Continuous clay skins are found on ped faces, in pores, and around root channels in the B22t horizon of Cecil soils in North Carolina. Thicker, discontinuous clay skins are also observed along vertical pores in the Cl horizon. Compared to the whole peds from the B22t horizon the clay skins contain more clay, fine clay (<0.2µ), total iron, free iron, Al2O3, K2O, P2O5, and total nitrogen; less silica and gibbsite than the whole soil peds. The fine clay fractions (<0.2µ) of the A2 horizon and the clay skins of the B22t horizon are similar, both being finely divided and poorly crystalline compared to the fine clay from the whole peds of the B22t horizon and the clay skins in the Cl horizon.
A greenhouse experiment was conducted to study the effect clay skins may have on plant growth and N, P, and K uptake. Wheat (Triticum vulgare, var. Wakeland) plants were grown in uncoated aggregates and in large and small clay skin‐coated peds from the B22t horizon of a Cecil (Typic Hapludult) soil for 4 weeks. Data obtained for dry weight and total N, P, and K content of the plants were statistically analyzed. Plants grown in the uncoated aggregates had higher dry weights and more total N, P, and K than those grown in either the large or small coated peds. Most of the plant roots grew outside of the coated peds with a concentration of fine roots on the surface of the clay skin. It is hypothesized that the clay skins reduced plant growth and nutrient uptake (especially P and K) either by serving as a barrier for root growth and/or by slowing ion diffusion from the soil peds into the inter‐ped soil solution.
A field experiment has taken place in Wahet El-Nagah farm, Khatatba village, Menoufia governorate, Egypt in the year 2005, in order to use the ability of rice-straw mulching as cheap farm residue, to reduce the effect of deficit irrigation on highly sensitive crop for water deficit. Split plot design consisted of soil surface covering case (rice straw mulching (500g/m 2 ) and no-mulch) as main plot with four amounts of applied water 70, 80, 90, and 100% of ET c as sub-plot. Cucumber crop was irrigated by drip irrigation system under sandy soil conditions. Using rice straw mulch led to decrease the soil moisture reduction by 66, 57, 48.9, and 38 % compared with nomulch treatments for the 70, 80, 90, and 100% of ET c respectively. All rice straw mulch treatments showed a productivity increase compared to nomulch. The maximum crop yield 8.24 Mg/fed was obtained under rice straw mulching and 100% of ET c percentage causing a 29.6% increase in productivity compared with the crop productivity obtained at the treatment of same amount of applied water under traditional conditions. Rice straw mulch led to increase water use efficiency (WUE) the maximum value of WUE under rice straw mulch was 6.55 kg/m 3 with 90% of ET c while it was 4.37 kg/m 3 under the same conditions with no-mulch. Maximum benefit-cost ratio, 2.92 was obtained under rice straw mulch with 90% while it was 2.86 for nomulch with 100%. The study recommended using rice straw mulch with 90% of ET c to obtain the maximum product of unit of water and maximum economic benefit.
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