Influence of Vehicular Traffic and Tillage Methods on Sorghum Yield in a Semi-Arid Region

INFLUENCE OF VEHICULAR TRAFFIC AND TILLAGE METHODS ON SORGHUM YIELD IN A SEMI-ARID REGION OF NIGERIA

J.O. Ohu, E. Mamman and A. Dauda

Department of Agricultural and Environmental Resources Engineering

Faculty of Engineering, University of Maiduguri, Maiduguri, Nigeria

Abstract

Field experiments were conducted for three years (2005 to 2007) to investigate the combined effects of soil compaction using tractor passes and tillage methods on soil physical properties and yield of sorghum (Sorghum l. Moench) on a sandy loam soil. The experiment was conducted at the University of Maiduguri Agricultural Engineering teaching and research farm (11° 54' N, 13° E). The soil of the study area is sandy loam with 6% silt, 17% clay and 77% sand. The treatments consisted of five levels of tractor passes (0, 5, 10, 15, 20) and four tillage methods. The tillage methods were zero tillage (ZT), ploughing (P), harrowing (H), and ploughing plus harrowing (PH). The treatments were laid out in a randomized complete block design with three replicates. The soil and plant parameters measured were soil dry bulk density, penetration resistance, soil moisture content, air permeability, plant height, and grain yield. Results over the three years of study showed that for all tillage methods, soil dry bulk density increased with increases in compaction levels. Zero tillage and zero tractor pass had the highest values of soil dry bulk density. For all compaction levels, PH gave the least values of soil dry bulk density. The results obtained for soil penetration resistance followed the same trend as that of soil dry bulk density. The values for air permeability decreased with increases in compaction levels for all tillage methods. Air permeability values were highest on PH plots irrespective of level of compaction and year. All values of soil moisture content increased from zero pass to ten passes and thereafter decreased with further increases in compaction levels. For all compaction levels, PH gave the highest values of plant height. Similarly, PH had the highest grain yield.

Keywords: soil compaction, soil bulk density, penetration resistance, air permeability, sorghum grain yield.

1.0 INTRODUCTION

Soil compaction is associated with almost all field operations when conducted under wet soil conditions. Compaction is undesirable in that it negatively influences the physical, chemical and biological properties of soils for crop production and results in conditions which are not optimum for plant growth (Mitchell and Berry, 2001). Compaction of a soil depends on the pattern of load and stress applied as well as the soil moisture content, particle size distribution, organic carbon content, aggregate stability and the initial condition of the soil prior to the application of pressure or stress ((Mitchell and Berry, 2001; Ohu et al., 2009).

Soil compaction has been defined as a detrimental modification of the pore structure when total porosity, particularly air-filled porosity is so reduced that aeration, root penetration and drainage are restricted, bulk density is increased and hydraulic conductivity and permeability are reduced (Hillel, 1980). Several studies have shown that soil compaction have adverse effects on seedling emergence, root penetration, aeration, and water and nutrients uptake. These affect crop growth and yield to a large extent (Josa and Therefter, 2005; Osunbitan et al., 2005; Simankaite, 2008; Canqui and Lal, 2008). However, there is an optimum level of soil compaction that is beneficial to crop growth and yield (Mamman and Ohu, 1997).

Many field studies have shown that the primary purpose of tillage practice is to prepare seedbed, control weeds, control insects and diseases, break out sod crops, incorporate fertilizer and manure, and to conserve moisture (Boydas and Turgut, 2007; Abid and Lal ,2009). Despite its advantages, tillage practices have some drawbacks which include; loss of organic matter, destruction of plant roots during cultivation, baring of soil surface that accelerates erosion and soil crusting, deterioration of soil aggregates, and soil compaction (Nidal and Hamdeh, 2003). The objective of this study was to evaluate the combined effects of tractor traffic compaction and some tillage methods on some physical properties of sandy loam soil and sorghum grain yield in the semi arid region of Nigeria.

2.0. MATERIALS AND METHODS

The experiment was conducted at the University of Maiduguri Agricultural Engineering Teaching and Research Farm, Maiduguri ( Latitude 110 54' N, Longitude 130 E, altitude 354 m above mean sea level). The soil of the research farm has been classified as Typic Upstisanment (Rayar, 1984). The soil has a sandy loam texture and made up of 6% silt, 17% clay and 77% sand (Ohu and Folorunso, 1989).

The experiment was laid as a factorial design involving tractor traffic and tillage methods. The experiment consisted of five levels of tractor traffic ( 0, 5, 10, 15 and 20 passes) and four levels of tillage methods (zero tillage, ploughing, harrowing and ploughing plus harrowing denoted as 0, P, H and PH, respectively) giving a total of twenty treatments.

The experiment was laid as a randomized complete block design (RCBD) with three replicates giving a total of sixty plots. The tractor passes were imposed using a Fiat 780D tractor with tyre contact pressure of 31.0 KPa; while the tillage treatments were applied using a 3- bottom disc plough and a 2-gang tandem harrow, mounted on a FIAT 780D tractor. The plot size was 10m x 10m, with 5m spacing between adjacent plots.

