As the main component of terrestrial energy and water balance, evapotranspiration (ET) moves a large amount of water and energy in the form of latent heat flux from bare soil and vegetated surfaces into the atmosphere. Despite the development of many methods and equations through past decades, accurate ET estimation is still a challenging task, especially for the Red River Valley of the North (RRV) that has limited updated information on ET either for landscape or agricultural water management. The overall objective of first study was to evaluate the ASCE-EWRI reference ET (ETo) method by developing an accurate crop coefficient (Kc) using an eddy covariance (EC) system over an unirrigated turfgrass site. The results showed that with mean ETgrass/ETo ratio as 0.96 for the entire growing seasons of turfgrass, the ASCE-EWRI ETo method is valid for guiding the turfgrass irrigation management in cold climate conditions. In a Controlled drainage with subirrigation (CD+SI) field, an EC system was used to measure and quantify energy flux components along with soil water content (SWC) and water table depth (WTD) measurements during four corn growing. This study showed that the subsurface drainage along with the CD + SI system can be used for optimal water management with an improvement of 26.7% and 6.6% of corn yield during wet and dry year, respectively. For the final task, ET was measured using EC, Bowen ratio system (BREB), and soil water balance (SWB) method during the corn growing season. The comparison of the EC and the BREB system illustrated the advantages of using the residual method to close the energy balance closure of EC. Among the different time approaches for SWB method, ET by the SWB method using the average soil water contents between 24:00 to 2:00 time period showed non-significant differences (alpha = 0.05) compared to the BREB system during the observation periods. / USDA National Institute of Food and Agriculture project / USDA NCR SARE project / ND Soybean Council / ND Water Resources Research Institute / ND Agricultural Experimental Station / USDA Hatch project / NASA ROSES Project

Turfgrass water use (seasonal turfET) and crop coefficients were determined and a mathematical soil-water balance model for non-weighing drainage lysimeters, which simulates the occurrence (timing and amount) of drainage, was developed. Pairs of non-weighing drainage lysimeters were used to determine crop coefficients for turfgrass in four locations in the state of Utah: Logan Golf and Country Club, Murray Golf Course, Brigham Young University (Spanish Fork) Experiment Farm, and Sunbrook Golf Course (St. George). Daily weather data including air temperature, relative humidity, average wind travel, total solar radiation, precipitation, and average soil temperature were collected with an electronic weather station at each site. Daily precipitation was measured in three sites throughout the season: Murray, Spanish Fork, and Sunbrook. At Logan Golf and Country Club, precipitation was measured to November 10,2002. Water use (averages of two lysimeters) during the growing season varied from 684 to 732 mm for three years (2000- 2002) for the mid-April through late-October observation period at Logan Golf Course; 699 mm for May through October at Murray; 469 mm at Spanish Fork; and 896 mm for late-February through early November at Sunbrook, for 2002 growing season. Calculated seasonal Etr using the 82 Kimberly Penman equation with a 1 00-miles-per-day wind travel limit varied from 1166 to 1229 mm at Logan Golf and Country Club, 1067 mm at Murray, 839 mm at Spanish Fork, and 1574 mm at Sunbrook. Seasonal Etr calculated using the PM ASCE std Etr equation was greater than the 82 Kimberly Peru11an . Seasonal Eto calculated using the FAO#56 Eto equation was less than both the 82 Kimberly Penman and the PM ASCE std Etr equations. Calculated crop coefficients (as a ratio of measured crop water use and calculated potential evapotranspiration) based on alfalfa reference evapotranspiration with the 1982 Kimberly-Penman equation averaged 0.58 for the three years at Logan. Seasonal averages varied from 0.57 to 0.60. Seasonal crop coefficients (2002) were 0.57 for Logan, Spanish Fork, and Sunbrook, and 0.65 for Murray. Short-period crop coefficients also varied within a given season. Short-term crop coefficients derived from a time of wetting and drainage experiment averaged 0.55 at Logan, 0.56 at Murray, 0.60 at Spanish Fork, and 0.56 at Sunbrook.

