Pore Size Distribution of Soil Treated with Different Plowing Depths and its Relationship to the Efficiency of Water Use for Corn

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Nameer T. Mahdi, Ali H.A. Al-Aridhee

Abstract

The soil pore size distribution is one of the propertiesthat directly affect water infiltration, hydraulic conductivity, and water holding capacity. Soil tillage often results in an unstable soil structure with an increase in the percentage of drainage pores between soil aggregates, which change with time due to the wetting and drying cycle, soil solution components, agricultural processes, and biological activity, as well as the change of water conductivity with time.In order to test the effect of the plowing depth on the soil pore size distribution, an experiment was carried out in a silty clay loam in the Nile sub-district of Babylon Governorate, south of Baghdad, Iraq, with four plowing depths. The first treatment was No-tillage (T0), and Minimum tillage usingspike pin harrows, at a depth of 0.10 m (T1). The chisel plowwas used for plowing with two depths of 0.20 m and 0.30 m, which represented treatments (T2),and (T3), respectively. Irrigation was carried out by applying three irrigation systems which are surface drip irrigation I1, subsurface drip irrigation I2 and basin irrigation I3.Soil water retention curve (θ(h)) was estimated for field soil. Then, a computer program (RETC code) was used to match the pressure head data h against the volumetric watercontent θ of a non-linear relationship to estimate the van Genuchten equation parameters, [α, n, and m given that m=1-(1/n)]. Besides, The effective pore diameter (D) was calculated from the Young-Laplace equation.The results showed that whenever the depth of plowing increased, the percentage of air pores increased, as the treatments T2 and T3 had the largest proportion of air-filled pores, while the treatments T0 and T1 had the lowest percentage of air pores ranging between 0.091 and 0.165 cm3 cm-3. At the same time, it had the largest proportion of available water-filled pore, with an average rate of about 0.217 cm3 cm-3, which is available water tomeet water requirements for maize.The treatments T0 and T1 contributed to reducing the added irrigation water by 12.41% compared to the treatments T2 and T3, and reducing the frequency of irrigation when applying subsurface drip irrigation I2 compared to the irrigation systems I1 and I3. Furthermore, it gave the highest grain yield of maize, with an average of 9000 kg.ha-1, which positively affected increasing the maize wateruse efficiency, as the average water use efficiency was about 3,319 kg.m-3atsubsurface drip irrigation.

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