O conhecimento sobre o balanço de água no solo é essencial ao manejo do sistema solo-água- planta. Esta pesquisa objetivou estudar os componentes do balaço de água em Cambissolo cultivado com meloeiro irrigado por gotejamento, com e sem cobertura da superfície, em Baraúna-RN. Em área experimental de 20 m x 50 m cultivou-se melão Amarelo, variedade AF- 646, no espaçamento de 2,00 m x 0,35 m, num total de dez linhas de plantas de 50 m de extensão cada. A 1/3 e 2/3 da extensão de cada linha de plantas foram instalados quatro tensiômetros, um em cada uma das profundidades 0,1; 0,2; 0,3 e 0,4 m. A instalação foi feita adjacente à linha de irrigação (0,1 m da linha de plantas) entre duas plantas selecionadas, com os tensiômetros espaçados 0,1 m entre si. Em cinco linhas aleatórias fez-se a cobertura com folhas secas de bananeira (Musa sp.) ao longo da linha de gotejamento numa faixa de 0,5 m. Nas outras cinco manteve-se o cultivo sem cobertura. Assim, o experimento consistiu de dois tratamentos, com dez repetições, em quatro períodos fenológicos: inicial (7-22 DAS dias após a semeadura), vegetativo (22-40 DAS), frutificação (40-58 DAS) e maturação (58-70 DAS). As precipitações pluviais foram medidas com pluviômetro e as armazenagens de água estimadas pelo método do trapézio, a partir das leituras dos tensiômetros e das curvas de retenção. Para a determinação das densidades de fluxo de água no limite inferior do volume de controle de solo (0,3 m), foram considerados os tensiômetros nas profundidades 0,2; 0,3 e 0,4 m, sendo que o tensiômetro a 0,3 m foi utilizado para estimar o conteúdo de água no solo, com uso da curva de retenção de água para esta profundidade, e os outros dois para o cálculo do gradiente de potencial total. As densidades de fluxo foram calculadas pela equação de Darcy-Buckingham, com a condutividade hidráulica do solo determinada pelo método do perfil instantâneo. O deflúvio superficial foi desconsiderado e a evapotranspiração real da cultura foi calculada pela equação do balanço de massas. Concluiu-se que: a) à 0,2 m de profundidade a condutividade hidráulica do solo foi baixa; b) o manejo da irrigação com tensiômetros permitiu redução de 45% na lâmina de água em relação à usualmente praticada na região, sem afetar a produtividade da cultura; c) houve efeito positivo da cobertura do solo sobre a armazenagem de água, especialmente nos estádios inicial e vegetativo da cultura; d) o método do balanço de água no solo mostrou-se eficiente na estimativa da evapotranspiração real, em condições de cultivo de meloeiro irrigado; e) a aplicação de uma única lâmina diária de irrigação, mesmo em curto intervalo de tempo, apresenta risco de perda de água por drenagem interna, especialmente nas fases inicial e vegetativa do meloeiro; f) a variabilidade espacial da densidade de fluxo foi elevada quando houve ocorrência de precipitação pluvial; g) não houve efeito da cobertura do solo na evapotranspiração da cultura, nem sobre a produtividade e características pós-colheita dos frutos; h) a curva de coeficiente de cultivo apresenta grandes limitações quando utilizada para fornecer água para o meloeiro. / The knowledge about the soil water balance is essential to soil-water-plant system management. Thus, this research aimed to study the water balance components in an Inceptsol cropped with muskmelon under drip irrigation, with and without surface covering, in the county of Baraúna, Rio Grande do Norte State, Brazil (05º04\'48 S, 37º37\'00 W). In an experimental area of 20 m x 50 m grew up AF-646 muskmelon, spaced 2.00 m x 0.35 m, in a total of ten plants lines 50 m long each. At 1/3 and 2/3 of the length of each plant line, four tensiometers were installed, one in each depths of 0.1, 0.2, 0.3 and 0.4 m. The installation was made adjacent to the irrigation line (0.1 m from the plant line) between two selected plants 0.1 m apart. In five random lines, it was made a covering with dry leaves of banana (Musa sp.) along the drip line in the range of 0.5 m. In the other five there was no covering. Thus, the experiment consisted of two treatments whith ten repetitions in four phenological stages: initial (7-22 DAS - days after sowing), growing (22-40 DAS), fruiting (40-58 DAS) and maturing (58-70 DAS). Rainfall was measured with rain gauge and water storage estimated by trapezoidal method, from tensiometer readings and retention curves. To determine the soil water flux densities at the soil depth 0.3 m, tensiometers at depths 0.2, 0.3 and 0.4 m were considered; the tensiometer at 0.3 m was used to estimate the soil water content, from the soil water retention curve at this depth, and the other two to calculate the soil water total potential gradient. The flux densities were calculated by the Darcy-Buckingham equation, with the hydraulic conductivity being determined by the instantaneous profile method. There was no runoff and the crop actual evapotranspiration was calculated by the mass balance equation. It could be concluded that: a) at 0.2 m soil depth the hydraulic conductivity was low; b) controlled irrigation with tensiometers allowed a reduction of 45% in water application in relation to commonly used practice in the region, without crop productivity change; c) there was positive effect of soil covering on water storage, especially at the initial and vegetative stages; d) the method of soil water balance was efficient to estimate actual evapotranspiration, under irrigated muskmelon conditions; e) the application of a single irrigation depth daily, even in a short time period, presents risk of water to be lost by internal drainage, especially at initial and vegetative muskmelon stages; f) the spatial variability of soil water flux density was high when rainfall incidence occurred; g) there was no effect of covering on crop actual evapotranspiration, neither on yield and post-harvest fruits characteristics; h) the crop coefficient curve has severe limitations when used to provide water to the muskmelon.

