Early Stages Of Crop Growth Research Articles

Comparative values of various wastewater streams as a soil nutrient source

In order to assess whether wastewaters from different industries (winery, abattoir, dairy and municipal) could be used safely to irrigate agricultural crops, a pot experiment in glass house was conducted in a sandy clay loam soil (pH = 6.12) from South Australia. Different concentrations (0, 0.05, 5, 25, 50, 75 and 100%) of the wastewaters diluted in an ordinary tap water were applied to soils sown with sunflower and maize seeds, and the effect of these irrigation treatments were evaluated at the early crop growth stages by recording the biomass yields, plant mineral nutrient contents, and also the soil chemical properties. Results showed that the winery effluent reduced the early growth of maize and sunflower when applied without any dilution, but increased yields of both plants when applied at 25% dilution with tap water. At this dilution of the winery wastewater, 80% more dry shoot yield (DSY) of sunflower and 58% more DSY of maize were obtained in comparison to the application of 100% concentration of the wastewater. Abattoir wastewater showed the highest yields at 100% concentration. Furthermore, municipal effluent did not show any inhibitory effect on both the crops. It was observed that metal contents in both the crops were different due to the application of different wastewaters, but did not exceed any toxic level. This study demonstrated that abattoir wastewater as such, and winery and dairy wastewaters at appropriate dilutions could be used for irrigation in agricultural fields to enhance crop productivity.

Modelling sugarcane nitrogen uptake patterns to inform design of controlled release fertiliser for synchrony of N supply and demand

The use of controlled release fertilisers (CRF) is being promoted in the Australian sugarcane industry to improve nitrogen (N) use efficiency and reduce N losses through better matching of N release with crop N demand. Little is known, however, about the required synchrony due to limited information on both N uptake patterns of sugarcane and N release patterns from CRF under different crop growing conditions. This paper uses APSIM scenario modelling to characterise N uptake patterns of sugarcane plant and ratoon crops in response to seasonal variability and different climatic and management conditions (e.g. level of water and N input, time of planting/ratooning) at five sites within the Australian sugarcane growing region. The results showed considerable variations in crop N uptake patterns across seasons, sites and under different management scenarios. However, for a given site, crop N uptake patterns during the early crop growth stage varied little between seasons (<0.5gN/m2). All the simulated N uptake patterns showed an initial lag period with little N uptake (average <1.7g/m2), followed by a relatively sudden transition to a rapid and linear uptake period with the rate and duration of the linear phase depending on management, climatic and soil conditions. Over the course of the season the variation in total N uptake increased especially when the sugarcane system had a limited irrigation allocation or was rainfed. These N uptake patterns could be used to inform the design and management of CRF to optimise synchronisation with sugarcane crop N demand. The predicted average lag periods ranged from 55days to 137days. The average lag period was shorter for the ratoon crops (55–83days) as compared to that for the plant crops (79–137days) and shorter for later planted or ratooned crops that experienced warmer temperatures in the first months. Temperature also contributed to a location effect, which was particularly strong for plant crops where, for example, the average lag period for early plant crops ranged from 102days for the most northern tropical site to 137days for the most southern subtropical site. These differences need to be considered in the design of CRF release patterns and management of timing of application. The predicted average maximum linear N uptake rate ranged from 0.25 to 0.38gN/m2/day and driven by direct and indirect effects of solar radiation input. The greater variations in the final total N uptake amount present uncertainty on how much CRF needs to be applied ahead of different seasons. Better seasonal climate forecasting may enable a more precise estimation of total season N requirement by the crop and the amount of CRF required.

