Response of maize to rainwater harvesting and conservation techniques on the Glen/Oakleaf ecotope

[摘要] English: Rainfall in semi-arid areas fluctuates constantly and it is difficult for farmers to increase crop productivity. The rainfall is insufficient, erratic and unreliable, which is associated with poor water availability due to increased water losses such as high evaporation from the soil (Es) due to rising temperatures, runoff (R) and deep drainage (D). These unproductive losses (Es, R & D) contribute to inefficient rainfall, which increases food insecurity and poverty. Crops produced in semi-arid areas under rainfed agriculture by smallholder farmers are usually produced using conventional tillage (CON). This system uses a moldboard plough, which turns and exposes the soil and therefore increases Es and R while organic matter is decreasing. In many semi-arid areas, research was conducted to improve crop production.One of these researches was conducted in South Africa at the Thaba Nchu villages where the Agricultural Research Council (ARC-ISCW) introduced an In-field rainwater harvestingtechnique (IRWH) to increase efficiency and use of limited water. This system was used toreduce unproductive water losses especially Es and R, to optimize rainwater productivity(RWP). This study was conducted to investigate the ability of different rainwater harvestingand conservation (RWH&C) techniques to produce higher yield in using and storing waterefficiently under rainfed conditions of Glen/Oakleaf ecotope.To test the hypothesis, a field experiment was conducted in a semi-arid area under rainfedconditions at the Glen/Oakleaf ecotope in Bloemfontein. The area is characterized by anaverage long-term (LT) rainfall in the growing period of 262 mm and an evaporation demand of 758 mm. Treatments used were In-field rainwater harvesting with a 2.0 m runoff strip (IRWH-2.0m), In-field rainwater harvesting with a 2.4 m runoff strip (IRWH-2.4m), Mechanised basins (MB), Minimal tillage (MIN), Darling plough (DAL) and Conventional tillage (CON). The experiment was conducted in two consecutive growing seasons (2008/09 & 2009/10) laid out in a complete block design (RCBD), with four replications and six treatments. The study was aimed to identify the most appropriate RWH&C techniques that will increase rainwater availability throughout the growing season to increase crop productivity by maximizing yield per unit of water.The first season had 260 mm of rainfall, and was considered a dry season, the second season was a wetter season with 486 mm. rainfall. During the first growing season rainfall was 8% lower than the LT (262 mm), while in the second season it could be considered wetter as the rainfall was 85% higher than LT. Rainfall during Vp was greater than LT during both seasonswith 19% and 49% higher rainfall respectively. During the first dry season rainfall at Rp was41% lower than LT and 160% higher during the second wet season. A short growing maizecultivar was chosen as a crop indicator, PAN 6Q-521R with a growing period of 120 daysfrom planting to harvest.The ecotope had a fine sandy loam soil with a depth of ± 1200 mm and a clay content of15% in the A horizon and 30% in the B horizon. Land preparation was done by loosening up the soil to avoid compaction before implementing the different RWH&C techniques andCON treatment. Therefore, CON treatment was tilled with a moldboard plough. Only CONwas ploughed during the second season and other treatments were not implemented.Evapotranspiration was calculated by using the soil water balance equation for dryland crop production. Soil water content was measured with a neutron water meter and crop water efficiencies (RSE, WUE, PUE & RWP) were calculated. Maize height, stem diameter, leaf area index and biomass were measured in four growth development stages only during the 2008/09 growing season while grain yield was measured during both seasons.The first objective is explained in chapter 4, which was to evaluate soil water balance anddifferent rainwater efficiency (Rainwater storage efficiency (RSE), Water use efficiency(WUE) and Precipitation use efficiency (PUE)) of various RWH&C techniques against CONtillage for possible adoption by smallholder farmers to increase crop productivity. The Plantavailable water at planting, tasseling and harvest were higher with RWH&C techniquescompared to the CON treatment during both growing seasons. Similarly soil water contentduring both seasons were higher with RWH&C techniques compared to CON tillage.However, during the first growing season at 13 DAP, the soil water content of all treatmentswas above the DUL line of 280 mm indicating that D could have occurred. MIN treatmentwas shown to have the highest runoff percentage followed by CON tillage. The ET ofRWH&C techniques during the dry season (2008/09) was higher than that of CON tillage,however more water was lost through Es with RWH&C techniques. During the secondseason RWH&C techniques excluding MIN tillage had higher ET compared to CON tillageand higher Es. RSE was not included during the first season due to late implementation oftreatments. During the second season IRWH-2.0 m and IRWH-2.4 m treatments had thelowest RSE compared to MIN CON, MB and DAL treatments. The results showed thatIRWH-2.0m treatment had the lowest WUEET during both seasons. During the dry season (2008/09) WUEEV based on transpiration was highest on the IRWH-2.0m treatment andduring the wetter season (2009/10) CON treatment had the highest WUEEV. During the2009/10 season, RWH&C techniques excluding IRWH-2.0m showed to have greater PUEfg than that of CON treatment. During the dry season the results showed a higher PUEg with RWH&C techniques than that on CON treatment; however during the wet season PUEg was higher with IRWH-2.4m treatment compared to that of CON treatment. For both seasons (2008/09 & 2009/10) IRWH-2.4m, MIN and MB techniques had greater RWP compared to CON tillage. Overall the results showed that RWH&C techniques collected and stored water better during the dry season than in the wet season.The second objective of this study was to determine maize performance under the variousRWH&C techniques compared to CON tillage on the Glen/Oakleaf ecotope. This objective is explained in Chapter 5. Plant height, stem diameter and LAI data were collected only during the first season and the study revealed that maize plants exposed to the CON treatment were taller and thicker compared to RWH&C techniques. During the Vp, plants exposed to the CON treatment had lower LAI than those exposed to RWH&C techniques. At 66 DAP there were no differences between the treatments, however, at 90 DAP plants exposed to the CON treatment had higher LAI. During the Vp of the first season at 30 DAP, plants exposed to the IRWH-2.4m treatment had greater biomass than all other treatments, however during the second season plant biomass exposed to the IRWH-2.0m, and MB treatments were greater than those exposed to the CON treatment. During the first season at 45 DAP plants biomass exposed to the MIN and IRWH-2.0m treatments were both greater than that of other treatments and during the second season plants exposed to the CON treatment were higher than those exposed to the RWH&C techniques. During the Rp at 66 DAP, in both seasons plants exposed to the DAL treatment produced less biomass than in all the other treatments.During the 2008/09 season at 90 DAP, plants exposed to the IRWH-2.4m, MIN and CONtreatments were higher than DAL. However, in the second season at 90 DAP plants showed no difference in biomass between treatments. Grain yield differed between the two seasons due to differences in rainfall. During the dry season of 2008/09, RWH&C techniques had higher grain yield than that of CON treatment. In the wet season of 2009/10 IRWH-2.4m was the only RWH&C technique with a high yield. It was concluded that RWH&C techniques were most likely to perform better in dry conditions than during wetter conditions. During the wet season only IRWH-2.4m techniques performed better than that of CON treatments.

[发布机构] University of the Free State