Conselho Nacional de Desenvolvimento Científico e Tecnológico / In order to overcome periods of drought and low water availability, deficit irrigation becomes an important tool as long as it is applied on the least sensitive periods of the crops development to reduce the impacts on the productivity. Furthermore, deficit irrigation can be most efficient when there is an understanding of the way plants lose water. Crop evapotranspiration (ETc) is divided into soil evaporation (Es) and crop transpiration (Tc). The objectives of this paper were, beside measuring the soil water balance for different crops (bean, soybean and maize), was to determine adequate crop base coefficients (Kcb) for southern Brazil conditions, partition ETc into Es and Tc to better evaluate and understand soil water dynamics along the crops development cycle, determine water productivity (WP) considering different levels of deficit irrigation, to compare scenarios of water consumption on main and secondary crop schedules. The soil water balance model SIMDualKc was used, after due calibration and validation, using the dual crop coefficient methodology (Kc dual). A series of experiments were done (drybeans in 2010/11; maize in secondary schedule in 2010/11; maize in 2011/12; and soybean in 2014/15), with the imposition of different irrigation deficits as treatments, using drip irrigation and mulching. The results of SIMDualKc simulations show good agreement between the observed and simulated available soil water (ASW) content, values of regression coefficients (b0) were in average 0,98 for drybeans, 0,97 for soybean, 1,0 for secondary schedule maize and 1,05 for regular maize. The adjusted Kcb values for local conditions were respectively to bean, soybean and maize, 0,15; 0,15; 0,2 for the initial period (Kcb ini), 1,03; 1,0; 1,12 for the middle season (Kcb mid); and 0,2 for the end season for all crops (Kcb end). The results of water balance for each crop show that the less water is given to the plants, the better the water use, keeping in mind that ETc have not reduced in the same proportion. Regarding main and secondary schedules for maize the results for soil water balance show that main schedule maize had an increased water consumption (higher ETc) when compared to secondary schedule. The Es component was lower than 26% of ETc, for bean and soybean, and lower than 9% of ETc for maize, indicating the positive effect of mulching. / Para contornar períodos de secas e de baixa disponibilidade hídrica, a irrigação deficitária constitui-se em uma ferramenta importante, desde que aplicada nos períodos menos sensíveis das culturas, a fim de reduzir os impactos sobre a produtividade das culturas. Além disso, a irrigação deficitária pode ser mais eficiente quando se compreende o modo como ocorre a perda de água pelas plantas, a evapotranspiração das culturas (ETc), que se divide em evaporação do solo (Es) e transpiração da cultura (Tc). Os objetivos deste trabalho consistiram em (a) realizar o balanço hídrico do solo cultivado com diferentes culturas (feijão, soja e milho) e determinar os coeficientes de cultura basal (Kcb) mais adequados para as condições do Sul do Brasil; (b) particionar a ETc em Es e Tc para melhor avaliação e entendimento da dinâmica da água no solo ao longo do ciclo das culturas; (c) avaliação da produtividade da água (WP) considerando diferentes níveis de irrigação deficitária; (d) comparação de cenários entre cultivo de safra e safrinha no que se refere ao consumo de água pelas plantas. Para isso, utilizou-se o modelo de balanço hídrico SIMDualKc, o qual foi devidamente calibrado e validado, e que utiliza a metodologia dos coeficientes culturais duais (Kc dual). Experimentos foram conduzidos (feijão em 2010/11; milho safrinha em 2010/11; milho safra em 2011/12; e soja em 2014/15), com a imposição de diferentes níveis de déficit hídrico, utilizando a irrigação por gotejamento e com presença de resíduos vegetais na superfície do solo. Os resultados obtidos com as simulações do modelo SIMDualKc apresentaram boa concordância entre os valores de água disponível no solo (ASW) observados e simulados, com valores de coeficiente de regressão (b0) de, em média, 0,98 para feijão, 0,97 para soja, 1,0 para milho safrinha e 1,05 para milho safra. Os valores de Kcb ajustados para as condições locais foram, respectivamente para feijão, soja, milho, para o período inicial (Kcb ini) 0,15; 0,15; 0,2; para o período intermediário (Kcb mid) 1,03; 1,0; 1,12; e para o período final (Kcb end) 0,2 para todas as culturas. Os resultados do balanço hídrico do solo para cada uma das culturas demonstraram que quanto menor a quantidade de água aplicada nas plantas, melhor uso foi feito desta água pelas plantas, tendo em vista que a ETc não reduziu-se na mesma proporção. No que se refere a comparação de cenários entre milho safra e safrinha, os resultados do balanço hídrico do solo também demonstraram que o milho cultivado durante a época de safra teve um maior consumo de água (maior ETc) quando comparado ao milho cultivado no período de safrinha. O componente Es foi inferior a 26% da ETc, para feijão e soja, e inferior a 9% da ETc para milho safra e safrinha, indicando assim o efeito positivo da utilização de resíduos vegetais sobre a superfície do solo.