Evaluation of fungicides and herbicides against groundnut collar rot pathogen Aspergillus niger under in vitro conditions

Collar rot of groundnut is caused by Aspergillus niger Van Tieghem. It is a soilborne pathogen, usually the occurrence of collar rot disease during the early stages of crop growth and results in high seedling mortality. The collar rot pathogen produces both seed rot (pre-emergence) and seedling blight symptoms (post-emergence). In case of seed rot, black masses of mycelium were seen on the surface of seed. Later, the pathogen causes rotting of seed. Rotten seed do not emerge from the soil. Collar rot affected seedlings show a circular brownish spot on cotyledon region. Later, the discoloured area rapidly disintegrates spreading to the stem and hypocotyl. The affected plants show general wilting, rotting just below the ground level. An experiment was conducted under in vitro conditions to evaluate the fungicides against the collar rot pathogen apart from these fungicides, some herbicides also evaluated to test their non-target effect against collar rot pathogen. A total of six fungicides and eight herbicides were evaluated by using poisoned food technique. Maximum inhibition (100%) of radial growth of A. niger was obtained with tebuconazole at recommended and half recommended dosage and least inhibition was obtained with mancozeb and azoxystrobin. Among herbicides pendimethalin was shown maximum inhibition (100%) against A. niger and least inhibition was observed with herbicide imazythapyr and imazythapyr + imazamox.

Effects of Biochar on Surface Albedo and Soil Respiration in Suburban Agricultural Soil

Biochar application to soils is currently considered as a means of mitigating climate change by sequestering C, which withdraws CO2 from the atmosphere and consequently influences the trend of global climate change. However, only a few studies have been done on surface albedo variations on farmland, it might be true that the application of biochar to soil could induce a radiative forcing by changing the surface albedo. Based on this background, this study aiming at the characterization of seasonal changes in albedo on the farmland both with plants and without plants, and its effect on soil temperature, soil moisture, soil respiration and soil organic carbon fractions. There were 3 major treatments in the experiment with 3 repetition of each major treatment, namely, CK (the control treatment), BC0.5 (biochar applied at 0.5 kg·(m2·a)-1) and BC4.5 (biochar applied at 4.5 kg·(m2·a)-1). Each major treatment contained 2 sub-treatments, which were crop cultivation (+) and non-cultivation (-). The experiment results showed that in the early stage of crop growth (maize seedling stage to jointing stage, wheat seedling stage to winter period), the surface albedo of BC4.5+and BC0.5+significantly decreased compared with CK +(P<0.05). The biggest surface albedo decline rates of BC4.5 + and BC0.5 + in winter wheat season were 23.7%, 17.9% and 44.5%, 44.9% in summer maize season. The leaf area index of each treatment was remarkably correlated with the surface albedo. The shadow produced by the development of crop canopy structure would cover the change of surface color induced by the input of biochar. Under the condition of bare land, the surface albedo of biochar treatment was significantly decreased compared with the control treatment(P<0.05). Compared with the control treatments, the soil CO2 flux of the biochar treatments was significantly increased(P<0.05). With the extension of time, the growth rate of soil CO2 flux of biochar treatment was decreased gradually. The increase from BC4.5 + to CK + was gradually reduced from 276.7% to 36.1%, and the increase of BC4.5-from to CK-was significantly reduced from 163.5% to 39.8%. The increase of soil CO2 flux could be derived from the mineralization of the readily decomposed carbon fractions in the biochar-soil system. The decrease of surface albedo caused by the input of biochar had no direct effect on soil respiration, and the input of biochar could reduce the temperature sensitivity of soil respiration. This result could provide a foundation for the verification of the chemical and biological stability of biochar.

Diet of generalist predators reflects effects of cropping period and farming system on extra- and intraguild prey.

The suppression of agricultural pests by natural enemies, including generalist arthropod predators, is an economically important regulating ecosystem service. Besides pests, generalist predators may also consume non-pest extraguild and intraguild prey, which can affect their impact on pest populations. This may either reduce the impact of generalist predators on pest populations, because they are diverted from pest predation, or increase it, as it helps them survive periods of low pest availability. However, the availability of pest prey and alternative, non-pest prey can vary over the crop growing season and between farming systems, potentially affecting predator-prey interactions and the levels of biological control. We have limited information about how farming systems and environmental variation over the crop growing season influence predator diets. This limits our ability to predict the importance of generalist predators as natural enemies of agricultural pests. Here we utilize molecular gut content analyses to assess detection frequencies of extra- and intraguild prey DNA in generalist predator communities in replicated organically and conventionally managed cereal fields at two key periods of the cropping season for aphid biological control. This is done in order to understand how farming system, crop season, prey availability and predator community composition determine the composition of predator diets. Aphid pests and decomposers (springtails) were equally important prey for generalist predators early in the growing season. Later in the season, the importance of aphid prey increased with increasing aphid densities while springtail predation rates were positively correlated to abundance of this prey at both early and late crop growth stages. Intraguild predation was unidirectional: carabids fed on spiders, whereas spiders rarely fed on carabids. Carabids had higher detection frequencies for the two most common spider families in organically compared to conventionally managed fields. Our study documents that predation by generalist predator communities on aphid pests increases with pest numbers independently of their generally widespread consumption of alternative, non-pest prey. Therefore, conservation strategies in agricultural fields could promote biological control services by promoting high levels of alternative non-pest prey for generalist predator communities.

