Irrigated Cropping Systems Research Articles

Trends and Implications of Genotype by Environment Interaction in South African Sugarcane Breeding

Genotype by environment interaction (GxE) influences and complicates the selection of superior genotypes in trials by confounding the determination of true genetic values. In South Africa, variety trials are planted at several locations and harvested in the plant to third ratoon crops. The objective of this study was to determine the trends in components of GxE and their implications. The MIXED procedure of Statistical Analysis System (SAS) was used to estimate variance components. Genotype by location interaction was significant for the irrigated and coastal long-cycle programs, indicating the importance of identifying and characterizing sites. Genotype by crop-year interaction was larger and more significant for rain-fed than for irrigated cropping system, indicating the importance of ratooning ability in rain-fed regions. Genotype by location by crop-year interaction was significant (P < 0.01) for yield and sucrose content, highlighting the complexity associated with breeding sugarcane. The coastal long-cycle program was the most complex and generally characterized by large GxE. Separating the coastal hinterland and coastal average potential would be recommended to reduce GxE.

Corrigendum to &amp;quot;Responses of N&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;O and CH&amp;lt;sub&amp;gt;4&amp;lt;/sub&amp;gt; fluxes to fertilizer nitrogen addition rates in an irrigated wheat-maize cropping system in northern China&amp;quot; published in Biogeosciences, 9, 839–850, 2012

f(x) = 76.41‐34.21· 0.997x 0.98 < 0.01 Fig. 3a Wheat: f(x) = 8.03‐1.74· 0.996 x 0.90 < 0.01 Fig. 3b Wheat straw: f(x) = 5.49 + 0.002·x 0.79 < 0.05 Maize: f(x) = 9.16‐4.24· 0.997x 0.96 < 0.01 Wheat grain: f(x) = 21.15 + 0.005·x 0.74 < 0.05 Wheat + Maize: f(x) = 16.51‐5.36· 0.996 x 0.95 < 0.01 Maize straw: f(x) = 8.03 + 0.009·x 0.80 < 0.05 Maize grain: f(x) = 12.51 + 0.004·x 0.90 < 0.01 Fig. 5a WS: f(x) = 0.41 + 0.0017·x 0.94 < 0.01 Fig. 5b MS: f(x) = 0.49‐0.0006·x 0.77 < 0.05 MS: f(x) = 1.01 + 0.0073·x 0.97 < 0.01 AS: f(x) = 1.50‐0.0003·x 0.82 < 0.05 AS: f(x) = 1.44 + 0.0049·x 0.99 < 0.01 Fig. 5c WS:

Responses of N&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;O and CH&amp;lt;sub&amp;gt;4&amp;lt;/sub&amp;gt; fluxes to fertilizer nitrogen addition rates in an irrigated wheat-maize cropping system in northern China

Abstract. Model and field studies generally posit that when the application rates of nitrogen fertilizer exceed crop needs, nitrous oxide (N2O) emissions will increase nonlinearly, though linear responses are also extensively reported by field studies. We conducted year-round measurements of crop yield, N2O and methane (CH4) fluxes for treatments of six fertilizer nitrogen levels (0, 135, 270, 430, 650 and 850 kg N ha−1 yr−1 in the form of urea) in a typical irrigated wheat-maize rotation field in northern China. Linear models characterized the responses of cumulative N2O emissions to fertilizer rates well; therefore, the calculated N2O emission factors of 0.17 ± 0.02%, 0.73 ± 0.05% and 0.49 ± 0.02% for the wheat season, maize season and annual scale, respectively, were appropriate for the different fertilizer rates. The cumulative CH4 uptake by the soil tended to be enhanced at higher fertilizer rates (≥350 kg N ha−1) in the maize season whereas no effect was observed for the wheat season. When the annual fertilizer rates increased from 270 to 430, from 270 to 650, and from 270 to 850 kg N ha−1 yr−1, the crop yields increased only 3 ∼ 15% (0.5 ∼ 2.1 t ha−1 yr−1), but cumulative N2O emissions increased 35 ∼ 115% (0.9 ∼ 3.0 kg N ha−1 yr−1). We recommend 270 kg N ha−1 yr−1 as the locally optimum fertilizer rate. Considering the nitrogen inputs by fertilization (270 kg N ha−1 yr−1), irrigation (4.3 ± 0.2 kg N ha−1 yr−1) and deposition (wet deposition: 30.5 ± 1.5 kg N ha−1 yr−1), the slightly positive soil nitrogen balance could maintain the current crop yield (∼13.8 t ha−1 yr−1) and reduce the present high N2O emissions (&gt;3.51 kg N ha−1 yr−1) of the local farmers' practice (fertilizer rate &gt; 430 kg N ha−1 yr−1).

Increased yield potential of wheat-maize cropping system in the North China Plain by climate change adaptation

In the North China Plain, the grain yield of irrigated wheat-maize cropping system has been steadily increasing in the past decades under a significant warming climate. This paper combined regional and field data with modeling to analyze the changes in the climate in the last 40 years, and to investigate the influence of changes in crop varieties and management options to crop yield. In particular, we examined the impact of a planned adaptation strategy to climate change -“Double-Delay” technology, i.e., delay both the sowing time of wheat and the harvesting time of maize, on both wheat and maize yield. The results show that improved crop varieties and management options not only compensated some negative impact of reduced crop growth period on crop yield due to the increase in temperature, they have contributed significantly to crop yield increase. The increase in temperature before over-wintering stage enabled late sowing of winter wheat and late harvesting of maize, leading to overall 4–6% increase in total grain yield of the wheat-maize system. Increased use of farming machines and minimum tillage technology also shortened the time for field preparation from harvest time of summer maize to sowing time of winter wheat, which facilitated the later harvest of summer maize.

