Crop Growth Status Research Articles

Relationships Between Yield Monitor Data and Airborne Multidate Multispectral Digital Imagery for Grain Sorghum

Remote sensing imagery taken during a growing season not only provides spatial and temporal information about crop growth conditions, but also is indicative of crop yield. The objective of this study was to evaluate the relationships between yield monitor data and airborne multidate multispectral digital imagery and to identify optimal time periods for image acquisition. Color-infrared (CIR) digital images were acquired from three grain sorghum fields on five different dates during the 1998 growing season. Yield data were also collected from these fields using a yield monitor. The images and the yield data were georeferenced to a common coordinate system. Four vegetation indices (two band ratios and two normalized differences) were derived from the green, red, and near-infrared (NIR) band images. The image data for the three bands and the four vegetation indices were aggregated to generate reduced-resolution images with a cell size equivalent to the combine's effective cutting width. Correlation analyses showed that grain yield was significantly related to the digital image data for each of the three bands and the four vegetation indices. Multiple regression analyses were also performed to relate grain yield to the three bands and to the three bands plus the four indices for each of the five dates. Images taken around peak vegetative development produced the best relationships with yield and explained approximately 63, 82, and 85% of yield variability for fields 1, 2, and 3, respectively. Yield maps generated from the image data using the regression equations agreed well with those from the yield monitor data. These results demonstrated that airborne digital imagery can be a very useful tool for determining yield patterns before harvest for precision agriculture.

Modelling of crop growth conditions and crop yield in Poland using AVHRR-based indices

The application of satellite-derived indices for assessment of crop growth conditions in semi-arid countries is well known. In this paper the authors describe the application of these indices outside semi-arid areas, in Poland, a country with a sufficient water supply. Two indices, Vegetation Condition Index (VCI) and Temperature Condition Index (TCI), were computed for the whole country for each week for a period of 14 years. These indices were correlated with cereal yield anomalies for each of 49 regions of Poland. Two critical periods in crop development were found: early spring (14-16 weeks of the year) and early summer (22-25 weeks) when the state of crop development determines the magnitude of yield. The indices computed for these two periods were used in a yield prediction model. The results were compared with data provided by the Central Statistical Office. The average error of cereal yield estimates for 49 regions was lower than 4%.

Soil water drying and recharge rates as affected by tillage under continuous barley and barley-canola cropping systems in northwestern Canada

In areas of the northwestern Canadian Prairies, barley and canola are grown in a short growing season with high rainfall variability. Excessively dry soil in conventional tillage (CT) in dry periods and excessively wet soil in no-tillage (NT) in wet periods could cause a significant decrease in crop production by influencing the availability of soil water. The effects of CT, NT and NT with a 7.5-cm residue-free strip on the planting rows (NTR) on soil water drying (–dW/dt) and recharge (dW/dt) rates were studied in 1992 and 1993 during wet and dry periods to evaluate the impact of NTR, NT and CT systems on soil moisture condition. The soils, Donnelly silt loam and Donnelly sandy loam (both Gray Luvisol) were selected and soil water content by depth was measured by time domain reflectometry. Water retained at 6 matric potentials from –5 to –160 kPa were observed. In the field study, –dW/dt was significantly greater in CT than in NT in the silt loam for the 0- to 30-cm layer during the first 34 d after planting in 1992. The 0- to 30-cm soil layer in CT and NTR dried faster than in NT during a period immediately following heavy rainfall in the silt loam in 1993. The drying coefficient (–Kd ) was significantly greater in CT and NTR than in NT in the silt loam soil in 1993 and in the sandy loam soil in 1992 in the top 30-cm depth. The recharge coefficient (Kr) was significantly greater in NT and NTR than in CT for the silt loam soil. The NTR system increased the –dW/dt by 1.2 × 10-2 to 12.1 × 10-2 cm d-1 in 1992 and 1993 in the silt loam soil and by 10.2 × 10-2 cm d-1 in 1993 in the sandy loam soil as compared with NT. The dW/dt was 8.1 × 10-2 cm d-1 greater in NTR in 1992 and 1993 in the silt loam soil and was 1.9 × 10-2 greater in NTR in 1992 than in CT in the sandy loam soil. The laboratory study indicated that NT soils retained more water than the CT soils. The NTR practice maintained better soil moisture conditions for crop growth than CT in dry periods than NT in wet periods. Compared with NT, the NTR avoided prolonged near-saturated soil conditions with increased soil drying rate under extremely wet soil. Key words: Water drying, water recharge, water depletion, wet and drying periods, hydraulic properties, soil capacity to retain water

