Irrigated Grain Research Articles

Can Cover Crop Use Allow Increased Levels of Corn Residue Removal for Biofuel in Irrigated and Rainfed Systems?

Corn (Zea mays L.) residue removal at high rates can result in negative impacts to soil ecosystem services. The use of cover crops could be a potential strategy to ameliorate any adverse effects of residue removal while allowing greater removal levels. Hence, the objective of this study was to determine changes in water erosion potential, soil organic C (SOC) and total N concentration, and crop yields under early- and late-terminated cover crop (CC) combined with five levels of corn residue removal after 3 years on rainfed and irrigated no-till continuous corn in Nebraska. Treatments were no CC, early- and late-terminated winter rye (Secale cereale L.) CC, and 0, 25, 50, 75, and 100% corn residue removal rates. Complete residue removal reduced mean weight diameter (MWD) of water-stable aggregates (5 cm depth) by 29% compared to no removal at the rainfed site only, suggesting increased water erosion risk at rainfed sites. Late-terminated CC significantly increased MWD of water-stable aggregates by 27 to 37% at both sites compared to no CC, but early-terminated CC had no effect. The increased MWD with late-terminated CC suggests that CC when terminated late can offset residue removal-induced risks of water erosion. Residue removal and CC did not affect SOC and total soil N concentration. Particulate organic matter increased with late-terminated CC at the irrigated site compared to no CC. Complete residue removal increased irrigated grain yield by 9% in 1 year relative to no removal. Late-terminated CC had no effect on corn yield except in 1 year when yield was 8% lower relative to no CC due to low precipitation at corn establishment. Overall, late-terminated CC ameliorates residue removal-induced increases in water erosion potential and could allow greater levels of removal without reducing corn yields in most years, in the short term, under the conditions of this study.

Heat stress is overestimated in climate impact studies for irrigated agriculture

Climate change will increase the number and severity of heat waves, and is expected to negatively affect crop yields. Here we show for wheat and maize across Europe that heat stress is considerably reduced by irrigation due to surface cooling for both current and projected future climate. We demonstrate that crop heat stress impact assessments should be based on canopy temperature because simulations with air temperatures measured at standard weather stations cannot reproduce differences in crop heat stress between irrigated and rainfed conditions. Crop heat stress was overestimated on irrigated land when air temperature was used with errors becoming larger with projected climate change. Corresponding errors in mean crop yield calculated across Europe for baseline climate 1984–2013 of 0.2 Mg yr−1 (2%) and 0.6 Mg yr−1 (5%) for irrigated winter wheat and irrigated grain maize, respectively, would increase to up to 1.5 Mg yr−1 (16%) for irrigated winter wheat and 4.1 Mg yr−1 (39%) for irrigated grain maize, depending on the climate change projection/GCM combination considered. We conclude that climate change impact assessments for crop heat stress need to account explicitly for the impact of irrigation.

Examining the impacts of increased corn production on groundwater quality using a coupled modeling system.

This study demonstrates the value of a coupled chemical transport modeling system for investigating groundwater nitrate contamination responses associated with nitrogen (N) fertilizer application and increased corn production. The coupled Community Multiscale Air Quality Bidirectional and Environmental Policy Integrated Climate modeling system incorporates agricultural management practices and N exchange processes between the soil and atmosphere to estimate levels of N that may volatilize into the atmosphere, re-deposit, and seep or flow into surface and groundwater. Simulated values from this modeling system were used in a land-use regression model to examine associations between groundwater nitrate-N measurements and a suite of factors related to N fertilizer and groundwater nitrate contamination. Multi-variable modeling analysis revealed that the N-fertilizer rate (versus total) applied to irrigated (versus rainfed) grain corn (versus other crops) was the strongest N-related predictor variable of groundwater nitrate-N concentrations. Application of this multi-variable model considered groundwater nitrate-N concentration responses under two corn production scenarios. Findings suggest that increased corn production between 2002 and 2022 could result in 56% to 79% increase in areas vulnerable to groundwater nitrate-N concentrations ≥ 5 mg/L. These above-threshold areas occur on soils with a hydraulic conductivity 13% higher than the rest of the domain. Additionally, the average number of animal feeding operations (AFOs) for these areas was nearly 5 times higher, and the mean N-fertilizer rate was 4 times higher. Finally, we found that areas prone to high groundwater nitrate-N concentrations attributable to the expansion scenario did not occur in new grid cells of irrigated grain-corn croplands, but were clustered around areas of existing corn crops. This application demonstrates the value of the coupled modeling system in developing spatially refined multi-variable models to provide information for geographic locations lacking complete observational data; and in projecting possible groundwater nitrate-N concentration outcomes under alternative future crop production scenarios.

