|
|
| Bildiri Özetleri | |
| Ana Sayfaya Dönüş |
| ISD Ana Sayfası |
|
Şenay Özden, Kezban Şahin, Sebahattin Keskin Soil and Fertilizer Research Institute ABSTRACT The aims of the study were to validate the applicability of Productivity Index Model, which is acceptable among other models of similar nature in terms of estimating likelihood relationships between erosion and productivity to the widespread soil orders in Ankara and to determine soil loss tolerance on the basis of soil orders by using Productivity Index (PI). Study was carried out at five location in wheat and barley fields. Soil samples were taken from horizons of 35 soil series previously surveyed and mapped as Entisol, Inceptisol and Aridisol were subjected to some physical and chemical analyses. Data obtained from laboratory analyses of each location were entered into the model as data files. Erosion rates were calculated for each series by using TURTEM (Turkey Erosion Estimation Model). By making use of 10 ton/ha/year value, which was erosion rate obtained from the studies of USLE parameters and data accrued from the aforementioned research, three version of PI model were run. In addition, soil loss tolerances were calculated by employing PI values. Three versions of PI model were evaluated on the basis of yield, crop, and soil order. According to the results, version 1, which gave the most significant correlation than others is recommended The fact that a difference between 0.05 - 0.10 was recorded in PI values discloses that erosion has significantly affected the yield and soil conservation practises have to be taken. INTRODUCTION Soil erosion depletes soil productivity, but the relationship between erosion and productivity is not well defined. Until the relationship adequately developed, selecting management strategies to maximize long-term crop production will be impossible (Brown, 1984; Lal, 1993 ). The relationship between soil productivity and soil erosion has participated in important issue of soil science for centuries. Simenson stated that the first model of productivity index was used by Chinese 40 centuries ago (Kiniry at all, 1983). The new approaches have been dealt with recently in order that the changes in soil productivity are determined regarding soil erosion and the models of this approaches have begun to be confirmed by many soil scientist (Wilson, 1991). These new approaches as follows; 1. The Erosion-Productivity Impact Calculator (EPIC) (Williams at all, 1983) 2. The Productivity Index Model (PI) (Kiniry at all, 1983). The principle of PI Model is a function of soil condition because of the fact that productivity is a function the growth of plant root, PI model describes the profile of plant root growth and it connect the relationship the gradual of development with productivity. MATERIAL AND METHODS The Model : The Productivity Index Model provides a relatively simple method to assess the impact of erosion on crop production. For different soil depth, the sum of the multiplication of relative values of five different soil parameters state that soil stratum, which are the issue of being examined, the gradual of convenience for the growth of plant root. The basis of the original model was to define the response of a crop in terms of available water (A); aeration (B); bulk density (C); pH (D) and electrical conductivity (EC). These factors are expressed as sufficiency ratings which range from 0 to 1. The Productivity Index (PI) equation is as follow: PI = SUM1-n(Ai x Bi x Ci x Di x Ei xWFi) Where WF is a weighting factor related to root distribution in each soil layer 'i', and 'n' is the number of soil layers. In Version 1, PI is calculated as the product interaction of available water, transmission porosity, pH and electrical conductivity sufficiencies weighted according to the theoretical root distribution function. In Version 3, PI is calculated as the minimum of transmission porosity, pH and electrical conductivity sufficiencies weighted according to the theoretical root distribution function and then modified by the sufficiency of total plant available water store. In Version 4, PI is calculated as the minimum of available water, transmission porosity, pH and electrical conductivity sufficiencies weighted according to the theoretical root distribution function. The Equation Of Soil Loss Tolerances : PI may be used to estimate quantitative soil loss tolerance levels (Pierce et al., 1984) based on a soil's productivity, its vulnerability to productivity losses from erosion, an allowable reduction in productivity and a planning horizon in years.  DISCUSSIONS Disturbed and undisturbed soil samples taken from the horizons of Entisol, Inceptisol and Aridisol profiles were analysed for the purpose of determining field capacity, wilting point, EC, pH, texture (very fine sand, sand, silt, clay), organic matter. Data obtained from laboratory analyses were entered into the model as data files. Erosion rates were calculated for each series by using TURTEM (Turkey Erosion Estimation Model) (Özden and Özden, 1997). For that purpose, R factor was obtained from published reports, K factors were determined from laboratory analysis by using TURTEM; slope length was considered 100 m and steepness of slope was taken from published reports belonging to series; P factors were assessed according to the tillage method used and C factors were calculated from data on crop management described in terms of average sowing date, harvest date, average yield of grain, and typical timing and operation of tillage or crop residue management practices. PI's three versions were run by using erosion rates of soil series calculated from TURTEM and 10 ton/ha/year (the erosion rate) obtained from experiments pertaining to USLE parameter studies (Doğan ve Küçükçakar, 1996). Three version of PI model were evaluated on the basis of soil orders, crops and yields (Figure1-4). At the same time, soil loss tolerances were calculated by using all the Pl values. Different results were found regarding soil loss tolerance by series. The values varied from 0.9 to 48.8 ton /ha/year and 10 ton/ha/year according to erosion properties of the series and changed between 6.6-15.5 ton/ha/year. In PI1 version, the lowest value for Kule series as 0.0228 and the highest value for Polatlı series as 0.5627 were recorded. After 100 years, Çuğlu series would have the lowest (0.000) value and Çayırlı series would have the highest value (For detail see Table1). In PI3 version the lowest (0.04) value is of Bahçe arkası and the highest value (0.8267) is of Çayırlı series. In PI4 version, the lowest value was obtained in Kule series as 0.026. The highest value for Küçükdağ series (0.6851) was recorded. After 100 years, the same series would have the lowest and the highest values (For detail see Table1).  