Mapping Complex Patterns of Erosion and Stability in Dry Mediterranean Ecosystems

Parametrizing soil reflectance spectra with variables related to specific shape characteristics of the spectral profile permits organic carbon concentrations in soils to be estimated on the basis of regionally validated regression models. An important feature of the approach is that it can not only be applied to continuous spectra but, without notable loss in accuracy, also to the spectral resolution of operational earth observation satellites such as the Landsat-TM or -ETM systems. Using this type of imagery, it can also be shown that soil organic matter is positively correlated to growth conditions for cereal crops in dryland agriculture. Strong correlations with qualitative erosion indicators that can be derived through spectral unmixing approaches demonstrate that soil organic matter is an important indicator for assessing land degradation processes in dry ecosystems from space.

Deficit irrigation and nitrogen effects on maize in a Sahelian environment: II. Shoot growth, nitrogen uptake and water extraction

Maize growth in arid and semiarid regions is often limited by variation in the amount and frequency of irrigation or rainfall. Sub-optimal supply of nitrogen (N) may further curtail growth and development of the crop. Simultaneous optimization of these two inputs provides optimum conditions for crop growth and productivity. A maize ( Zea mays L.) crop was subjected to different periods of deficit irrigation and rates of N in the field on a medium-deep Tropudalf clay loam soil. Water deficit effects on shoot growth, N uptake and water extraction with varying level of N supply were analyzed to determine their inter-relationships. Water deficit was created by withholding irrigation at different stages of crop development. Increasing moisture stress resulted in progressively less leaf area, crop growth rate (CGR), plant height, shoot dry matter and harvest index. Mean increase in above ground biomass was 7.7 and 8.7 kg per mm of water used in the 1996/1997 and 1997/1998 seasons, respectively. Deficit irrigation stress indices (DISI) for above ground biomass when the crop was subjected to a 2 week stress was 11.0 and 20.1 compared to 4 week stress values of 3.2 and 16.5 in the 1996/1997 and 1997/1998, respectively, indicating greater stress the first season during vegetative growth. When deficit irrigation was increased to 8 weeks, DISI values were 34.1 and 39.8 for the respective seasons. Biomass production response to N in both years was quadratic; however, N response differed with irrigation level in both seasons. Highest biomass yield with no irrigation deficit was obtained at 120 kg N in 1996/1997 and at 160 kg N ha −1 in 1997. Nitrogen uptake was more dependent on applied N than water supply although N uptake decreased with greater water and N deficits. Water extraction was highest at the 120 and 160 kg N ha −1 rates with soil water deficit. This study showed that a maize crop differs in its ability to maintain LAI, CGR and above ground dry matter production at different levels of water deficit and N supply. The adaptive strategy of maize plants under vegetative water stress appears to be extended rooting depth and water extraction from the deeper soil profile, and simultaneous reduction in leaf area to decrease transpiration. Optimizing the inputs of water and N at the farm level would maximize biomass production and harvest index. This information can be useful to guide crop management strategy to enhance maize production in the irrigated perimeter of a Sahelian environment.

Adjustment procedures of a crop model to the site specific characteristics of soil and crop using remote sensing data assimilation