English

Livestock is more important to the Mauritanian economy (13% of National Gross Domestic Product) compared with just 4% from crop production. It is surprising, therefore, that irrigation has so far contributed little to animal productivity given the limited carrying capacity and irregular inter-annual production of the extensive rangeland, and the need to import fodder concentrates to sustain livestock during the hot-dry season (April to June). Our hypothesis is that growing irrigated sorghum and cowpea planted late in the mild-dry season (December-January after rice harvest (November-December) would improve profitability and sustainability of irrigation schemes. The objective is to replace fodder concentrates, currently purchased abroad, by fodder grown in irrigation schemes. To test our hypothesis we performed an extensive survey of 12 villages located within a significant gradient of rainfall from West to South-East along the northern bank of the Senegal River and used a simulation model constructed to study interactions between traditional and irrigated grain and/or fodder crop. The results of this study reveal how the introduction of irrigated sorghum and cowpea sown late in the mild-dry season would, even at relatively moderate yields (2.8-4.1 and 1.4-2.1 t grain ha-1, for sorghum and cowpea, respectively), provide additional grain required by smallholder farmers and reduce costs of livestock production (30%). In addition, the introduction of these crops increases by 31­ to 54% the household net agricultural production of households having only small ruminants and by 14 to 23% of households having both small ruminants and cattle. Extending the irrigated cropping season shares the depreciation costs over more crops and improves the sustainability of the irrigation schemes. The regions that would most benefit from these additional irrigated crops are Trarza and Gorgol where the demand and hence prices of sorghum and cowpea grain and fodder are higher than in the other regions. Key words: Mauritania, livestock, irrigated rice, irrigated sorghum, irrigated cowpea, household net agricultural production.

Modelo agrometeorológico-espectral para estimativa da produtividade de grãos de arroz irrigado no Rio Grande do Sul

RESUMO O objetivo deste trabalho foi elaborar e testar um modelo agrometeorológico-espectral para a estimativa da produtividade de grãos de arroz irrigado para o Estado do Rio Grande do Sul. Para as seis regiões orizícolas do Estado, foram utilizados dados de área cultivada e rendimento de grãos de arroz irrigado, dados meteorológicos e imagens do Índice de Vegetação por Diferença Normalizada (NDVI) do sensor Moderate Resolution Imaging Spectroradiometer (MODIS), de agosto a abril, para as safras de 2000/2001 até 2009/2010. A temperatura mínima do ar e o NDVI estão associados ao rendimento de grãos de arroz irrigado em diversos períodos do desenvolvimento da cultura. O modelo agrometeorológico-espectral para estimativa de produtividade de grãos, ajustado através da abordagem orientada pelas relações clima-planta, é adequado às estimativas em nível regional, podendo fornecer estas com cerca de um mês de antecedência ao final da colheita.

Nitrogen and Phosphorus Fertilization of Irrigated Grain Sorghum

Abstract only. Link to: http://newprairiepress.org/kaesrr/vol1/iss3/6/) Article is nearly identical to Long-Term Nitrogen and Phosphorus Fertilization of Irrigated Grain Sorghum, previously published in Kansas Fertilizer Research 2015, included in this PDF. Long-term research shows that phosphorus (P) and nitrogen (N) fertilizer must be applied to optimize production of irrigated grain sorghum in western Kansas. In 2014, N applied alone increased yields 49 bu/a, whereas N and P applied together increased yields up to 81 bu/a. Averaged across the past 10 years, N and P fertilization increased sorghum yields up to 73 bu/a. Application of 40 lb/a N (with P) was sufficient to produce more than 80% of maximum yield in 2014, which almost equals the 10-year average. Application of potassium (K) has had no effect on sorghum yield throughout the study period.

Long-Term Nitrogen and Phosphorus Fertilization of Irrigated Grain Sorghum

Long-term research shows that phosphorus (P) and nitrogen (N) fertilizer must be applied to optimize production of irrigated grain sorghum in western Kansas. In 2014, N applied alone increased yields 49 bu/a, whereas N and P applied together increased yields up to 81 bu/a. Averaged across the past 10 years, N and P fertilization increased sorghum yields up to 73 bu/a. Application of 40 lb/a N (with P) was sufficient to produce more than 80% of maximum yield in 2014, which almost equals the 10-year average. Application of potassium (K) has had no effect on sorghum yield throughout the study period.