Soil dry bulk density was determined on undisturbed core samples using the core sampling method as modified by Blake and Hartge (1986). Core samples were taken for bulk density determinations before treatment application and at different stages of plant growth, that is, at planting, whorling, and grain maturity and harvest. Standard cone penetrometer having a cone base diameter of 15 mm and cone angle of 300 operating at 1829 mm-1 (ASAE, 1984) was used to measure the penetration resistance of the soil at a depth of 30 cm. Five penetrometer readings, were taken before treatment application; at planting, whorling, plant maturity and at harvesting. Air permeability was determined using a modified air permeameter following the principle of the air permeameter of Grover (1955). A calibrated neutron probe was used to monitor moisture content on weekly basis at 10 cm depth intervals from 25 cm to 200 cm.

Six seeds of sorghum (bicolor L.moench) variety KSV8 were planted per hole at 2.5 cm depth at a spacing of 60 cm by70 cm. The seedlings were thinned to 2 per stand at 2 weeks after emergence. Fertilizer was applied at the rate of 100-30- 30 kg ha-1 as NPK urea, SSP and Muriate of potash at planting. All the plots were hand-weeded every week throughout the growth period. Plant heights were measured with a measuring meter on weekly basis throughout the experimental period till the time of harvesting. Measurements were done from the base to the tip of the uppermost whorl using three selected plants on each plot on weekly basis for 12 weeks. Harvesting was done at maturity, 17 weeks after planting. The harvesting was done by cutting the plants at the base, the heads severed from the stalk, sun dried, threshed and the grain yield determined by weighing the threshed and winnowed grains from each plot. The grain yield per plot was converted to kg/ha.

All the data collected were subjected to analysis of variance (ANOVA) using the statistical software, Statistix Version 8.0 to compare the significance of the differences between the treatment means. Mean separation was done using Duncan's Multiple Range Test (DMRT).

3.0 Results and discussion

3.1 Effects of Tractor Traffic and Tillage Methods on Soil Bulk Density

Table 3.1 shows the effects of tractor traffic on soil bulk density. The result shows that soil bulk density increased with increase in tractor traffic for the three years of the experiment. The interaction and combination effects of tractor traffic passes and tillage treatments are also shown in the table. Bulk density increased with increase in tractor passes irrespective of the combination with tillage treatments.

The three years results consistently showed that soil bulk density successively decreased with tillage intensity. This result is in agreement with earlier findings that tillage practices reduce bulk density (Osubitan et al., 2005; Simanskaite, 2008; Elder and Lal ,2008; and Ademiluyi et al. (2009).The implication of the present study is that certain level of compaction is essential for optimum plant growth and yields.

Table 3.1: Effects of tractor traffic and tillage methods on bulk density (Mg/m3) of sandy loam soil (2005 – 2007)

Tractor Traffic Passes
Tillage method / 0 / 5 / 10 / 15 / 20 / Tillage mean
2005
Zero tillage / 1.4094fg / 1.5231d / 1.5817c / 1.6764b / 1.7194a / 1.5820w
Ploughing / 1.3567jk / 1.3817hij / 1.3883ghi / 1.3994fgh / 1.4600e / 1.3972y
Harrowing / 1.3486kl / 1.3944f-i / 1.3947f-i / 1.4553e / 1.5472d / 1.4281x
Ploughing + Harrowing / 1.3267l / 1.3497kl / 1.3717ijk / 1.4142f / 1.4592e / 1.3843z
Traffic mean / 1.3603z / 1.4122y / 1.4341x / 1.4863w / 1.5465v
2006
Zero tillage / 1.3825h / 1.5478d / 1.5906c / 1.6481b / 1.7142a / 1.5766w
Ploughing / 1.2983klm / 1.3025jkl / 1.3172jk / 1.4117fg / 1.4575e / 1.3574w
Harrowing / 1.2878lm / 1.3219j / 1.3958gh / 1.4192f / 1.5417d / 1.3933x
Ploughing + Harrowing / 1.2478n / 1.2783m / 1.3592i / 1.3825h / 1.4058fg / 1.3347y
Traffic mean / 1.3041z / 1.3626y / 1.4157x / 1.4653w / 1.5298v
2007
Zero tillage / 1.3089lm / 1.4956e / 1.5628c / 1.6406b / 1.7189a / 1.5453w
Ploughing / 1.2706n / 1.3047lm / 1.3211kl / 1.4158h / 1.4753f / 1.3575y
Harrowing / 1.2778n / 1.3372jk / 1.3678i / 1.4653f / 1.5231d / 1.3942x
Ploughing + Harrowing / 1.2747n / 1.2964m / 1.3419j / 1.4092h / 1.4447g / 1.3534y
Traffic mean / 1.2830z / 1.3585y / 1.3984x / 1.4827w / 1.5405v
Combined mean
Zero tillage / 1.3669hi / 1.5221d / 1.5783c / 1.6550b / 1.7175a / 1.5680w
Ploughing / 1.3085kl / 1.3296jk / 1.3422ij / 1.4090fg / 1.4643e / 1.3707y
Harrowing / 1.3047kl / 1.3512ij / 1.3861gh / 1.4466e / 1.5373d / 1.4052x
Ploughing + Harrowing / 1.2831l / 1.3081kl / 1.3576hij / 1.4019g / 1.4366ef / 1.3575y
Traffic mean / 1.3158z / 1.3778y / 1.4161x / 1.4781w / 1.5389v