Crop models can be useful tools for estimating crop growth status and yield on large spatial domains if their parameters and initial conditions values can be known for each point. By coupling a radiative transfer model with the crop model (through a canopy structure variable like LAI), it is possible to assimilate, for each point of the spatial domain, remote sensing variables (like reflectance in the visible and near-infrared, or their combination into a vegetation index), and to re-estimate for this point some of the parameters or initial conditions of the model. The spatial adjustment of the crop model provides, therefore, a better estimation of yield. This process has been tested on the re-estimation of crop stand establishment parameters and initial conditions for sugar beet ( Beta vulgaris L.) crops, using the crop model SUCROS coupled to the radiative transfer model SAIL. The quality of recalibration depends in particular on the precision on the SAIL parameters other than LAI: soil reflectance, optical properties of leaves, and leaf angles. In applications on large domains, where these parameters may vary a lot, their estimation is an important factor in recalibration error. It was shown, using stochastic simulation, that beforehand knowledge of the variability of soil and crop characteristics considerably improved the results of the assimilation of reflectance measurements. The best results were obtained when the spectral reflectances were combined into the TSAVI vegetation index, which minimised the disruptive contribution of soil to the canopy reflectance. In particular, the use of TSAVI provided more consistent results for the estimates of the sowing date and emergence parameters, which remained poorer than yield estimates. Over a wide range of unknown crop situations corresponding to extreme sowing dates and emergence conditions, the proposed method allowed to estimate the sugar beet yield with relative errors varying from 0.6 to 2.6%. The results appeared to depend on the timing of remote sensing data acquisition; the best situation was when the data covered the whole period of LAI growth (including the highest values).

Effects of soil compaction on the relationships between nematodes, grass production and soil physical properties

As farm machinery has become heavier, concern has grown about its direct effects on soil physical conditions and its indirect effects on crop yields and soil biota. To study the relationships between these parameters, non-grazed temporary grassland plots on a loamy sand soil were subjected to full-width load traffic with widely different loads (0, 4.5, 8.5 and 14.5 t) one to four times per year for a period of 5 years. Soil bulk density was monitored as an indicator of soil compaction. Grass yield was measured throughout the experimental period. Root distribution over the soil profile and nematodes populations were assessed during the final year of the experiment. Results indicate that a moderate degree of compaction (∼4.5 t load) gave the highest crop yield and that at higher degrees of compaction roots failed to penetrate into the deeper soil layers (>20 cm depth). Total numbers of nematodes were not affected by compaction, but their distribution over the various feeding types shifted towards a population with increased numbers of herbivores and decreased numbers of bacterivores and omnivores/predators. This change in the structure of the nematode assemblage is associated with poorer conditions for crop growth.

Influences of degree of compactness and matric water tension on some important plant growth factors

The degree of compactness ( D) has been defined earlier as the dry bulk density of a soil in percent of a reference bulk density obtained by a standardized uniaxial compression test on large samples at a stress of 200 kPa. It was primarily aimed for use in annually disturbed soil layers. Field experiments have demonstrated its usefulness for characterizing the state of compactness from a crop production point of view, but knowledge is lacking regarding the relation between D and various plant growth factors. While the bulk density or porosity optimal for crop growth has varied considerably between soils, the optimal D-value has been virtually independent of soil texture. This led to a hypothesis that critical limits of penetration resistance (3 MPa) and air-filled porosity (10%, v/v) are similarly related to the D-value in most soils. With the objective to test this hypothesis, the positions of these limits as functions of the D-value and the matric water tension were studied in four soils with clay content ranging from 70 to 220 g kg −1. In all of them, the positions of the critical limits were similar. The higher the D-value, the more limited was the tension range offering adequate conditions for crop growth, the higher was the water tension (the lower the water content) at which aeration became critical, and the lower was the water tension (the higher the water content) at which penetration resistance became critical. The effects of critical soil conditions were reflected in increased stomatal resistance of plants grown in soil with a high D-value. The results provide basic information for modeling the relationships between soil compactness and plant growth.

Quantifying the growth and development of commercial barley cultivars over two contrasting growing seasons in Western Australia