Response of Maize (Zea mays L.) Secondary Growth Parameters to Conservation Agriculture and Conventional Tillage Systems in Zimbabwe

&lt;p&gt;Previous, research focused mainly on the effects of conservation agriculture (CA) and conventional practices (CP) on crop yield mostly. A study was conducted at five sites in Zimbabwe from 2012 to 2014 to investigate effects of CA and CP practices on emergence, chlorophyll content, early vigour and grain yield of different maize varieties using 12 hybrids and 4 open pollinated varieties (OPVs). The experiment was laid as a 4 × 4 alpha lattice design with three replications. Emergence was higher under CA (75%) at University of Zimbabwe (UZ) in 2012/13 and Domboshawa Training Centre (DTC) (67%) compared to CP (71% and 39% respectively). Lower early plant vigour was observed under CA compared to CP at most sites. CA had lower leaf chlorophyll content during the early crop growth stages compared to CP. However, at some instances, CA had higher leaf chlorophyll content (45 units) than CP (35 units) at 78 days after sowing in Zimuto 2012/13. For maize yield, CA outperformed CP on a sandy loamy soil (3050 kg ha&lt;sup&gt;-1&lt;/sup&gt; vs 2656 kg ha&lt;sup&gt;-1&lt;/sup&gt;) and clay soil (4937 kg ha&lt;sup&gt;-1&lt;/sup&gt; vs 4274 kg ha&lt;sup&gt;-1&lt;/sup&gt;). However, on a sandy soil, CP outperformed CA (1764 vs 1313 kg ha&lt;sup&gt;-1&lt;/sup&gt;). Our results suggest that tillage effects on early maize plant vigor, leaf chlorophyll content and the final yield can be site and season specific. Furthermore, a delay of nutrient release for plant uptake under CA systems was found and potentially implies investigations of new fertilization strategies for such cropping systems.&lt;/p&gt;

Seasonal and inter-annual variability of soil moisture stress function in dryland wheat field, Australia

It is assumed that the ratio of actual evapotranspiration (AET) to potential evapotranspiration (PET) is mostly controlled by the soil water content available for ET. This control is formulated using the soil moisture stress function (SSF), where the evaporative fraction (EF) or the fraction of the AET to PET (fPET) is assumed to be either a linear or a non-linear function of soil moisture. We examine the effectiveness of the soil moisture stress function to quantify soil moisture control on EF or fPET over a dryland wheat field in Victoria, Australia. Micrometeorological observations from two cropping seasons were used for the analysis. The efficacy of a root-density-weighted soil moisture estimate in predicting EF and fPET was investigated as against the commonly assumed fixed-depth root zone soil moisture. However, results indicate a strong relationship between EF and available soil water fraction (AWF) in the root zone only when solar radiation is higher than 5MJ/m2/day. As the rooting depth increases with vegetation growth, SSF exhibits the strongest correlation with AWF for increasing soil profile depth. In the early and harvesting crop growth stages, ET is constrained mostly by surface soil moisture (0–5cm). In the mid-growth stages, ET is strongly influenced by soil moisture in the root zone (0–60cm). The shape of SSF, however, changes significantly between the two years (2012 and 2013). It is inferred that different temporal rainfall patterns between the years caused wheat’s different response to water stress.