The potential of basin wildrye (Elymus cinereus Scribn. & Merr. 'Magnar') and tall wheatgrass [Agropyron elongatum (Host) Beav. 'Jose '] to establish on saline, arid rangelands in the Great Basin in relation to soil water and salinity was compared in field and laboratory experiments. Tall wheatgrass had higher emergence and establishment on a nonsaline and a saline soil (electrical conductivity of the saturation extract of 7 dS·m-1) over a range of spring precipitation as simulated by sprinkler irrigation. Basin wildrye will require supplemental irrigation to establish on soils of similar salinity. In the absence of precipitation, soil salinity increases and matric and osmotic potentials rapidly decrease as the surface soil dries in late spring. Germination and growth responses in relation to salinity and drought in laboratory experiments were consistent with emergence and establishment results in the field experiments. Tall wheatgrass had higher total germination, rate of germination and radicle growth under decreasing osmotic potentials and higher emergence under decreasing matric potentials than basin wildrye. Tall wheatgrass had greater root and shoot yield than basin wildrye when osmotic potentials in sand cultures were decreased by solutions of NaCl, Na2SO4 and CaCl2.Tall wheatgrass is more tolerant of salt and boron than basin wildrye, but basin wildrye is highly salt tolerant compared to most forage species. Tall wheatgrass had more rapid root elongation and more extensive root growth than basin wildrye seedlings grown in 60-cm soil columns filled with nonsaline and saline soil. Germination and growth of both species was reduced by ions in addition to the effects of water stress due to low osmotic potentials. Rate of germination and radicle growth of both species was less in salts than in isosmotic polyethylene glycol solutions. Seedlings exhibited less growth in saline than nonsaline soil even when plant water stress was minimal or when leaf water potentials were low but turgor was maintained by osmotic adjustment. Germination at low osmotic and matric potentials and root elongation in relation to salinity may be important plant responses to use in evaluating the potential for establishment of new plant materials on saline, arid rangelands.

This study evaluated the effectiveness of chiselling and elemental sulfur fertilization in improving an upland and a swale range site with fine loamy, carbonatic, typic calcixeroll soils in the Ait Rbaa Perimeter of central Morocco. Ponding infiltration, soil water content on a mass basis of the 0- to 10-cm and 10- to 20-cm soil layers, peak season biomass production, and botanical composition were monitored during the two growing seasons following the treatments (1984/85 and 1985/86). Chiselling significantly improved infiltration on both sites, although the improvement was greater on the finer and less stony swale site, where chiselling resulted in more stable ridges. The land treatment also increased the average water content by weight of the 0- to 20-cm soil layer. The increase was more frequent on the upland site and most pronounced on its o- to 10-cm surface soil layer. In the chiselled treatments, average soil water content decreased with soil depth on the upland site while it increased on the swale site because of differential furrow stability and soil texture. Both the average infiltration rates of 5 cm of water and the average water content varied with sampling time, although generally in opposite directions. The application of elemental sulfur at the rates of 0, 30, and 60 kg ha-1 did not significantly affect any of the measured variables. Average peak season biomass production was 11% greater with chiselling. Chiselling also positively affected botanical composition on the upland site by depressing average forb proportion and increasing legume ratio in the first growing season. The gain in biomass does not seem to be high enough to strongly recommend chiselling in the Ait Rbaa Perimeter before performing an economic analysis of the operation.