The relationships between growth, development, and grain yield were examined in 3 phenologically different and commercially available barley cultivars over 2 growing seasons with very different weather patterns. Favourable conditions for crop growth in 1994 were followed by intensifying soil moisture stress over the second half of the season. In 1995, unfavourable conditions for crop growth due to saturated soils over the first half of the season were followed by favourable conditions and the growing season was extended by 1 month. Floral initiation was delayed, and the duration of the vegetative phase extended, when conditions were favourable for initial crop growth, but durations from sowing to anthesis and maturity were advanced when conditions for favourable crop growth were reversed. Differences in seasonal conditions over different portions of the growing seasons were reflected in corresponding differences in growth occurring over those periods. Favourable conditions up to the time of awn appearance in 1994 resulted in higher maximum leaf area indices than in 1995 (5.36 v. 2.59), higher shoot numbers per plant (10.2 v. 5.7), and higher dry mass per m2 (710 v. 462 g/m2). Favourable conditions after awn appearance in 1995 resulted in a higher proportional increase in dry mass over the grain development phase than in the previous year (57% v. 42%), higher grain numbers per spike (25 v. 23), greater grain size (41 v. 35 mg), and higher harvest indices (41% v. 38%). Final dry masses and grain yields, averaged over cultivars, did not differ significantly with season. Cultivars followed the same generalised patterns of growth and development, with opportunistic interactions between differences in the timing of developmental events and transient weather conditions determining the amountof, and rate with which, dry matter accumulated and the manner in which it was partitioned. Of the developmental differences recorded only one, the timing of awn appearance (= heading), was considered a useful selection criterion. The impact of transient and unpredictable variation in seasonal weather has major implications for the interpretation of studies not replicated over seasons and for early generation selection in barley breeding programs. A methodology for minimising the confounding influences involved is proposed.

Soil and residue management effects on arable cropping conditions and nitrous oxide fluxes under controlled traffic in Scotland: 1. Soil and crop responses

Soil compaction can affect crop growth and greenhouse gas emission and information is required of how both these aspects are affected by compaction intensity and weather. In this paper we describe treatments of compaction intensity and their effects on soil physical conditions and crop growth in loam to sandy loam cambisol soils. Soil conditions and crop performance were measured over three seasons in a field experiment on soil compacted by wheels on freshly ploughed seedbeds. Ploughing buried the chopped residues of the previous crop. After ploughing, traffic was controlled such that the experimental plots received wheel traffic only as treatments. The overall objective was to discover how the intensity and distribution of soil compaction just before sowing influenced crop performance, soil conditions and emissions of nitrous oxide. Compaction treatments were zero, light compaction by roller (up to 1 Mg m −1) and heavy compaction by loaded tractor, (up to 4.2 Mg). The experiment was located at Boghall, near Edinburgh (860 mm average annual rainfall) for the first two seasons under spring and winter barley ( Hordeum vulgare L.) and in a drier area at North Berwick (610 mm average annual rainfall) for the third season under winter oil-seed rape ( Brassica napus L.). Heavy compaction in dry soil conditions had little effect on crop growth. However, in wet conditions heavy compaction reduced air porosity, air permeability and gas diffusivity, increased cone resistance and limited winter barley growth and grain yield. Heavy compaction in wet conditions reduced winter barley yields to 7.1 Mg ha −1, in comparison to 8.8 Mg ha −1 in the zero compaction treatment. The compaction status of the top 15 cm of soil seemed to be particularly important. Loosening of the top 10 cm of soil immediately after heavy compaction restored soil conditions for crop growth. However, zero seed bed compaction gave patchy and uneven crop emergence in dry conditions. Both zero and light compaction to a target depth of 10 cm gave similar crop productivity. Maintenance of a correct compaction level near the soil surface is particularly important for establishment and overwintering of barley and oil seed rape.

Nitrate leaching affected by management options with respect to urine-affected areas and groundwater levels for grazed grassland

Simulations were performed to quantify the effects of management options on nitrate leaching to the groundwater in grazed pastures. At the experimental farm for sustainable dairy farming ‘De Marke’, experimental data on soil water and nitrates were gathered for two fields during the years 1991–1995. These data were used for model validation. The simulations showed that a detailed type of precision agriculture, which can identify urine-affected areas in the field and then subsequently omit fertilizing such areas, resulted in considerable reductions of simulated nitrate concentrations in the soil water, especially on an intensively grazed and relatively dry site with groundwater levels between 0.5 and 2.8 m. On the wetter site, the maximum calculated reduction in nitrate concentrations was 11%, but for the relatively dry site the maximum calculated reduction was as high as 41%. The second simulated option involved the raising of groundwater levels, which usually also resulted in a decrease in simulated nitrate concentrations. Under wet conditions, the groundwater level increase may cause water excess and a deterioration in conditions for crop growth and thus, less N-uptake by the crop, which would ultimately lead to increased nitrate leaching. The combined effect of non-fertilization of urine patches and the raising of groundwater levels usually resulted in higher simulated reductions of nitrate concentrations than the single options. When the effect of within-field variability was also considered, the raising of groundwater levels was most effective in reducing nitrate concentrations on the wet site, while on the relatively dry and intensively used site, the non-fertilization of urine-affected areas had the dominant effect. The study shows how simulation modelling can assist in identifying promising management strategies.