Seasonal Dynamics, Influence of Weather Factors and Forecasting of Cotton Sap Feeders in North India

Analyses of the scenario of cotton sap feeders [leaf hoppers, Amrasca biguttula biguttula (Ishida), thrips, Thrips tabaci Lindeman and whiteflies, Bemisia tabaci Gennadius] based on their population dynamics (numbers/three leaves/plant) for north zone cotton growing locations viz., Faridkot (30.40°N, 74.45°E), and Ludhiana (30.91°N, 75.85°E) of Punjab, Hisar (29.15°N, 75.70°E) of Haryana and Sriganganagar (29.92°N, 73.88°E) of Rajasthan indicated significantly higher A. biguttula biguttula infestation during 2013 (7.0) and 2014 (14.0) over previous eight seasons, increasing whitefly incidence after every two years, and declining T. tabaci infestation at Faridkot (Punjab). Bemisia tabaci incidence was highest during 2013 (26.4) and 2014 (26.9) at Hisar. Peak population and period of sap feeders varied across locations and population between seasons of the same location differed during early and late crop growth stages. The importance of sap feeders was of the order: A. biguttula biguttula > B. tabaci > T. tabaci at Ludhiana (Punjab). Thrips tabaci and B. tabaci were dominant at Sriganganagar (Rajasthan). Increasing trend of A. biguttula biguttula, T. tabaci and B. tabaci were observed over years at all locations but for declining population levels of T. tabaci at Ludhiana (Punjab) and Sriganganagar (Rajasthan). Multiple linear regression forecast models in respect of sap feeders for the four locations were developed using SAS 9.3. Minimum and maximum temperatures besides rainfall significantly predicted the population of each sap feeder for the current, 1 and 2 weeks after.

Changes to soil water content and biomass yield under combined maize and maize-weed vegetation with different fertilization treatments in loam soil

Abstract Especially during early developmental stages, competition with weeds can reduce crop growth and have a serious effect on productivity. Here, the effects of interactions between soil water content (SWC), nutrient availability, and competition from weeds on early stage crop growth were investigated, to better understand this problem. Field experiments were conducted in 2013 and 2014 using long-term study plots on loam soil in Hungary. Plots of maize (Zea mays L.) and a weed-maize combination were exposed to five fertilization treatments. SWC was observed along the 0–80 cm depth soil profile and harvested aboveground biomass (HAB) was measured. Significant differences were found between SWC in maize and maize-weed plots. In all treatments, measured SWC was most variable in soil depths of up to 50 cm, and at the 8–10 leaves (BBCH19) growth stage of the crop. The greatest depletion of SWC was detected within PK treatments across the entire soil profile and under both vegetation types, with depletion also considerable under NPK and NP treatments. Biomass growth was significantly influenced by weeds in treated plots between the BBCH 13 and 19 phenological stages, but water availability did not hamper growth rates in non-fertilized conditions. These findings suggest that, at early stages of crop growth, SWC model simulations need to include better characterisation of depth- and structure-dependent soil water uptake by vegetation.

A preliminary study of the effects of plastic film-mulched raised beds on soil temperature and crop performance of early-sown short-season spring maize (Zea mays L.) in the North China Plain

To identify a strategy for earlier sowing and harvesting of spring maize (Zea mays L.) in an alternative maize–maize double cropping system, a 2-year field experiment was performed at Quzhou experimental station of China Agricultural University in 2014 and 2015. A short-season cultivar, Demeiya number 1 (KX7349), was used in the experiment. Soil temperature to 5cm depth in the early crop growth stage, crop growth, crop yield, and water use of different treatments (plastic film-mulched raised bed (RF) and flat field without plastic film mulching (CK) in 2014; RF, plastic film-mulched flat field (FF), and CK in 2015) were measured or calculated and compared. Soil temperature in the film-mulched treatments was consistently higher than that in CK (1.6–3.5°C in average) during the early growth stage. Crops in plastic film-mulched treatments used 214 fewer growing-degree days (GDDs) in 2014 and 262 fewer GDDs in 2015. In 2014, the RF treatment yielded 32.7% higher biomass than CK, although its 9.4% higher grain yield was not statistically significant. Also, RF used 17.9% less water and showed 33.1% higher water use efficiency (WUE) than CK. In 2015, RF and FF showed 56.2% and 49.5% higher yield, 15.0% and 4.5% lower water use (ET), and 63.4% and 75.7% higher WUE, respectively, than CK. RF markedly increased soil temperature in the early crop season, accelerated crop growth, reduced ET, and greatly increased crop yield and WUE. Compared with FF, RF had no obvious effect on crop growth rate, although soil temperature during the period between sowing and stem elongation was slightly increased. However, RF resulted in lower ET and higher WUE than FF. Effects of RF on soil water dynamics as well as its cost-effectiveness remain topics for further study.