Traditional irrigation was practiced in Ethiopia since time immemorial. Despite this, water productivity in the sector remained low. A survey on the Godino irrigation scheme revealed that farmers used the same amount of water and intervals, regardless of crop species and growth stage. In an effort to improve the water productivity, two traditional irrigation scheduling methods were compared with two scientific methods, using furrow irrigation. The growth performance and tuber yield of potato (cv. Awash) revealed that irrigation scheduling using a neutron probe significantly outperformed the traditional methods, followed by the SWB model Irrigation Calendar. Since the NP method involves high initial cost and skills, the use of the SWB Calendar is suggested as replacement for the traditional methods. SWB is a generic crop growth model that requires parameters specific to each crop, to be determined experimentally before it could be used for irrigation scheduling. It also accurately describes deficit irrigation strategies where water supply is limited. Field trials to evaluate four potato cultivars for growth performance and assimilate partitioning, and onions' critical growth stages to water stress were conducted. Crop-specific parameters were also generated. Potato and onion crops are widely grown at the Godino scheme where water scarcity is a major constraint. These crop-specific parameters were used to calibrate and evaluate SWB model simulations. Results revealed that SWB model simulations for Top dry matter (TDM), Harvestable dry matter (HDM), Leaf area index (LAI), soil water deficit (SWD) and Fractional interception (FI) fitted well with measured data, with a high degree of statistical accuracy. The response of onions to water stress showed that bulb development (70-110 DATP) and bulb maturity (110-145) stages were most critical to water stress, which resulted in a significant reduction in onion growth and bulb yields. SWB also showed that onion yield was most sensitive to water stress during these two stages. An irrigation calendar, using the SWB model, was developed for five different schemes in Ethiopia, using long-term weather data and crop-specific parameters for potatoes and onions. The calendars revealed that water depth varied, depending on climate, crop type and growth stage. / Thesis (PhD)--University of Pretoria, 2009. / Plant Production and Soil Science / unrestricted

A series of field, rainshelter, growth cabinet and modelling studies were conducted to investigate hot pepper response to different irrigation regimes and row spacings; to generate crop-specific model parameters; and to calibrate and validate the Soil Water Balance (SWB) model. Soil, climate and management data of five hot pepper growing regions of Ethiopia were identified to develop irrigation calendars and estimate water requirements of hot pepper under different growing conditions. High irrigation regimes increased fresh and dry fruit yield, fruit number, harvest index and top dry matter production. Yield loss could be prevented by irrigating at 20-25% depletion of plant available water, confirming the sensitivity of the crop to mild soil water stress. High plant density markedly increased fresh and dry fruit yield, water-use efficiency and dry matter production. Average fruit mass, succulence and specific leaf area were neither affected by row spacing nor by irrigation regimes. There were marked differences among the cultivars in fruit yields despite comparable top dry mass production. Average dry fruit mass, fruit number per plant and succulence were significantly affected by cultivar differences. The absence of interaction effects among cultivar and irrigation regimes, cultivars and row spacing, and irrigation regimes and row spacing for most parameters suggest that appropriate irrigation regimes and row spacing that maximize productivity of hot pepper can be devised across cultivars. To facilitate irrigation scheduling, a simple canopy cover based procedure was used to determine FAO-type crop factors and growth periods for different growth stages of five hot pepper cultivars. Growth analysis was done to calculate crop-specific model parameters for the SWB model and the model was successfully calibrated and validated for five hot pepper cultivars under different irrigation regimes or row spacings. FAO basal crop coefficients (Kcb) and crop-specific model parameters for new hot pepper cultivars can now be estimated from the database, using canopy characteristics, day degrees to maturity and dry matter production. Growth cabinet studies were used to determine cardinal temperatures, namely the base, optimum and cut-off temperatures for various developmental stages. Hot pepper cultivars were observed to require different cardinal temperatures for various developmental stages. Data on thermal time requirement for flowering and maturity between plants in growth cabinet and open field experiments matched closely. Simulated water requirements for hot pepper cultivar Mareko Fana production ranged between 517 mm at Melkassa and 775 mm at Alemaya. The simulated irrigation interval ranged between 9 days at Alemaya and 6 days at Bako, and the average irrigation amount per irrigation ranged between 27.9 mm at Bako and 35.0 mm at Zeway. / Thesis (PhD)--University of Pretoria, 2010. / Plant Production and Soil Science / unrestricted

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.