Incidental Aquaculture in California's Rice Paddies: Red Swamp Crawfish

Introduction of the red swamp crawfish, Procambarus clarkii, into California and its diffusion throughout northern California's rice paddies created the conditions for an incidental aquaculture economy in a landscape devoted to irrigated grain production. For more than three decades, fishermen have harvested this prolific invader and sold their catch to Europe and the Gulf Coast. Since 2004, the diffusion of Vietnamese‐American seafood restaurants to California and nationally has created additional markets for red swamp crawfish.

Estimation of Agricultural Water Consumption from Meteorological and Yield Data: A Case Study of Hebei, North China

Over-exploitation of groundwater resources for irrigated grain production in Hebei province threatens national grain food security. The objective of this study was to quantify agricultural water consumption (AWC) and irrigation water consumption in this region. A methodology to estimate AWC was developed based on Penman-Monteith method using meteorological station data (1984–2008) and existing actual ET (2002–2008) data which estimated from MODIS satellite data through a remote sensing ET model. The validation of the model using the experimental plots (50 m2) data observed from the Luancheng Agro-ecosystem Experimental Station, Chinese Academy of Sciences, showed the average deviation of the model was −3.7% for non-rainfed plots. The total AWC and irrigation water (mainly groundwater) consumption for Hebei province from 1984–2008 were then estimated as 864 km3 and 139 km3, respectively. In addition, we found the AWC has significantly increased during the past 25 years except for a few counties located in mountainous regions. Estimations of net groundwater consumption for grain food production within the plain area of Hebei province in the past 25 years accounted for 113 km3 which could cause average groundwater decrease of 7.4 m over the plain. The integration of meteorological and satellite data allows us to extend estimation of actual ET beyond the record available from satellite data, and the approach could be applicable in other regions globally where similar data are available.

Grain Yield and Plant Characteristics of Corn Hybrids in the Great Plains

Water supply for crop use is the primary factor controlling corn (Zea mays L.) grain yield in the west‐central Great Plains. With water supply varying as production systems range from dryland through irrigated, selecting hybrids for optimum yield in the anticipated water environment is vital for success. Our objective was to analyze a group of corn hybrids and determine: (i) if there are significant differences in identifiable plant characteristics among the hybrids and (ii) if there are significant associations between identifiable plant characteristics and grain yield. Corn was grown near Tribune, KS, for 3 yr in two fields, one dryland and one irrigated. Hybrids (18) replicated in four blocks were grown in each field, with dryland and irrigated results analyzed separately. From linear regression, no significant correlation existed between irrigated grain yield and days to initial silking of hybrids in any of the 3 yr. The correlation between dryland grain yield and days to initial silking of hybrids was significant (P < 0.05) in all 3 yr, with grain yield decreasing as days to initial silking increased. Dryland grain yield was also significantly and negatively correlated with dry stover mass in all 3 yr and with tiller population in 2 of 3 yr. Hybrids selected for dryland conditions in the west‐central Great Plains should be from the earlier third or half of the 98‐ to 118‐d relative maturity range of our study. In addition, hybrids selected for dryland conditions should have characteristics of smaller stature (less stover) and nontillering plants.

Physical land suitability evaluation for specific cereal crops using GIS at Mashhad Plain, Northeast of Iran

Land evaluation is the process of predicting land use potential on the basis of its attributes. In the present study, the physical land suitability evaluation approach was investigated for specific cereal crops including irrigated wheat, barley, grain maize and sorghum, based on FAO land evaluation frameworks (FAO, 1976, 1983, 1985) and the proposed method by Sys et al. (1991) at Mashhad Plain, Northeast Iran. Twenty eight soil profiles were studied on seven land units by a precise soil survey and their morphological and physicochemical properties were determined. Climatic and land qualities/characteristics of four cereal crops were determined using the tables of crop requirements developed by Sys et al. (1993). An interpolation function was used to map values to scores in terms of land qualities/characteristics for land utilization types and the evaluation was carried out according to parametric approaches. The interpolation technique using GIS functions helped in managing the spatial data and visualizing the results. Our results indicated that the most important limiting factors for irrigated wheat and barley cultivations are soil physical and fertility/chemical properties, while the production of irrigated grain maize and sorghum is mainly limited by climatic conditions at Mashhad Plain. It was shown that all land units suitable for irrigated wheat cultivation overlap with that of barley, whereas the same limiting factors resulted in the overlapping of the irrigated grain maize production area with that of sorghum. The results of the physical land suitability evaluation for specific cereal crops indicated the priority of irrigated barley and wheat cultivations over irrigated grain maize and sorghum at the study area.