 Figure 3. Comparison of PI version's initial values according to the erosion rates derived from TURTEM  Figure 4. Comparison of PI version's initial values according to 10 ton/ha/year (the experimental erosion rate) As to limiting factor for plant root growth, versions has given different results. For example, In PI1 and PI3, the first horizon of Aktaş series (Erosion rate is 10 ton/ha/year) while there is no aeration problem in first 15 years, after 15 year, model has shown that the water will be problem in the future in that horizons and the other horizons will have aeration and water problem, also. In PI4 version for that series the same aeration will be problem for first horizon, after 15 year, there will be no problem in the same horizon. According to 10 ton/ha/year and erosion rate, while evaluating first version of PI, limiting factors have changed in Esenboğa, İşletmealtı, Zir ve İkizce series. It has not changed the limiting factors. In 3.version, Altınova, İşletmealtı, Esenboğa, Yüzükbaşı, Zir, İkizce serieses, some changes was obtained. Limiting factors has changed in 4. Version for Aktaş, Zir ve İkizce series. In general for 1.ve 4 version, water will be problem, in 3. version pH will be problem. According to the results, PI1 version is more accurate than the others. The correlation coefficient between PI1 version was found around r=0.78 in relation to the productivity values of wheat in the different series of Aridisol and the relationship was found to be important in 0.05 levels. The equation is y=1858.4+4985X . The first version which gave the highest correlation among the three versions is recommended. Unlike 4.version which presented similar results to 1.version, 3. versions which also gives different results showed that pH factor in the soils where there is no pH problem was a substantial factor hindering the growth of plant root when evaluating the analysis values of soil in this sense, 3. version wasn't suitable. Differences in PI values were between 0.05-0.10 shows that practices of soil conservation should be taken because of the fact that erosion has considerably effect on productivity. In this sense, PI values of most series which were studied in the execution of project has low PI. Therefore, some management practice must be taken in order to reduce the erosion. SUGGESTIONS - The results of PI model are of importance in terms of taking precuation as to crop and soil management practices against erosion and conserving soil productivity in sustainable agricultural. - Model gives important results that in low erosion rate by years soil productivity will not reduce, and in high erosion rate, loss of soil productivity will increase. - Negative factors affecting plant growth can be prevented by estimating limiting factors. - In soil conservation planning, soil series should be taken in to consideration because of their different characteristics and behaviours. - LS factors should be estimated by GIS techniques. - Different results were found regarding soil loss tolerance by series. It is essential that soil loss tolerance and the other criterions as regards catchment should be taken into account. - The value of soil loss tolerance obtained by model results shows the importance of evaluation in the series base . Tolerance values obtained from PI model is not enough alone to express soil loss tolerance values. Therefore overall watershed characteristics should be taken into accont. REFERENCES Brown L.R. (1984). The global loss of top soil. Journal Of Soil and Water Conservation 39:162-165. Doğan, O. ve Küçükçakar, N. 1996. Ankara yöresinde üniversal toprak kaybı eşitliği parametreleri. Köy Hizmetleri Ankara Araştırma Enstitüsü Yayınları, Genel Yayın No:199, Rapor Seri No:105, Ankara. Kiniry L. N. , Scrivner L.C. & Keener M.E. (1983). A Soil Productivity Index Based Upon Predicted Water Depletion and Root Growth . University of Missouri -Colombia Lal R. (1993). Monitoring Soil Erosion's Impact on Crop Productivity. Soil Erosion Methods. Soil and Water Conservation Society. Özden Ş. & Özden D.M. (1997). Erozyonu Azaltmak Amacıyla Yönetim Metodlarının Seçiminde Yardımcı Olacak Bilgisayar Programının Geliştirilmesi. 1995-1996 Yılı Araştırma raporu. K.H.G.M., T.G.A.E Müdürlüğü yayınları, Genel yayın no:219, Rapor seri no: R-135, Ankara Pierce F.J., Larson W.E., Dowdy R.H. & Graham. W.A.P. (1984). Soil Loss Tolerance: Maintenance of Long -Term Soil Productivity Journal Soil and Water Conservation 39 (1) : 137 Williams J.R., Renard K.G. & Dyke P.T. (1983). EPIC A New Methot For Assesing Erosion's Effect on Soil Productivity. Journal of Soil and Water Conservation. 38 (5) : 381-383 Wilson J.P., Sandor S.P. & Nielsen G.B. (1991). Productivity Index Model Modified to Estimate Variability of Montana Small Grain Yields. Soil Science Soc. Am. J. 55:228-234. |