Soil structural quality, compaction and land management

SummarySoil compaction is a concern worldwide, particularly where compactible soils are used for intensive agriculture in a wet climate. We have investigated the impact of compaction and the associated changes in soil structural qualities on crop production and environmental pollution. The overall objective was to develop soil management systems that provide suitable conditions for crop growth and minimize environmental damage. We ran large‐scale field experiments studying the preservation of structural quality in arable and permanent grassland, using management systems such as the control or elimination of field traffic and the application of conservation tillage and zero tillage. We measured bulk density, shear strength, cone resistance, macroporosity, relative diffusivity, air permeability and water infiltrability to identify soil qualities that could be used for selecting suitable soil management. Along with crop yield, we measured environmental impacts, such as the emissions of nitrous oxide from the soil, which require the interaction of soil structure and water content near the soil surface. Soil structure influenced wetness, which affected trafficability, compaction and nitrogen retention. Measurement of properties that affect fluid storage and transport, such as macroporosity, provided soil quality indices that helped in recommending suitable soil management systems. Spatial variation of structure associated with wheel‐track locations could be estimated rapidly using a cone penetrometer. Variation was particularly important in determining crop yield consistency. Crop productivity and soil structural qualities were preserved best when field traffic was eliminated. A reduced ground‐pressure system successfully minimized compaction in grassland but was less effective in an arable rotation. Unless traffic is eliminated, good timing of operations is the most effective way to preserve soil structural quality.

The role of weed invasion in controlling sand dune reactivation in abandoned fields in semi‐arid Inner Mongolia, China

AbstractThe growth of crops and invading weeds were examined at six sites under different cultivation conditions in semi‐arid Inner Mongolia, where sand dune reactivation has been controlled by weed invasion. The soil moisture content was not sufficient for crop growth in over‐cultivated farmland. The shortage of moisture in the soil suppresses the growth of both crops and weeds. Accordingly, farmers carry out weeding to maintain better soil moisture conditions for crop growth. Over‐cultivated farmland is often abandoned when the crop yield decreases to an economically unprofitable level. If weed vegetation before abandonment remains, it becomes a core of vegetation expansion and recovers the entire soil surface. While weedy vegetation is lacking or has been grazed by livestock, sand dune reactivation occurs.

Do effects of soil compaction persist after ploughing? Results from 21 long-term field experiments in Sweden

The extent and persistence of the effect of soil compaction in a system with annual ploughing were investigated in 21 long-term field experiments in Sweden with a total of 259 location-years. Crop yield, soil physical properties and plant establishment were determined. All experiments had two common treatments: control (no extra traffic) and compacted (350 Mg km ha −1 of experimental traffic in the autumn prior to ploughing), using a tractor and trailer with traditional wheel equipment and an axle load restricted to 4 Mg. During the rest of the year, both treatments were conventionally and equally tilled. The compaction was repeated each autumn for at least 7 years, and the yield was determined each year until 5 years after the termination of the compaction treatment. Compaction decreased the porosity and the proportion of large pores and increased the tensile strength of dry aggregates. On clay and loam soils, it decreased the proportion of fine aggregates in the seedbed and the gravimetric soil water content in the seedbed. The yield in the compacted treatment declined compared with the control during the first 4 years, after which it reached steady state. During this steady state, the compaction treatment caused a yield loss of 11.4%, averaged over 107 location-years. Within 4–5 years after the termination of the compaction treatment, the yield returned to the control level. The average yield loss at individual sites increased with increasing clay content. Results from additional treatments indicated that yield loss was linearly correlated with the amount of traffic up to 300–400 Mg km ha −1. With greater ground contact pressure or a greater soil water content at time of traffic, there was a greater yield loss. Soil compaction effects on yield were similar for all spring-sown crops, and the percentage yield loss seemed to be independent of the yield. In a few location-years with winter wheat there was on average no yield decrease. There were 5.1% less plants in the compacted treatment than in the control. The yield decrease was significantly correlated with the number of plants. Between years results were highly variable, and no consistent correlations between yield loss and soil water content at the time of traffic or the weather conditions during the growing period were found. Soil compaction affected yield during years with good as well as poor conditions for crop growth.

