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20 Pags.- 2 Tabls.- 8 Figs. The definitive version is available at: http://ascelibrary.org/journal/jidedh ; This work presents and applies a new methodology to find the optimal topography of a surface irrigation field, achieving a theoretically uniform surface irrigation. For any variant on surface irrigation (basin, border or furrow, with open or blocked end), the method's result is a particular curved topographical shape of a field. This shape distributes water evenly over the field so that distribution uniformity is theoretically 100% and deep percolation disappears. The methodology was applied to two theoretical cases: (1) a one-dimensional blocked-end field, and (2) a two-dimensional square field with corner inflow. For each case, the methodology reached a particular topography in which distribution uniformity was near 100%. To put this methodology into practice, the optimized topography (which has a curved shape) can be fitted with two or more different slopes. An example is shown in which a real field was laser-levelled with two consecutive slopes to fit the optimized topography; it previously was calculated with the methodology presented in this paper. The irrigation was evaluated before and after the optimization. The results indicated an increase of distribution uniformity from 82 to 96%. The topographic optimization methodology offers new information about topography influence on irrigation performance indicators. The main practical conclusion is that this method can be useful to determine the best slope, set of slopes or curved shape when levelling any field for surface irrigation. ; This work was supported by the Government of Arag ´on (Spain) and the European Social Fund (European Union). ; Peer reviewed

19 Pags. The definitive version, with 2 Tabls. and 6 Figs., is available at: http://onlinelibrary.wiley.com/journal/10.1002/(ISSN)1099-1085 ; The correct use of the tension disc infiltrometer requires the membrane of the disc base to be completely in contact with the soil surface. To achieve this contact, a thick layer of sand is commonly placed between the soil surface and the disc base. This paper presents an alternative disc (MDB), which, by incorporating a malleable membrane, allows direct infiltration measurements without using a contact sand layer. Infiltration curves obtained with this new design in a soil under three different tillage management treatments were compared with the corresponding curves obtained with a conventional disc (CDB) that uses a contact sand layer. The cumulative infiltration curves measured with CDB were analysed by the differentiated linearization (DL) method, and the corresponding curves obtained with MDB were analysed using both the DL and the cumulative linearization (CL) models. The values of hydraulic conductivity (K0) and sorptivity (S0) estimated with CDB were also compared with those obtained with MDB. Finally, the cumulative infiltration curves measured with CDB and MDB were compared with the corresponding modelled function for the respective K0 and S0 values calculated with the CL and DL models. The results show that, compared with CDB without a contact sand layer, MDB allows complete soil surface wetting even when non-smoothed soil surfaces are used. The CDB, which yielded average K0 values 18% lower than those estimated with MDB, gave the highest values of standard error for the hydraulic parameters calculated. Furthermore, the subjective method employed in the CDB-DL technique, which requires the first points of the differential infiltration line corresponding to the sand layer to be manually removed, introduces additional uncertainties in estimating S0 and K0. Comparison between the modelled and measured infiltration curves demonstrates that the DL or CL methods applied to MDB gave excellent estimates of S0 and K0. ; This research was supported by the Ministerio de Ciencia e Innovación of Spain (grant AGL2010-22050-C03-02) and by the Aragón regional government and La Caixa (grant GA-LC020/2010). ; Peer reviewed