京都大学 / 0048 / 新制・論文博士 / 博士(農学) / 乙第13181号 / 論農博第2860号 / 新制||農||1061(附属図書館) / 学位論文||H30||N5103(農学部図書室) / (主査)教授 小杉 緑子, 教授 北山 兼弘, 教授 舟川 晋也 / 学位規則第4条第2項該当 / Doctor of Agricultural Science / Kyoto University / DFAM

Soil moisture deficits often hinder rangeland revegetation efforts. Due to sheer numbers and germination timing, invasive annual species can easily outcompete those of desired seeded species for resources, including water. One way to increase seedling establishment may be to increase the amount of water available to seeded species. Superabsorbent polymers (SAPs) can absorb and release hundreds of times their weight in water and slowly release it. Concentrated SAP bands at or near seedling rooting depth may act as a soil water reservoir for germinating seedlings and increase rangeland seedling establishment. The objective of these studies was to evaluate the effect of banded SAP on soil moisture and seedling establishment through a series of eight glasshouse and field trials with different combinations of: species, SAP band rate, SAP band placement depth, seeding rate, fertilizer application, and seedling distance from the SAP band. Two grasses, bottlebrush squirreltail (Elymus elymoides) or Siberian wheatgrass (Agropyron fragile) were used as test species in all studies but one. In that study six species commonly used in rangeland restoration [bottlebrush squirreltail, crested wheatgrass (Agropyron cristatum (L.)), Lewis flax (Linum lewisii Pursh), yellow sweet clover (Melilotus officinalis), Wyoming big sagebrush (Artemisia tridentata Nuttall ssp. wyomingensis Beetle Young), and forage kochia (Kochia prostrata (L.) Schrad.)] were used. Concentrated band of SAP at rates up to 6000 kg ha-1 were placed below the seeds at depths ranging from the soil surface to 15 cm deep or mixed into the top 8 or 15 cm of soil. Measurements varied with trial. Soil moisture measurements included gravimetric water content, volumetric water content, and/or soil matric potential. Seedling growth parameters included seedling time to emerge, number emerged, longevity, percent of seedlings alive, shoot length, blade count, root length, root biomass, shoot biomass, and/or root:shoot ratio. Banded SAP at high rates increased usable soil moisture up to 49 days in the glasshouse and in spring of the first year after installation in the field. Rates ? 1500 kg ha-1 increased seedling longevity up to 12 days in the glasshouse but resulted in raised and cracked soil. This negatively impacted seedling survival in the field but not the glasshouse and may also reduce the amount of available soil moisture over time. Banded SAP at rates < 1500 kg ha-1, intended to reduce soil cracking, had no impact on soil moisture or live seedlings in the field. Further work is needed to investigate alternative application methods, such as blending the SAP into the soil.

Forestry has been found to increase the accumulation of methyl mercury (MeHg), a highly neurotoxic compound, in forest soils. However, little is known about how forestry influences catchment processes that governs the mercury (Hg) methylation process. Logging residues are used in harvested catchments in stick roads to reduce soil disturbances caused by forestry machinery. Logging residues left on site after harvest have been suggested to act as a source of high-quality organic matter that stimulates the activity of the microorganisms that carry out the methylation of Hg. In addition, logging residues might influence the activity and abundance of methylating bacteria by reducing the temperature fluctuations in soils below residues and by increasing the soil moisture content. To evaluate the impact of logging residues on the accumulation of MeHg, an experimental field study was carried out in three sites, one in Uppland and two in Västerbotten. The concentration of MeHg was compared between soils covered with residues and soils without residues, and between the lower and upper parts residue piles. Logging residues were not found to influence the levels of MeHg in soils. However, an increased accumulation of MeHg was found in the lower part of residue piles. The accumulation of MeHg in the lower parts was accompanied by a reduced temperature amplitude and an increased water content compared to the upper part of the piles. The increased formation of MeHg might have been mediated by an increased water content in the lower part of the residue piles, possibly by increasing the abundance and activity of Hgmethylating microorganisms due to suboxic/anoxic conditions within biofilms around decomposing needles. The dissolved organic matter composition in soil water differed in soils below residues