Means followed by similar superscript letter(s) a-n for treatment combinations, v-z for traffic and w-z for tillage are not significantly different at 1% probability level of the Duncan’s Multiple Range Test.

3.2 Effects of Tractor Traffic and Tillage Methods on Penetration Resistance

The combination effects of tractor passes and tillage treatments on penetration resistance are shown in Table 3.2. Penetration resistance increased with increase in tractor passes irrespective of the combination with tillage treatments. The zero tillage at different tractor passes has the highest penetration resistance followed by ploughing at different tractor passes. Harrowing at different tractor passes followed by ploughing and harrowing at different tractor passes resulted in the least penetration resistance.

The highest value of penetration resistance produced at zero tillage irrespective of tractor traffic for 2005 was 2.08MPa while that for 2006 was 2.07MPa, and the 2007 result was 1.91MPa. The difference in the values of penetration resistance recorded over the three year- period was attributed to differences in rainfall amount experienced in the three years.

Effects of tillage methods on soil penetration resistance varied significantly (P<0.01). The three years results showed that penetration resistance of all tillage treatments was significantly lower than that of untilled field (Zero tillage). In general, soil penetration resistance increased with increase in compaction level, but decreased with tillage intensity. Similar results have been reported (Thierefter et al, 2005; Truckman et al, 2008; Czyz, and Dexter 2009) that soil compaction from tractor traffic increased soil penetration resistance while tillage reduced penetration resistance.

Table 3.2: Effects of tractor traffic and tillage methods on soil penetration resistance (MPa) of

sandy loam soil (2005 – 2007)

Tractor Traffic Passes
Tillage method / 0 / 5 / 10 / 15 / 20 / Mean
2005
Zero tillage / 0.6106jk / 1.4450g / 1.7344e / 1.9606b / 2.0794a / 1.5660w
Ploughing / 0.4747mn / 0.5244l / 0.5886k / 0.6872i / 0.7703h / 0.6091z
Harrowing / 0.4775mn / 1.4028g / 1.5961f / 1.8194d / 1.9100c / 1.4412x
Ploughing + Harrowing / 0.4506n / 0.5156lm / 0.6356j / 0.7717h / 0.7856h / 0.6318y
Traffic mean / 0.5033z / 0.9719y / 1.1387x / 1.3097w / 1.3863v
2006
Zero tillage / 0.7100fg / 1.4861e / 1.7083cd / 1.9461b / 2.0786a / 1.5858w
Ploughing / 0.5436i / 0.6025hi / 0.6439gh / 0.7158fg / 0.7636f / 0.6539y
Harrowing / 0.6072hi / 1.4039e / 1.6258d / 1.7489c / 1.8975b / 1.4567x
Ploughing + Harrowing / 0.5361i / 0.5947hi / 0.6567gh / 0.7339fg / 0.7703f / 0.6583y
Traffic mean / 0.5992z / 1.0218y / 1.1587x / 1.2862w / 1.3775v
2007
Zero tillage / 0.6711m / 1.4425e / 1.5528cd / 1.7153b / 1.9114a / 1.4586w
Ploughing / 0.5811n / 0.6983m / 0.8753jk / 0.9392ij / 1.0522h / 0.8292y
Harrowing / 0.8150kl / 1.3269f / 1.2417g / 1.5364d / 1.6069c / 1.3054x
Ploughing + Harrowing / 0.5789n / 0.7961l / 0.8794jk / 0.9683i / 1.0397h / 0.8525y
Traffic mean / 0.6615z / 1.0660y / 1.1373x / 1.2898w / 1.4026v
Combined mean
Zero tillage / 0.6639ij / 1.4579e / 1.6652d / 1.8740b / 2.0231a / 1.5368w
Ploughing / 0.5331k / 0.6084jk / 0.7026hij / 0.7807fgh / 0.8620f / 0.6974y
Harrowing / 0.6332ijk / 1.3779e / 1.4879e / 1.7016cd / 1.8048bc / 1.4011x
Ploughing + Harrowing / 0.5219k / 0.6355ijk / 0.7239ghi / 0.8246fg / 0.8652f / 0.7142y
Traffic mean / 0.5880z / 1.0199y / 1.1449x / 1.2952w / 1.3888v