This thesis investigates the abiotic control of carbon (C) and water vapour fluxes (FCO₂ and E, respectively) in a New Zealand Pinus radiata D. Don plantation and a nearby clearcut. It concentrates on the limitation of these fluxes imposed by growing season soil water deficit. This results from low precipitation (658 mm a⁻¹) in combination with a limited root zone water storage capacity of the very stony soil (> 30% by volume). The thesis analyses results from seven eddy covariance flux measurement campaigns between November 1994 and March 1996. The study site was located in Balmoral Forest, 100 km north-west of Christchurch (42° 52' S, 172° 45' E), in a (in November 1994) 8-year-old stand. One set of measurements was conducted in an adjacent clearcut. Ecosystem flux measurements were accompanied by separate measurements of ground fluxes and of the associated environmental variables. Flux analysis focussed on the underlying processes of assimilation (Ac), canopy stomatal conductance (Gc) and respiration (Reco), using biophysical models coupled to soil water balance and temperature subroutines. Aiming to link time inegrated net ecosystem C (NEP) to tree growth, sequestration in tree biomass (NPP) was quantified by regular measurements of stem diameter using allometric relationships. Average rates of FCO₂ and E were highest in spring (324 mmol m⁻² d⁻¹ and 207 mol m⁻² d⁻¹, respectively) when the abiotic environment was most favourable for Gc and Ac. During summer, fluxes were impeded by the depletion of available soil water (θ) and the co-occurrence of high air saturation deficit (D) and temperature (T) and were equal or smaller than during winter (FCO₂ = 46 mmol m⁻² d⁻¹ in summer and 115 mmol m⁻² d⁻¹ in winter; E = 57 and 47 mol m⁻² d⁻¹, respectively). With increasingly dry soil, fluxes and their associated ratios became predominantly regulated by D rather than quantum irradiance, and on particularly hot days the ecosystem was a net C source. Interannually, forest C and water fluxes increased strongly with rainfall, and the simultaneously reduced D and T. For two succeeding years, the second having 3 % more rain, modelled NEP was 515 and 716 g C m⁻² a⁻¹, Ac 1690 and 1841 g C m⁻² a⁻¹ and Reco 1175 and 1125 g C m⁻² a⁻¹. NEP / E increased in wetter (and cooler) years (1.3 and 1.5 g kg⁻¹), reflecting a relatively larger gain in NEP. Responding mainly to increased rainfall during commonly dry parts of the year (ie summer), and reflecting the otherwise benign maritime climate of New Zealand, NEP during the winter months could exceed NEP during the middle of the notional tree growing season. Annual Ac, NEP, and NPP were strongly linearly related. This relation did not hold during bi-weekly periods when the processes of intermediate C storage were influential. Separate knowledge of tree growth and C fluxes allowed quantification of autotrophic, and heterotrophic respiration (Rhet≈ 0.4 NEP), as well as fine-root turnover (≈0.2 NEP). The ratio of NEP and stem volume growth was conservative (0.24 t C m⁻³) and allows a direct connection to be made between ecosystem carbon fluxes and forest yield tables. In the absence of living roots, the clearcut flux measurements demonstrated the expected limitation of Rhet by soil temperature (Ts) and θ. However, an additional 'pumping effect' was discovered at the open site whereby turbulence increased CO₂ efflux considerably when the soil surface was wet. Accounting for the combined effects of Ts, θ and turbulence, annual Rhet at the clear-cut site (loss to the atmosphere) was »50 % of NEP (C sequestered from the atmosphere) in the nearby forest. Clearly, there is an important contribution of C fluxes during early stages of ecosystem development to the total C sequestered over the lifetime of a plantation.