compared to without residues, but the organic matter signature in soil water under residues was not found to be compliant with an elevated mercury methylation rate. As MeHg accumulated in the lower part of residue piles could become mobilized and transferred to surface water, the suitability of using logging residues in stick roads depends on the location within the catchment. The removal of logging residues could prevent the potential mobilization of MeHg from residue piles. Though, as soil disturbances may cause an increased Hg methylation rate and mediate MeHg export to surface waters, other form of protection, e.g. logging mats, should be used if logging residues are not used to protect soils. / Mänsklig aktivitet har lett till förhöjda halter av kvicksilver (Hg) i atmosfären. Genom långväga transport och deposition har detta orsakat förhöjda halter i svensk natur. Den huvudsakliga exponeringsvägen av Hg för människan sker genom konsumtion av fisk. Halterna av Hg i svensk insjöfisk överstiger EU:s gränsvärden för god kemisk status samt Världshälsoorganisationens riktlinjer för konsumtion i majoriteten av svenska vatten. Ackumuleringen av Hg i biota sker främst i form av metylkvicksilver (MeHg) som är starkt neurotoxiskt. Avverkning av skog tros bidra till en ökad bildning av MeHg i skogsmark genom att skapa miljöer som gynnar etableringen och aktiviteten av de mikroorganismer som omvandlar icke-organiskt kvicksilver (Hg(II)) till organiskt kvicksilver (MeHg). Dessutom kan skogsbruk bidra till en ökad export av MeHg till följd av ändrade hydrologiska förhållanden samt markskador. En ökad bildning av MeHg är oönskad då mobilisering sedermera kan ske till vattendrag där MeHg kan ackumuleras i akvatisk biota. Dock är kunskapen om hur skogsbruk påverkar specifika processer som är av betydelse för metyleringen av Hg begränsad. Inom skogsbruk används avverkningsrester, bestående av till exempel grenar och toppar, i rishögar för att skydda marken mot körskador. Avverkningsrester som lämnas kvar på området efter avverkning tros bidra till en ökad metylering genom att utgöra en källa av högkvalitativt organiskt material vilket kan stimulera bakteriell aktivitet. Dessutom kan avverkningsrester bidra till en ökad metylering av Hg genom att minska temperaturfluktuationerna i mark täckt med ris samt öka markens vattenhalt, vilket kan bidra till en ökad etablering samt att stimulera aktiviteten av Hg-metylerande mikroorganismer. För att utvärdera effekten av avverkningsrester på ackumuleringen av MeHg genomfördes en experimentell fältstudie där koncentrationen av MeHg jämfördes i mark täckt med ris och mark utan ris. Dessutom undersöktes huruvida en ökad metylering kan ske i den nedre delen av riset, vilket skulle kunna möjliggöras av bakterier i biofilmer kring ris under nedbrytning. Koncentrationen MeHg var högre i den nedre delen av rishögarna jämfört med den övre delen. I den nedre delen av riset var temperaturfluktuationerna lägre och vattenhalten högre än i den övre delen av riset. Ackumuleringen av MeHg kan ha skett via biofilmer i de nedre delarna av riset, där tillgången till hög kvalitativt organiskt material samt mer syrefria förhållanden kan ha gynnat etableringen och aktiviteten av de bakterier som utför metyleringen av Hg. Däremot hade typen av marktäcke, dvs mark täckt med ris och mark utan ris, inte någon påverkan på metyleringen av Hg. Karaktären av organiskt material i markvatten skiljde sig mellan typ av marktäcke, men visar inte på att avverkningsrester utgör en källa av högkvalitativt organiskt material. Vattenhalten i mark under rishögar skiljde sig inte jämfört med mark utan ris, men temperaturen var lägre med mindre variation i mark under rishögar. Därmed visar resultatet på att avverkningsrester kan bidra till en ökad bildning av MeHg. En potentiell mobilisering av MeHg som bildats i rishögarna skulle därför kunna bidra till en ökad export av MeHg från avverkade områden. Användningen av avverkningsrester, för att skydda marken vid körning med skogsmaskiner, anses ändå vara fördelaktig för att minimera utläckage av MeHg. Körskador kan skapa stående vattensamlingar där MeHg kan bildas samt kompaktera mark och skapa snabba ytliga flödesvägar i området. Däremot tyder resultatet på att användningen bör ske med hänsyn till att förhindra eventuell transport av MeHg till vattendrag. Ifall avverkningsrester inte används för att motverka markskador bör ett substitut användas, exempelvis stock-mattor, då körskador kan bidra till en ökad metylering och mobilisering av MeHg. Dock saknas kunskap om eventuell mobilisering av MeHg från rishögar till vattendrag och detta bör utvärderas i framtida studier.