Evaluation of finger millet genotypes for partial resistance to leaf blast caused by Pyricularia grisea

Blast of finger millet (ragi) caused by Pyricularia grisea is disastrous disease to limit the potential yield levels in the farmers field. The pathogen affects the crop at all growth stages and the most susceptible stage for leaf blast is seedling stage. Use of resistant cultivars for minimizing losses due to leaf blast at early stage of crop growth is a viable and economical alternative. In the present study, partial resistance to leaf blast in fourteen genotypes of finger millet was assessed under field conditions. None of the genotypes were highly resistant to leaf blast. However, two genotypes namely PR 10-30 and VL 368 were shown resistance. Seven genotypes namely VR 988, VL 353, VL 348, TNAU 1214, GPU 45, VL 369, KOPM 942 were found moderately resistant, three namely PPR 2773, KRI 007-01, VR 708 were susceptible and two namely TNAU 1226 and REC 69 were highly susceptible. The correlation coefficients between leaf blast severities (LBS) with different components of partial resistance of slow blasting were significant. Low value of coefficient of infection (CI), apparent infection rate (r), area under disease progress curve (AUDPC), lesion number (LN), lesion area (LA), lesion circumference (LC) and high value of incubation period (IP) were recorded in resistant genotypes of finger millet, whereas, higher values of CI, r, AUDPC, LN, LA, LC and low values of IP were recorded in highly susceptible genotypes. A significant positive correlation was found in leaf blast severity with CI (r=0.948*), r (r=0.829*), AUDPC (r=0.998*), LN (r=0.967*), LA (r=0.957*), LC (r=0.976*) whereas IP (r=-0.825*) was negatively correlated with blast resistance. PR 10-30 and VL 368 showed higher degree of partial resistance or slow blasting resistance against P. grisea infection on finger millet.

Impact of post-anthesis glyphosate on woolly cupgrass seed production, seed weight and seed viability

Nurse, R. E., Darbyshire, S. J. and Simard, M.-J. 2015. Impact of post-anthesis glyphosate on woolly cupgrass seed production, seed weight and seed viability. Can. J. Plant Sci. 95: 1193–1197. Herbicides are generally applied at early stages of crop and weed growth to protect crop yield. Few studies have evaluated the effect of late (post-anthesis) applications of glyphosate as a management option to limit the seed production of weed escapes, such as woolly cupgrass (Eriochloa villosa). We propagated woolly cupgrass under greenhouse conditions and then applied three glyphosate treatments post-anthesis including: (1) an untreated control; (2) 900 g a.e. ha−1; and (3) 1800 g a.e. ha−1. Terminal inflorescences were collected 21 d after glyphosate application, and seed production, seed weight and embryo viability were assessed. Post-anthesis glyphosate applications did not influence seed production, but reduced seed weight and viability by 50 and 96%, respectively. Therefore, glyphosate applied just before the woolly cupgrass inflorescence begins to emerge from the leaf sheath (as late as the R1 stage in soybeans) is an effective strategy to manage woolly cupgrass reproduction and stop viable seeds from entering the soil seed bank or other dispersal pathways.