Crop protection in European maize-based cropping systems: Current practices and recommendations for innovative Integrated Pest Management

Maize-based cropping systems (MBCSs), with different frequency of maize in the crop sequence, are common in European arable systems. Pesticide use differs according to the type of active ingredients and target organisms in different regions. Within the EU Network of Excellence ENDURE, two expert-based surveys were conducted focusing on four European study regions where experts were asked to identify MBCSs in their region, determine the current crop protection practices, propose advanced practices against major pests, weeds and diseases, and evaluate the potential agronomic, environmental, economic and social impact of innovative Integrated Pest Management (IPM) tools on the sustainability of MBCSs. In the northern region (Denmark and The Netherlands), maize is mostly cultivated as non-irrigated continuous silage maize or rotated with grass, while in the central-eastern region the major systems are non-irrigated continuous grain maize (Tolna county, Hungary) or grain maize grown in rotation with winter wheat, oilseed rape and sunflower (Békés county, Hungary). In the south-western (Ebro Valley, Spain) and southern (Po Valley, Italy) regions, continuous and irrigated grain maize, as well as irrigated grain and silage maize/winter wheat rotations are prevalent. Differences in current and proposed advanced crop protection practices for MBCSs were identified between regions due to specific pest, weed and disease problems. The tolerant/resistant non-GM maize cultivars, early detection methods, pest and disease forecasting models, precision/patch spraying using GPS spray maps and the community-based decisions through information sharing were commonly recommended for innovative IPM implementation in all regions. Deviations in the recommendations between regions were mainly caused by differences in the evaluation of economic or social impact of some tools (i.e. innovative mechanical weeding). Applied multi-disciplinary research and farmer incentives to encourage the adoption of innovative IPM strategies are essential for sustainable MBCSs development in Europe. The introduction of innovative tools into IPM strategies can contribute significantly to addressing the EU’s strategic commitment to the sustainable use of pesticides and, consequently, more environmentally sustainable MBCSs.

Response of different corn populations to fertigated nitrogen and certain micronutrients in sandy soil

A field study was conducted during 2008 and 2009 at El-Khattara farm station, Zagazig Uni-versity, Sharkyia, Egypt (30°36' N, 32°15' E) to determine the effect of three N rates (214, 273, and 333 kg N ha-1), four micronutrients spray treatments (Check, Zn, Mn, and Zn + Mn), and three planting density levels ( 4.76, 5.71, and 6.66 plant m-2) on growth and grain yield of corn (Zea mays, L). The soil was sandy (Entisols) and groundwater was used for irrigation. Response to N was maximized to 214 kg ha-1 without a significant effect on most growth traits and grain yield. Agronomic efficiency of N use for grain yield was negatively related to N rate (r2 = 0.49). Application of micronutrients had no ef-fect on most growth and yield characters except a significant increase by 9.5, 8.7, and 9 % in plant weight (g plant-1), biomass yield (kg m-2), and N agronomic efficiency for biomass yield, respectively. Growth was decreased by in-creasing plant density without affecting harvest index, agronomic efficiency, biomass yield, and grain yield. The application of Zn to the highest maize plant density increased grain yield by 16 % as compared to the check. It is recommended, as predicated by the linear model, that N ferti-gation rate should be around 220 kg ha-1 with plant density of 6.66 plant m-2 accompanied by Zn application for maximum irrigated corn grain yield in sandy soil. Abbreviations: DAS, days after sowing; LA, leaf area; LAI, leaf area index; RPP, relative photosynthetic potential; HI, har-vest index; BW, plant weight g plant-1, GYP, grain yield g plant-1, BYM, biomass yield kg m-2, GYM, grain yield kg m-2, NAE, nitrogen agro-nomic efficiency.