Nine provenances of Turkish red pine (<i>Pinus brutia Ten</i>.), an eastern Mediterranean conifer, taken from a wide range of locations in Turkey, were grown in individual pots in a greenhouse either with or without joint goose goatgrass (<i>Aegilops cylindrica</i> L.) under either high or low soil water availability for two growing seasons. The study consisted of two separate experiments started at times with varying microenvironmental conditions and Turkish red pine (TRP) provenances. Diameter and secondary needle, stem, and root biomass were measured at the end of the second growing season, while height was measured after both the first and second growing seasons. Pine stem water potential (SWP), measured at the end of the second growing season, was the only physiological variable in the study. / Master of Science

The importance of applying unsaturated soil mechanics concepts to geotechnical engineering design has been widely recognized. Soil water characteristic curve (SWCC) and hydraulic conductivity function (HCF) are vital soil properties that govern engineering behavior of unsaturated soils. In this study, a transient water release and imbibitions method (TRIM) is used to measure the SWCC and HCF under drying and wetting states, which accommodates integrated experimental and modeling techniques. The results of saturated hydraulic conductivity tests through flexible wall method are then used as input parameters for simulating experimental data. In general, the model provides a satisfactory fit to experimental data. Soil water characteristic curves (SWCCs) and hydraulic conductivity functions (HCFs) are presented for a variety of soils that were prepared at different molding water contents and compactive efforts. The influences of dry density, molding water content, and hysteresis have been investigated. Dry density affects soil-water characteristic in terms of its air-entry value (AEV), rate of drying, and size of the hysteresis loop. The test results indicate that the SWCC and HCF obtained in terms of volumetric water content is more sensitive to the changes in dry density than molding water content. Based on cohesive soil results, some statistical relations are proposed to estimate wetting-path SWCC and HCF parameters from more easily measured drying curves. Changes in the van Genuchten's fitting parameters and residual volumetric water content are investigated for both drying and wetting conditions, with changes in the kaolin clay content. / Master of Science / Traditional soil mechanics practice has experienced considerable changes during the past few decades. Within that period, the necessity of unsaturated soil mechanics has gradually emerged and become a part of geotechnical engineering practice. Soil water characteristic curve (SWCC) and hydraulic conductivity function (HCF) are very important properties in the assessment of unsaturated soil behaviors. A transient water release and imbibitions method (TRIM) is used to investigate unsaturated soil properties of a variety of test soils under laboratory conditions. TRIM integrates a testing program and a modeling technique to measure SWCC and HCF concurrently for both drying (water release upon matric suction increase) and wetting (water imbibition upon matric suction decrease) conditions. Compaction, which is a classical application involving unsaturated soil, has the preferred practice for improving the mechanical and hydraulic properties of a soil. The structure and fabric of compacted material is very dependent on the compacted conditions, including compactive effort and molding water content. This paper evaluates the influence of such mentioned factors on the SWCC and HCF. The test results indicate that the SWCC and HCF obtained in terms of volumetric water content is more sensitive to the changes in compactive effort than molding water content. Hysteresis phenomena, the difference in the relationship between the water content of the soil and the corresponding water potential under drying and wetting path, is investigated. Based on cohesive soil results, some statistical relations are proposed to estimate wetting-path SWCC and HCF parameters from more easily measured drying curves.