Growth Behavior, Nutrient Harvest Index, and Soil Fertility in Okra-Pea Cropping System as Influenced by AM Fungi, Applied Phosphorus, and Irrigation Regimes in Himalayan Acidic Alfisol

The impact of arbuscular mycorrhizal fungi (AMF), inorganic phosphorus (P), and irrigation regimes was studied in an okra (Abelmoschus esculentus)–pea (Pisum sativum) cropping system in an acidic Alfisol. Experimentation was carried out at Palampur, India, in a randomized bock design (RBD), replicated three times with fourteen treatments comprising AM fungi (Glomus mosseae), inorganic phosphorus (50, 75, and 100% soil-test-based recommended P dose), irrigation regimes (at 40 and 80% available water capacity), generalized recommended NPK and irrigations (GRD), and farmers’ practice. Effects of AM fungi on plant height, leaf area index (LAI), and dry-matter accumulation (DMA) were nominal at early crop growth stage, i.e., 50 DAS (days after sowing). However, at 100 DAS, AMF imbedded treatments led to higher plant height (4%), LAI (3%), and DMA (6%) in okra, whereas in pea the magnitude of increase in these parameters following AMF inoculation was 6, 5, and 8%, respectively, over non-AMF counterparts. AMF + 75% soil-test-based P dose at either of these irrigation regimes gave statistically similar yields in both okra and pea as that obtained under 100% soil-test-based P dose at either of two irrigation regimes, thus indicating an economy of about 25% in soil-test-based P dose. Regarding nutrient harvest index in okra and pea, statistically similar values were registered with most nutrients under both AMF inoculated and non-AMF counterparts. In the case of okra, P harvest index was registered less by 3% with AMF inoculation; however, its magnitude increased by 3% in pea following AMF inoculation compared to non-AMF counterparts at similar levels of P and irrigation. At completion of two cycles of okra-pea system, AMF imbedded treatments did not alter available soil nutrient status significantly in comparison to non-AMF counterparts. Overall, current study suggests that practice of AMF inoculation has great potential in enhancing growth parameters for better productivity, fertilizer-P economy, and nutrient harvest efficiency in okra-pea production system in Himalayan acidic Alfisol.

Monsoon variability, crop water requirement, and crop planning for kharif rice in Sagar Island, India.

In the Sagar Island of Bay of Bengal, rainfed lowland rice is the major crop, grown solely depending on erratic distribution of southwest monsoon (SM) rainfall. Lack of information on SM rainfall variability and absence of crop scheduling accordingly results in frequent occurrence of intermittent water stress and occasional crop failure. In the present study, we analyzed long period (1982-2010) SM rainfall behavior (onset, withdrawal, rainfall and wetness indices, dry and wet spells), crop water requirement (CWR, by Food and Agriculture Organization (FAO) 56), and probability of weekly rainfall occurrence (by two-parameter gamma distribution) to assess the variability and impact on water availability, CWR, and rice productivity. Finally, crop planning was suggested to overcome monsoon uncertainties on water availability and rice productivity. Study revealed that the normal onset and withdrawal weeks for SM rainfall were 22nd ± 1 and 43rd ± 2 meteorological weeks (MW), respectively. However, effective monsoon rainfall started at 24th MW (rainfall 92.7 mm, p > 56.7 % for 50 mm rainfall) and was terminated by the end of 40th MW (rainfall 90.7 mm, p < 59.6 % for 50 mm rainfall). During crop growth periods (seed to seed, 21st to 45th MW), the island received an average weekly rainfall of 65.1 ± 25.9 mm, while the corresponding weekly CWR was 47.8 ± 5.4 mm. Despite net water surplus of 353.9 mm during crop growth periods, there was a deficit of 159.5 mm water during MW of 18-23 (seedling raising) and MW of 41-45 (flowering to maturity stages). Water stress was observed in early lag vegetative stage of crop growth (32nd MW). The total dry spell frequency during panicle initiation and heading stage was computed as 40 of which 6 dry spells were >7 days in duration and reflected a significant (p < 0.05) increasing trend (at 0.22 days year(-1)) over the years (1982-2010). The present study highlights the adaptive capacity of crop planning including abiotic stress-tolerant cultivars to monsoon rainfall variability for sustaining rainfed rice production vis-à-vis food and livelihood security in vulnerable islands of coastal ecosystem.

Development of Chinese Crop Monitoring Model Using Photosynthetic Production Index

For monitoring the early stage of crop growth in China, this paper presents a photosynthesis-based monitoring model for grain production. Not only the normalized difference vegetation index and elements such as the growing degree day are considered, the factors of sunshine and the cost of water resource are also considered in the model.