Effect of selenium fertiliser formulation and rate of application on selenium concentrations in irrigated and dryland wheat (Triticum aestivum)

Field trials were carried out on two wheat (Triticum aestivum) crops (one irrigated, one dryland) in Canterbury, New Zealand during the 2005–06 growing season to evaluate the effectiveness of two selenium (Se) fertilisers in raising grain Se levels. Both contained sodium selenate: “AgSel” is a fast release formulation (100% water‐soluble Se) whereas “Selprill Double” (76% water‐soluble Se) has been formulated to slow the release of Se. The fertilisers were broadcast in spring (Zadoks growth stage 32) at rates of 5 to 20 g Se/ ha. Grain Se increased linearly with application rate, but concentrations were higher with the fully‐soluble formulation. Mean Se concentration was significantly lower in irrigated (grain yield 9.1 t/ha) than dryland (yield 7.4 t/ha) wheat (0.17 versus 0.25 mg Se/kg), possibly owing to yield dilution. For the fully‐soluble Se fertiliser, grain Se increased by 0.018 mg/kg in irrigated wheat for each g/ha of applied Se. an application of 4–5 g/ha would raise grain Se to 0.1 mg/kg (approximate concentration in imported australian wheat), assuming natural levels in Canterbury wheat are c. 0.02 mg/kg. The water‐insoluble component of Selprill Double made little or no contribution to Se uptake when the fertiliser was applied in spring and therefore application rates should be c. 30% higher than those of the fully‐soluble fertiliser.

Paper submitted for the nineth international drainage workshop (ICID)

The environmental benefits of water table management (WTM), as a method to reduce nitrate pollution, are well known. However, there are few published studies on the effects of WTM on water use efficiency (WUE). This paper highlights the agronomic interest of WTM for increasing WUE of irrigated grain corn production. A field study was conducted in 2001 and 2002 at a large scale WTM research facility in Quebec, Canada. The region experienced periods of drought during the two growing seasons. This study shows that, by keeping the water table at 0.80 m below the soil surface, there were on average 35% increases in grain corn yields, compared to conventional free drainage. The WUEs obtained with WTM (5.1 kg m−3 in 2001 and 7.1 kg m−3 in 2002) indicate that the method is generally more water efficient than conventional sprinkler and furrow irrigation. The WUE of WTM also compares well with that of water conservation methods such as alternate furrow irrigation and deficit sprinkler irrigation. Moreover, WTM requires low inputs in terms of equipment, energy, and labour, because it makes use of existing subsurface drainage systems, which are widespread in Eastern Canada due to the region's soils and climate, and because of its design, which does not necessitate high-pressure pumps and allows for automated management. Hence, WTM appears to be an interesting alternative to conventional irrigation methods due to its combined environmental and agronomical benefits.

Spatial and temporal variability of corn grain yield: site-specific relationships of biotic and abiotic factors.

Inadequate information on factors affecting crop yield variability has contributed to the slow adoption of site-specific farming (SSF). This study was conducted to determine the effects of biotic and abiotic factors on the spatial and temporal variability of irrigated corn grain yields and to derive information useful for SSF. The effects of water (80% evapotranspiration (ET) and 50% ET), hybrid (drought-tolerant and -susceptible), elevation, soil index (SI)(texture), soil NO3–N, arthropods, and diseases on corn grain yield were investigated at Halfway, TX on geo-referenced locations. Grain yields were influenced by interrelationships among biotic and abiotic factors. Grain yields were consistently high under high water treatment, at higher elevations, and on soils with high SI (high clay and silt). Soil NO3–N increased grain yields when water was adequate. Management zones for variable rate fertilizer and water application should, therefore, be based on information on elevation, SI, and soil NO3–N. The effects of arthropods, diseases, and crop stress (due to drought and N) on corn grain yield were unpredictable. Spider mite (Oligonychus pratensis) and common smut (Ustilago zeae) damage occurred under hot and dry conditions in 1998. Spider mite infestations were high in areas with high soil NO3–N. Moderate air temperatures and high relative humidity in 1999 favored southwestern corn borer (Diatraea grandiosella) and common rust (Puccinia maydis) incidences. Knowledge of conditions that favor arthropods and diseases outbreak and crop stress can improve the efficiency of scouting and in-season management of SSF. Management of SSF can be improved when effects of biotic and abiotic factors on grain yield are integrated and evaluated as a system.