Thesis (MScAgric)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: The aim of this study was to investigate the influence of crop rotation and soil tillage on the soil water balance and water use efficiency of wheat, canola, lupin and medics in the Swartland sub region of the Western Cape. This trail was conducted as a component study within a long-term crop rotation/tillage trial during 2012 and 2013 at the Langgewens Research Farm (33016’42.33” S; 18042’11.62” E; 191m) of the Western Cape Department of Agriculture near Moorreesburg. The experiment was laid out as a randomized complete block, with a split-plot treatment design and replicated four times. Three crop rotation systems, continues wheat (WWWW), wheat/medic/wheat/medic (WMcWMc) and wheat/canola/wheat/lupin (WCWL) were allocated to main plots. . Each main plot was subdivided into four sub-plots allocated to four tillage treatments namely: zero-till (soil left undisturbed and planted with zero-till planter), no-till (soil left undisturbed until planting and then planted with a tined no-till planter), minimum-till (soil scarified March/April and then planted with a no-till planter) and conventional tillage (soil scarified late March/early April, then ploughed and planted with a no-till planter). All straw, chaff and stubble remained on the soil surface and no-grazing was allowed on all tillage treatments. Three replicates were included in this current study. Only the no-till (NT) and conventional till (CT) were included in this current study as main tillage treatments. The volumetric soil water content was monitored at weekly intervals during the active growing season (May-October) and once a month during the fallow period (November-April) using a Diviner 2000 soil moisture meter. The Diviner 2000 was used to record the soil water content at every 100 mm depth increment up to the maximum depth of the profile. At the end of the growing season the total biomass, grain yield and quality parameters were determined. The soil water balance data calculated from the 2012 season were found to be inconclusive due to too shallow installation of soil water monitoring tubes and big variations in the depth complicating any attempt in comparing data from treatments and cropping systems. Soil water monitoring tubes was installed to a depth of 900 mm in the 2013 season. Complications during planting in the 2013 season resulted in very poor emergence in the CT sites. Weed counts revealed that only 38 % of CT sites were covered by crop, 31 % with weeds and 31 % were completely bare. The NT sites had 40 % crop coverage, 50.5 % grass weed coverage and only 9.5% bare surface. As a consequences crop rotation had no effect on the soil water balance, while the tillage treatments showed a response. The effect that tillage had on the soil water balance was clearly shown in the 2013 season, in which 79 mm more rainfall occurred than the long-term average. NT retained more soil water in the profile in the drier first half of the season when only 30 % of the total rainfall in the 2013 season occurred. There was no real difference in the soil water retention in the second half of the season where 70 % of the total rainfall in the 2013 season occurred. Crop rotation did have a positive effect on grain yield. Wheat monoculture was out performed by legume based cropping systems. This trend was also observed in the biomass production. No significant difference between tillage treatments were recorded when comparing grain yield data. However wheat mono culture was again out-performed by the McWMcW, CWLW and LWCW systems producing on average significantly higher biomass. The data from both seasons suggest that in seasons where more rainfall than the long term average occurs, there is no difference in the RUE between cropping systems or tillage practices.. This study highlighted the major effect that the prevailing weather conditions have and that the expected advantages associated with NT most likely only come into play in dry conditions when plant water availability is limited. / AFRIKAANSE OPSOMMING: Die doel van hierdie studie was om die invloed van grondbewerking en gewasproduksiestelsels