Diagnosis of regional evaporation by remote sensing to support irrigation performance assessment

The success of water management in large irrigation schemes with composites of soil, crop, wetness and micro-meteorological conditions is difficult to quantify. Performance assessment indicators, being among others a function of evaporation, are useful tools to evaluate the actual functioning of an irrigation system. The inevitable spatial variability of evaporation in large irrigation schemes makes its determination with conventional point measurements almost impossible. A new remote sensing evaporation parameterization algorithm has been tested with high resolution Landsat Thematic Mapper data for the Eastern Nile Delta, Egypt. Although the implementation of such an algorithm requires assumptions to be made, the current case study shows that these assumptions do not hamper the estimation of actual and potential evaporation at regional scale. The actual evaporation has been used to express the uniformity of crop water use which is related to the equity of irrigation water distribution. The coefficient of variance in actual evaporation between 53 differenent irrigation districts is 10% on average. The relative evaporation was considered to determine whether the crop was adequately irrigated. The relative evaporation was more than 75% for 48 out of 53 irrigation districts. It is concluded, that improved information on actual crop growth conditions through remote sensing provides an essential insight into the planning of real-time and seasonal irrigation water deliveries.

Developing and Validating a Model for a Plant Growth Regulator

AbstractMepiquat chloride (MC), 1,1‐dimethylpiperidinium chloride, is a systemic plant growth regulator used extensively to regulate vegetative growth in cotton (Gossypium hirsutum L. and G. barbadense L.). Yield responses to MC have been erratic, probably due to the difficulty in choosing the proper rate and timing of application. We developed a model based on data collected by spraying various amounts of MC on 25‐d‐old plants. The effect of MC on various physiological parameters was measured. Stem elongation rate was reduced 38% due to 30 µg g−1 of MC, while leaf area expansion rate and photosynthesis was reduced 30%. The model adjusts the projected leaf expansion, stem elongation, and photosynthetic rates based on the crop growth status and concentrations of MC in the tissues. The MC subroutine was incorporated into GOSSYM‐COMAX, a combined simulation model for plant growth and decision aid for cotton crop management. We tested the model against data for plant heights, mainstem nodes, and yields from several cropping systems across the U.S. Cotton Belt. The simulation results agreed closely with the observed field data. The new model reduced the overall variability 32% for predicting plant heights, 4% for predicting number of mainstem nodes, and 17% for predicting lint yields over the previously published MC model. When used in association with GOSSYM‐COMAX, the MC model may provide an effective tool for selecting precise timing and amounts of mepiquat chloride needed to optimize the proper use of the chemical.

Nitrate-N, ammonium-N, and organic matter in relation to profile characteristics of Dark Brown Chernozemic soils

Thirty-six deep soil profiles (3.3 m) from a 32-ha irrigated field in southern Alberta were evaluated to determine the relationship between pedogenic development and nitrate-nitrogen (NO3-N), ammonium-nitrogen (NH4-N), and organic matter (OM) content and distribution. The soils were classified into three fine-loamy Dark Brown subgroups. Three classes of solum thickness and slope position were identified. The NO3-N, NH4-N, and OM content in the 3.3-m profile, and below the solum, the control section, and the 1.2-m rooting depth were compared and correlation analyses were conducted between these properties and properties of the saturation extract.The OM content decreased exponentially with increase in profile depth, but the NO3-N and, to some extent, the NH4-N contents varied according to solum thickness regardless of subgroup classification. On average, soils with a thin (< 35 cm) or thick (> 75 cm) solum had a zone of high NO3-N concentration between the 100- and 150-cm depths. This was ascribed to less favorable soil moisture conditions for crop growth on the thin-solum soils and probably more frequent leaching events in the thick-solum soils. Distinctly different correlation coefficients between NO3-N, NH4-N, and OM and the saturation extract properties of the control section supported the series designations of the solum-thickness separations. Solum thickness and topographic position should be considered when applying nitrogen fertilizers or irrigations. Key words: Semiarid region, intermittent irrigation, Chernozemic soils, nitrate-N, ammonium-N, organic matter