Tillage Effects on Grain Sorghum and Wheat Yields in the Texas Rolling Plains

AbstractSoils of the Texas Rolling Plains have poor structure, low soil organic matter contents, and low water holding capacity. Alternative farming practices must be explored to conserve and improve this natural resource. An 11‐yr (1979‐1989) field experiment was conducted at the Texas A&M University Research Station at Munday to determine the effects of tillage (reduced vs. conventional) and residue management (with vs. without residue) on grain yields of continuous grain sorghum [Sorghum bicolor (L.) Moench] and continuous wheat (Triticum aestivum L.) under dryland and irrigated conditions. A grain sorghum—wheat rotation (double‐crop) under reduced tillage was included in the irrigated study. Yields of reduced‐tillage grain sorghum in dryland and irrigated studies were as high or higher than yields of conventional‐tillage grain sorghum. Removal of surface residues in irrigated grain sorghum caused a significant decrease in yields. In contrast, reduced‐tillage systems and surface residues caused reductions in yields for dryland and irrigated wheat, which may be the result of decreased plant populations caused by poor seed‐to‐soil contact when planting through surface residues and N deficiency caused by immobilization. The average yield of irrigated wheat or grain sorghum using reduced‐tillage double‐cropping (2 and 3 Mg ha−1, respectively) was lower relative to wheat (3.5 Mg ha−1) and grain sorghum (4.6 Mg ha−1) grown continuously under conventional tillage.

AGRICULTURE: An Often-Overlooked Opportunity For Energy Conservation

One of the most important agricultural regions in the US is the Panhandle region, the Southern region of America`s Great Plains. In recent years, there has been renewed interest in agricultural energy efficiency in the Panhandle region which covers Eastern New Mexico, Texas Panhandle, and Oklahoma Panhandle. The declining prices for agricultural products has prompted local farmers and agribusinesses to control costs so as to maintain profitability. In the Panhandle region, electricity is provided primarily by Southwestern Public Service (SPS) Company. Four different types of agricultural activities or establishments--irrigation pumping, feed lots, grain elevators, and cotton gins--account for over three-quarters of SPS`s retail sales of electricity to the agricultural sector. Although the focus of this article is to explore cost-effective energy-efficiency opportunities in the Panhandle agricultural sector, most of the measures can be applied to other agricultural regions in the US. Specific energy efficiency measures are identified and potential energy savings are quantified.

Economic Feasibility of Using Composted Manure on Irrigated Grain Sorghum

The economic feasibility of using composted manure from western Kansas feedlots in combination with commercial N in the production of irrigated grain sorghum [Sorghum bicolor (L.) Moench] was evaluated. Effective disposal of large quantities of manure from large scale feedlots has been a concern. Yield data from a west central Kansas experiment station study was used to estimate a quadratic production function where grain sorghum yield is a function of compost and commercial N application rates. Four rates of commercial N (0, 55, 110, and 165 Ib/acre) and five rates of composted feedlot manure (0, 0.9, 1.8, 3.6, and 7.2 tons dry matter per acre) in a factorial arrangement were applied to irrigated grain sorghum [...]

Residual effects of irrigated soybean on the growth and yield of irrigated grain sorghum

Irrigated grain sorghum was cropped immediately following irrigated soybean, to establish whether there were any residual effects on sorghum from the previous management of soybean. Results of experiment 1 showed that, where soybean residues were incorporated, sorghum DM accumulation and grain yields were greatest where soybean had been least frequently irrigated (after about 240 mm cumulative open pan evaporation), and least where the soybean had been grown with saturated soil culture (SSC). Extractable mineral nitrogen (N) at sowing of the sorghum was also least following the SSC soybean and greatest following the least-frequently irrigated soybean. The subsequent availability of N during sorghum growth appeared greater where the soybean was more frequently irrigated, although the release occurred too late to influence grain yield. In experiments 2 and 3 residual effects of conventional irrigation of soybean after 60 mm evaporation were compared with those of SSC. Where soybean stubble was uniformly removed (experiment 2), no significant effects of previous irrigation were observed. Where soybean stubble was either removed or incorporated (experiment 3), sorghum yields were lower following the SSC soybean. The incorporation of soybean stubble delayed the release of soil N, although this was not reflected in lower sorghum yields. Taken together, the studies suggested that, for a sorghum crop following soybean, more N fertiliser will be needed at sowing where the soybean stubble is incorporated; where the soybean had been well-irrigated; and the sooner after soybean harvest the sorghum is sown. Conversely, there were indications that more N may be available late in the growth of the sorghum crop where soybean had been well irrigated.