op die grondwaterbalans en doeltreffendheid van watergebruik te ondersoek in die koringproduserende gebied van Malmesbury. Hierdie eksperiment is uitgevoer as 'n komponentstudie binne 'n langtermyn grondbewerking/gewasrotasieproef gedurende 2012 en 2013 op die Langgewens Navorsingsplaas (33016'42 .33 'S; 18042'11 0,62' E, 191m) van die Wes-Kaapse Departement van Landbou naby Moorreesburg. Die eksperiment is uitgelê as 'n volledige ewekansige blok, met 'n gesplete perseel behandelingsontwerp met vier herhalings. Drie gewasproduksiestelsels naamlik, koring monokultuur (WWWW), koring/medic/koring/medic (WMcWMc) en koring/canola/ koring/lupiene (WKWL) is elk toegeken aan persele en vier keer herhaal. Elke hoofperseel is onderverdeel in vier subpersele en bewerkingsbehandelings is soos volg toegeken: Konvensionele bewerking (CT) - grond gebreek in Maart/April, en daarna geploeg en geplant met geen bewerkingsplanter. Minimum bewerking (MT) - grond gebreek in Maart/April en daarna geplant met 'n geen bewerkingsplanter. Geen bewerking (NT) - grond is heeltemal onversteur gelaat tot planttyd en daarna geplant met 'n geen bewerkingsplanter. Zero bewerking (ZT) - grond tot planttyd met rus gelaat en dan geplant met 'n sterwielplanter. Alle strooi, kaf en stoppels het op die grondoppervlak gebly en geen beweiding is toegelaat nie. Slegs drie herhalings is ingesluit in die huidige studie en slegs die geen bewerking (NT) en konvensionele bewerking (CT) is in die huidige studie as hoof bewerkingbehandelings ingesluit. Die volumetriese grondwaterinhoud is weekliks gemonitor tydens die aktiewe groeiseisoen (Mei - Oktober) en een keer 'n maand gedurende die braaktydperk (November - April) met behulp van 'n Diviner 2000 grondvogmeter. Die Diviner 2000 is gebruik om die grondwaterinhoud by elke 100 mm diepte tot die maksimum diepte van die profiel te bepaal. Aan die einde van die seisoen is die totale biomassa, graanopbrengs en kwaliteitparameters bepaal. Die data vir grondwaterbalans van die 2012-seisoen is buite rekening gelaat weens te vlak installering van moniteringsbuise en groot variasie in die dieptelesings wat enige poging om vergelykende data van rotasie en behandelings te verkry, bemoeilik het. Moniteringsbuise vir grondwater is geïnstalleer tot op 'n diepte van 900 mm in die 2013-seisoen. Komplikasies tydens die plantaksie in die 2013-seisoen het gelei tot 'n baie swak opkoms in die CT-persele. Slegs 38 % van die CT-persele was bedek deur die gewas en 31 % met onkruid, terwyl 31 % van die oppervlak onder CT-behandeling heeltemal kaal was. Die NT-persele het 40 % gewasbedekking, 50.5 % grasbedekking en slegs 9.5 % kaal oppervlak gehad. Dit het die poging, om die effek van wisselboustelsels op die grondwaterbalans, in die wiele gery. Alhoewel wisselbou skynbaar geen effek op die grondwaterbalans gehad het nie, het die tipe bewerking egter wel ‘n effek gehad. Die effek van grondbewerking op die grondwaterbalans het duidelik na vore gekom in die 2013-seisoen. In hierdie seisoen het 79 mm meer reën geval as die langtermyngemiddelde. Geen bewerking het meer grondwater in die droër eerste helfte van die seisoen in die profiel behou, toe slegs 30% van die totale reënval in die 2013 geval het. Daar was geen beduidende verskil in die grondwaterretensie in die tweede helfte van die seisoen toe 70% van die totale reënval in die 2013 geval het nie. Wisselbou het egter 'n positiewe uitwerking op die graanopbrengs gehad. Koring monokultuur is in opbrengsyfers geklop deur stelsels met peulplante as komponent. Hierdie tendens is ook waargeneem in die biomassaproduksie. Bewerkingsbehandelings het geen beduidende verskil in graanopbrengste tot gevolg gehad nie, hoewel die biomassaproduksie van koring monokultuur weer geklop is deur die McWMcW-, CWLW- en LWCW-stelsels. Die data van beide seisoene dui daarop dat in seisoene waar meer reën as die langtermyn gemiddelde voorkom, daar geen verskil in die RUE tussen verbouingstelsels of bewerkingspraktykes was nie. Hierdie studie beklemtoon die groot invloed wat die heersende klimaat speel en dat die verwagte voordele wat verband hou met NT waarskynlik slegs ‘n rol speel in droër jare.