Assessment of crop foliar nitrogen using a novel dual-wavelength laser system and implications for conducting laser-based plant physiology

Advanced technologies for improved nitrogen (N) fertilizer management are paramount for sustainably meeting future food demands. Green laser systems that measure pulse return intensity can provide more reliable information about foliar N than can traditional passive remote sensing devices during the critical early crop growth stages (e.g., before canopy closure when vegetation and soil signals are spectrally mixed) when further decisions regarding N management can be made. However, current green laser systems are not designed for agricultural applications and only employ a single green laser wavelength, which may limit applications because many factors that require normalization techniques can affect pulse return intensity. Here, we describe the design of a tractor-mountable, green (532nm)- and red (658nm) dual wavelength laser system and evaluate the potential of an additional red reference wavelength to improve laser based estimates of foliar N by calculating laser spectral indices based on ratio combinations of green laser return intensity (GLRI) and red laser return intensity (RLRI). We hypothesized that such laser spectral indices aid in accounting for factors that confound laser based foliar N estimates including variations in leaf angle, measurement distance, soil returns, and mixed edge returns. Leaf level measurements in winter wheat (Triticum aestivum) revealed that the two laser spectral indices improved the relationship with foliar N (r2>0.71, RMSE<0.28%) compared to the sole use of GLRI (r2=0.47, RMSE=0.38%). Laboratory measurements also showed that laser spectral indices reduced the effect of measurement distance on laser readings and allowed leaf returns to be better separated from edge returns and soil returns. However, laboratory measurements showed that laser spectral indices did not account for variations in leaf angle, possibly explaining the weak relationships (r2<0.36, RMSE=0.49%) between foliar N and laser spectral indices observed when employing the laser system under field conditions. In fact, the strongest relationship at the field canopy level was shown for GLRI (r2=0.65, RMSE=0.37%) alone. Laboratory measurements suggest that the better performance of GLRI compared to ratio-based laser spectral indices may result from pronounced differences in the leaf-level bidirectional reflectance distribution factor (BRDFleaf) between the green and red laser wavelengths, thus confounding leaf angle effects so that they are not cancelled when calculating laser spectral indices. This finding suggests that the small spot size of the laser pulses (⩽5mm diameter) interacts with BRDFleaf at very fine scales, therefore causing differential, wavelength-specific scattering effects. Additional study of BRDFleaf at the mm scale is therefore warranted, and should be carefully considered in future development and use of multi-wavelength laser systems for remotely sensing foliar biochemistry.

Estimation of crop gross primary production (GPP): fAPARchl versus MOD15A2 FPAR

Photosynthesis (PSN) is a pigment level process in which antenna pigments (predominately chlorophylls) in chloroplasts absorb photosynthetically active radiation (PAR) for the photochemical process. PAR absorbed by foliar non-photosynthetic components is not used for PSN. The fraction of PAR absorbed (fAPAR) by a canopy/vegetation (i.e., fAPARcanopy) derived from the Moderate Resolution Imaging Spectroradiometer (MODIS) images, referred to as MOD15A2 FPAR, has been used to compute absorbed PAR (APAR) for PSN (APARPSN) which is utilized to produce the standard MODIS gross primary production (GPP) product, referred to as MOD17A2 GPP. In this study, the fraction of PAR absorbed by chlorophyll throughout the canopy (fAPARchl) was retrieved from MODIS images for three AmeriFlux crop fields in Nebraska. There are few studies in the literature that compare the performance of MOD15A2 FPAR versus fAPARchl in GPP estimation. In our study MOD15A2 FPAR and the retrieved fAPARchl were compared with field fAPARcanopy and the fraction of PAR absorbed by green leaves of the vegetation (fAPARgreen). MOD15A2 FPAR overestimated field fAPARcanopy in spring and in fall, and underestimated field fAPARcanopy in midsummer whereas fAPARchl correctly captured the seasonal phenology. The retrieved fAPARchl agreed well with field fAPARgreen at early crop growth stage in June, and was less than field fAPARgreen in late July, August and September. GPP estimates with fAPARchl and with MOD15A2 FPAR were compared to tower flux GPP. GPP simulated with fAPARchl was corroborated with tower flux GPP. Improvements in crop GPP estimation were achieved by replacing MOD15A2 FPAR with fAPARchl which also reduced uncertainties of crop GPP estimates by 1.12–2.37gCm−2d−1.

