Evaluating maize production potential of selected semi-arid ecotopes using a water balance model

["Corn -- South Africa -- Glen","Water balance (Hydrology) -- Measurement","Dissertation (M.Sc.Agric. (Soil, Crop and Climate Sciences))--University of the Free State, 2003"]

Bairai Zere, Teclemariam ; ["Van Huyssteen, C. A.","Hensley, M."]

University of the Free State

Others  :  http://scholar.ufs.ac.za/xmlui/bitstream/11660/6152/1/ZereTB.pdf

瑞士|英语

来源: University of Iowa

【 摘 要 】

English: The quantitative evaluation of crop production potential is important for sustainable and wiseland use as well as for food security where subsistence farmers are involved. It is ofparticular importance in arid and semi-arid areas where rainfall is marginal and variable. Thisstudy aims at making a quantitative evaluation of the maize production potential of theGlen/Hutton and Glen/Oakleaf ecotopes which are located at the Glen Agricultural ResearchStation in the semi-arid Free State Province of South Africa. The objective was tocharacterize the ecotopes, and to make long-term yield predictions with a yield predictionmodel using long-term climate data.A detailed profile description, soil analyses and an in situ drainage curve were made for theGlen/Oakleaf ecotope. Similar data for the Glen/Hutton ecotope was obtained from previousresearch work (Hensley et al., 1993; Hattingh, 1993; Hensley, personal communication,2002). A neutron water meter (NWM) was calibrated for each horizon of the Oakleaf soil onthe Glen/Oakleaf ecootpe. The plant available water (PAW), defined as the differencesbetween the drained upper limit (DUL) and the lower limit (LL), for maize grown on theGlen/Hutton and Glen/Oakleaf ecotopes was 133 mm and 120 mm respectively. Consideringa mature maize crop growing in summer on these two ecotopes, PAW can be defined as thedifference between the crop modified upper limit (CMUL) and LL. Results for this parameterwere 183 mm and 192 mm for the Glen/Hutton and Glen/Oakleaf ecotopes respectively. Thereason for the relatively high value of the latter is its slower drainage rate, which enables thecrop to extract more water while drainage proceeds between field saturation and DUL than inthe rapidly draining Hutton soil. Yields measured on experiments on the two ecotopes for 12seasons on the Glen/Hutton and 10 seasons on the Glen/Oakleaf ecotope indicate that thesetwo ecotopes have similar production potentials.For the development of a yield prediction model it was necessary to find a way to estimatedaily crop evapotranspiration (ET). Based on the semi-arid climate, soil morphologicalobservations and results of soil analyses, deep drainage from these two maize ecotopes wasconsidered to be negligible. Equations for predicting runoff from rainfall (P) were developedbased on long-term runoff measurements made at nearby sites (Du Plessis and Mostert, 1965;Hensley, personal communication, 2002). Because of fairly good r² values (0.84 and 0.82)the equations can be considered as reliable enough for the purpose of this study. A procedurefor estimating soil water content at planting, from the rainfall pattern during preceding fallowperiod and grain yield in the preceding season, was also developed based on measurements from previous research work (De Jager and Hensley, 1988; Hattingh, 1993). Using all thisinformation it was possible to make a fairly reliable estimation of daily ET.Climate data was used to calculate daily potential evaporation (Eo) values. This enabled thedegree of crop water stress to be defined as ET/Eo , on a daily basis. The maize growing seasonwas divided into three stages i.e. the vegetative, flowering and seed filling stages. A stressindex (SI), defined as the average ET/Eo value for each period, was then calculated. To developan integrated stress index (ISI) for the growing season eight different methods of integratingthe three SI values were formulated. Measured maize yields from experimental plots on thetwo ecotopes were available for 22 seasons (De Wet and Engelbrecht, 1962; De Bruyn, 1974;De Jager and Hensley, 1988; Hattingh, 1993). Integrated stress index values were thencalculated for these seasons and correlated with the biomass yields. This made it possible tochoose the best method of calculating the ISI value from the individual SI's. The ISI with thebest correlation (r² = 0.69) was the one with formula ISI = (2A + 3B + 2C)/7, where A, B andC are the SI values of the three growth periods respectively. The equation to predict totalbiomass (Yb) is Yb = 15238 ISI + 1067 kg ha¹.The biomass prediction equation was used to generate maize yields for 80 seasons (1922/23 -2001/02). Yb was converted to grain yield using a harvest index regression equation based on38 yields from Glen for which both total biomass and grain yield had been measured. Fourproduction techniques were compared, i.e., November planting with conventional tillage(CTN), January planting with conventional tillage (CTJ), November planting with in-fieldwater harvesting and basin tillage (WHBN), and January planting with water harvesting andbasin tillage (WHBJ). Cumulative probability functions (CPF's) of yields were computed forthe four different production techniques. The CPF's indicated that the long-term mean yields(at 50% probability) were 2653, 2 685, 3 108, and 3 355 kg ha¹ for CTN, CTJ, WHBN andWHBJ respectively. The CPF's were compared using the stochastic dominance and theKolmogorov-Smimov (K-S) tests (Anderson et al., 1977; Steel et al., 1997). Stochasticdominance results indicated that the WHBJ and WHBN production techniques have welldefined first degree stochastic dominance over the CTN and CTJ techniques. Januaryplanting showed only second degree stochastic dominance over November planting. The K-Stest indicated that the CPF's of the water harvesting techniques were significantly differentfrom those of the conventional production techniques. No statistical significant differencewas observed with the K-S test between the November and January plantings.