Structural and hydrological changes in a Vertisol under different fallow management techniques

Retention of crop residues (stubble) and zero (or no) tillage are accepted fallow management techniques for reducing erosion of Vertisols in northeastern Australia. However, on some Vertisols these techniques give adverse soil conditions for crop growth. The effect of different fallow management techniques on soil physical properties of one of these soils was investigated. Soil structural and hydrologic properties were determined under three tillage and two stubble fallow management treatments. Measurements were made immediately prior to planting a crop, and some were repeated after harvest. Zero tillage increased bulk density, shear strength, penetrometer resistance and aggregate size (as did stubble retention) at planting, compared with blade or disc plough tillage. These results indicate that seedbed conditions were less favourable for crop establishment under this treatment. Sorptivity, steady-state infiltration rate and curve number values, determined from infiltration of simulated rainfall, were lower in zero tillage treatments, especially where stubble was removed. Infiltration parameters determined with ponded rings and well permeameters were not as sensitive to treatments. Soil moisture characteristics were significantly affected by tillage, with the blade treatment retaining more water at all suctions. Infiltration results were consistent with previous measurements of soil water storage in stubble removed and zero tilled treatments. Macropores (soil cracks or insect and earthworm burrows) were important in infiltration of simulated rain. From the results of this experiment, the favoured fallow management practice for crop production and erosion control in this soil is blade plough tillage with stubble retained.

The effects of nitrate: ammonium ratios and dicyandiamide on the nitrogen response of Zea mays L. in a high rainfall area on an acid soil

Hydroponic studies under controlled environmental conditions indicated that maize plants respond better to combinations of nitrate and ammonium nutrition than to either form supplied separately but that this response depended upon the total N concentration. An attempt was made to maintain different nitrate: ammonium ratios and concentrations in the soil by the addition of a nitrification inhibitor. Five nitrate: ammonium ratios at three N application rates were tested with and without dicyandiamide (H2NC(NH)NHCN) on a low-pH, sandy soil for two years. Treatments were applied to field-grown maize in two applications, one at planting and the other at 21 to 30 days after planting. Under favourable climatic conditions for crop growth the optimum nitrate: ammonium ratio for grain yield was between 3:1 and 1:1 over all N rates. Under unfavourable climatic conditions, ratios of 3:1 and 1:1 showed in contrast to all other ratios no grain yield depressions at high N rates. Dicyandiamide did not interact with N rates or ratios, but did increase grain yield over all N treatments under favourable conditions. N ratio interactions with N rates and dicyandiamide were also shown for N concentrations of the leaves at anthesis, for the grain at harvest and for mineral N in different soil layers at anthesis. These results imply that nitrate: ammonium ratios between 3:1 and 1:1 should be recommended at the optimum N rate on a low-pH sandy soil in a high rainfall area for maize production.

Structure and function of a computer system for soil diagnosis

Abstract The author has developed a soil diagnosis system utilizing a personal computer. This system enables to prepare data files for soil profile, soil physical and chemical properties, and also, as required, for the columnar section of a soil profile, three-phase distribution, pF-soil moisture curve, diagnosis, and recommendations, radar chart, etc. As a result, soils can be comprehensively diagnosed and the results can be used for recommending to the farmers appropriate methods of soil improvement and fertilizer application. Moreover, a field management system as subsystem can be developed to determine the field management and crop growing conditions in the area when the soil diagnosis was performed. Location of the survey spot was stored in an image file by using a large-scale map, in which subdivisions could be identified, and was registered using X. Y coordinates on a computer display screen. Through the utilization of this farm map, the soil characteristics and their relation with the growth of cr...