Determination of Critical Tissue Phosphorus Concentration in Mungbean and Urdbean for Plant Diagnostics

A pot experiment was conducted to study the effect of phosphorus (P) nutrition on mungbean and urdbean genotypes and to determine the critical concentration of tissue phosphorus at different growth stages for plant diagonostic and P management. There were eight treatments consisting of different levels of P added in the form of monopotassium phosphate (KH2PO4). Destructive plant samples were taken to determine tissue P concentration and plant dry matter at different growth stages. Plant tissue P concentration was found highly correlated with dry matter production in mungbean (r2 = 0.84–0.98) and urdbean (r2 = 0.98–0.998) at corresponding sampling period throughout the growth stages. Considerable variation was observed in critical P concentration with genotypes and leaf position in mungbean and urdbean. Critical P concentration varied between 0.45–0.49 in mungbean and 0.45 to 0.57 in urdbean at early stages of crop growth, and these values declined sharply with advancement in crop growth.

Temporal dynamics of spatial heterogeneity over cropland quantified by time-series NDVI, near infrared and red reflectance of Landsat 8 OLI imagery

Spatial heterogeneity is an important characteristic of the land surface. Because multi-spectral bands are used to describe the land surface, an approach has to be established to characterize the surface spatial heterogeneity from multi-spectral remote-sensing observations. This work aims at quantifying the spatial heterogeneity of cropland using varigorams for multi-temporal NDVI, near infrared (NIR) and red reflectance. A concept of mean length variability is proposed to compare the difference in spatial heterogeneity detected by variables with different magnitudes. The important temporal changes in spatial heterogeneity observed by NDVI, NIR and red bands over cropland are a result of changes in the fraction of vegetation cover. The results indicate the following: (1) the NIR and red variables detect a similar spatial heterogeneity of the cropland with similar values of the mean length variability before the sowing of crops; (2) the NDVI, NIR and red values capture different degrees of spatial heterogeneity when vegetation cover is low; (3) over medium vegetation cover, the NDVI and NIR values capture similar spatial heterogeneity, which is low compared to the red band due to the homogeneity of soil; and (4) the spatial heterogeneity quantified by the NIR value is more heterogeneous than those of the NDVI and red values when vegetation cover is high. The red reflectance is sensitive to soil properties while the NIR reflectance responds to vegetation. The spatial heterogeneity of red reflectance decreases and that of the NIR reflectance increases with the growth of vegetation. The NDVI value shows the greatest heterogeneity in the early stage of crop growth. With an increase in the image pixel size, the spatial heterogeneity quantified by the mean length variability of the NDVI, NIR and red variables tends to be the same.

Relationship between potato yield and the degree of weed infestation

Field experiment was carried out in the years 2002 to 2004 to study the effect of soil tillage methods and weed control techniques with herbicides. Potato yield and degree of weed infestation were investigated using correlation coefficients and linear regression analysis. High negative associations were found between the number of weeds, their fresh and air dry matter, and total potato tuber yield as well as marketable fraction tuber yield. The relationships were negative linear. A higher negative influence of weed infestation on potato yield was found before harvest, compared with early stage of crop growth before closing of potato rows. The presence of weeds was increasing by 1 ton of air weed dry matter per 1 ha furthermore it reduced the marketable fraction tubers yield by, respectively, 0.94 and 1.34 t per 1 ha when recorded before closing of potato rows, and by 2.62 and 3.76 t ha-1 when recorded before potato harvest. To conclude, weeds can affect yield and harvesting of potatoes and may encourage certain pests and diseases. Consequently weed reduction by using two techniques, either mechanical or combination of mechanical and chemical weed control is surely required. Key words: Potato, weed infestation, yield, correlation coefficient, analysis of regression, herbicides.