compaction level on straw yield is presented in Table 5. The straw yield under C₁ compaction level was found to be significantly higher as compared to C₃ (14.6 and 16.6%) and C₀ (8.3 and 8.7%) during both the years respectively. Straw yield of moong was significantly influenced by different irrigation schedules. Irrigation regime of I_0.8 produced maximum straw yield (6.21 and 5.91 t ha^-1) being significantly higher than I_0.6 (5.63 and 5.37 t ha^-1) and I0.4 (5.20 and 4.89 t ha^-1) irrigation regimes. The reason for increased biomass yield under more frequently irrigated regimes might be due to more efficient photosynthesis as the evapo-transpirational demands were fulfilled better under this and the plants produced more dry matter, leaf area and ultimately higher biomass yield (Trivedi et al., 1994). The interaction of compaction and irrigation was significant in 2018 with maximum straw yield (6.37 t ha^-1) in C₁ under I0.8 regime. There were about 17 and 30% increase in straw yield under I0.8 regime as compared to I_0.4 in C₁ and C₃ compaction levels respectively.

Grain yield
 
The data regarding summer moongbean grain yield as affected by compaction level and irrigation scheduling is presented in Table 5. The data reveals that grain yield was higher in 2017 than 2018 though difference was non-significant. Among different compaction levels, maximum grain yield was recorded at C₁ i.e. 1.38 and 1.27 t ha^-1 in 2017 and 2018 respectively while the minimum grain yield was observed at C₃ compaction level i.e. 1.22 and 1.08 t ha^-1 in the respective years. The mean grain yield decreased up to 6.9 and 16% in C₃ as compared to C₀ and C₁ respectively. The highest grain yield obtained under C₁ might be due to a higher number of pods per plant, seeds per pod and 1000-seed weight as compared to C₃ and C₀ compaction. Kirnak et al., (2013) also reported yield loss up to 45% with high compaction levels. Considering the effect of irrigation on grain yield, highest yield (1.36 t ha^-1) was recorded under I_0.8 irrigation regime, which was statistically higher by 22% than I_0.4 and 14% than I_0.6 irrigation regime. So, it is apparent that increased moisture availability of soil increased grain yield. Yadav and Singh (2014) also observed a similar trend in seed yield with increase in irrigation frequency.


 
Irrigation water productivity
 
Irrigation water productivity (IWP) is the measure of economic yield of crop obtained per unit amount of irrigation water used by the crop. The data on irrigation water productivity of moongbean is presented in Table 5. The data reveals that during 2017 and 2018, maximum IWP i.e. 5.11 and 4.70 kg ha^-1 mm^-1, respectively was recorded at C₁ compaction level irrespective of irrigation regimes. The corresponding values at C₀ were 4.70 and 4.29 kg ha^-1 mm^-1 while at C₃, 4.46 and 3.94 kg ha^-1 mm^-1. On an average of two years IWP was higher at C₁ (4.90 kg ha^-1 mm^-1) followed by C₀ (4.50 kg ha^-1 mm^-1) and C₃ (4.20 kg ha^-1 mm^-1). Higher water productivity with C₁ level resulted from significantly higher grain yield as compared to other levels. Among irrigation regimes, highest value of IWP (5.4 kg ha^-1 mm^-1) was obtained under I_0.4 irrigation regime. This can be attributed to efficient use of applied water and relatively more grain yield per unit water applied. The water productivity decreased with increase in irrigation level. The lowest water productivity (4.4 and 3.8 kg ha^-1 mm^-1) was recorded in I_0.6 and I_0.8 irrigation regime, respectively because the proportionate increase in grain yield was lower. These results are in similarity with the findings of Soni and Gupta (1999) and Yadav and Singh (2014).

The results indicated that maximum grain yield and yield attributes were recorded at C₁ compaction level. Amongst irrigation regimes I_0.8 recorded maximum yield. As expected, the irrigation water productivity was highest in I_0.4 irrigation regime. This study suggested that C₁ compaction i.e, one roller pass in loamy sand soil with I0.8 irrigation regime may be useful for achieving higher productivity in summer moongbean.