Soil water storage, drainage, and leaching in four irrigated cotton-based cropping systems sown in a Vertosol with subsoil sodicity

Comparative studies of drainage and leaching in irrigated cotton (Gossypium hirsutum L.) based cropping systems in Australian Vertosols are sparse. Our objective was to quantify soil water storage, drainage, and leaching in four cotton-based cropping systems sown on permanent beds in an irrigated Vertosol with subsoil sodicity. Drainage was inferred using the chloride mass-balance method, and soil water storage and leaching were measured with a neutron moisture meter and ceramic-cup water samplers, respectively, from September 2005 to May 2011 in an ongoing experiment. The experimental treatments were: CC, cotton monoculture, summer cotton with winter fallow; CV, cotton–vetch (Vicia benghalensis L.) rotation with vetch stubble retained as in-situ mulch; CW, cotton–wheat (Triticum aestivum L.), with wheat stubble incorporated and a summer–winter fallow; and CWV, cotton–wheat–vetch, with wheat and vetch stubbles retained as in-situ mulch and summer and spring fallows. Soil water storage was generally highest under CW and CWV and least under CV. An untilled short fallow (~3 months) when combined with retention of crop residues as surface mulch, as in CWV, was as effective in harvesting rainfall as a tilled long fallow (~11 months) with stubble incorporation, as in CW. Drainage under cotton was generally in the order CW ≥ CWV &gt; CC = CV, all of which were considerably greater than drainage during fallows. Except for very wet and dry winters, drainage under wheat rotation crops was greater than that under vetch. During wet winters, saturated soil in the 0–0.6 m depth of treatments under fallow resulted in more drainage than in the drier, cropped plots. No definitive conclusions could be made with respect to the effects of cropping systems on salt and nutrient leaching. Leachate contained less nitrate-nitrogen, magnesium, and potassium, but leachate electrical conductivity was ~6 times higher than infiltrated water. The greater salinity of the leachate may pose a risk to groundwater resources.

Soil properties, black root-rot incidence, yield, and greenhouse gas emissions in irrigated cotton cropping systems sown in a Vertosol with subsoil sodicity

Comparative studies of soil quality and energy use in two- and three-crop rotations in irrigated cotton (Gossypium hirsutum L.) based cropping systems under varying stubble management practices in Australian Vertosols are sparse. Our primary objective was to quantify selected soil quality indices (salinity, sodicity, exchangeable cations, nitrate-N, pH), crop yields, and greenhouse gas emissions in four irrigated cotton-based cropping systems sown on permanent beds in a Vertosol with subsoil sodicity near Narrabri in north-western New South Wales. A secondary objective was to evaluate the efficacy of sowing vetch in rotation with cotton over a long period on the incidence of black root-rot in cotton seedlings. Results presented in this report pertain to the period June 2005–May 2011. The experimental treatments were: cotton–cotton; cotton–vetch (Vicia benghalensis L.); cotton–wheat (Triticum aestivum L.), where wheat stubble was incorporated; and cotton–wheat–vetch, where wheat stubble was retained as in-situ mulch. Vetch was terminated during or just before flowering by a combination of mowing and contact herbicides, and the residues were retained as in-situ mulch. Soil pH, electrical conductivity (EC1 : 5), Cl–, NO3–-N, exchangeable cations, exchangeable sodium percentage (ESP), electrochemical stability index (= EC1 : 5/ESP), and EC1 : 5/ESC (exchangeable sodium concentration) were evaluated in samples taken from the 0–1.2 m depth before sowing cotton during late September or early October of each year. Incidence of black root-rot was assessed 6 weeks after sowing cotton. Compared with sowing cotton every year, including wheat in cotton-based cropping systems improved cotton yield and reduced soil quality decline, emissions of carbon dioxide equivalents (CO2-e) per unit area, and CO2-e emissions per unit of cotton yield. Including vetch in the rotation was of negligible benefit in terms of yield and CO2-e emissions per unit of yield. The rate of soil quality decline was unaffected by including vetch in a cotton–wheat rotation but was accelerated when included in a cotton–cotton sequence. Among all cropping systems, soil quality was best with cotton–wheat and cotton–wheat–vetch but poorest with cotton–vetch. Although CO2-e emissions associated with growing 1 ha of cotton could be reduced by 9% by growing vetch because of substituting fixed atmospheric N for N fertiliser derived from fossil fuels, this advantage was partly negated by the emissions from farming operations associated with growing a vetch crop. Relative to a two-crop rotation (one cotton–one rotation crop), negligible benefits in terms of yield, soil quality, greenhouse gas emissions, and black root-rot control accrued from a three-crop rotation (one cotton–two rotation crops). Incidence of black root-rot increased as the number of cotton crops sown increased. In addition to the cropping systems, soil quality indices and yield were significantly influenced by irrigation water quality and climate.

Intensifying Groundnut Production in the Sudan Savanna Zone of Nigeria: Including Groundnut in the Irrigated Cropping Systems

Inadequate and erratic rainfall pattern and extreme temperature variations induced by climate change being experienced in Sudan savanna areas have compromised the cropping systems of these areas. A change in the cropping patterns is required to maintain and improve upon crop output levels. The pod yield ha(-1) and other growth and yield components of three varieties of groundnut grown under irrigated conditions were measured in a field experiment conducted at the Irrigation Research Station of the Institute for Agricultural Research, Zaria, from 2003 to 2006 dry seasons. Treatments consisted of three plant populations (50,000, 100,000 and 200,000 plants ha(-1)), three varieties (Samnut 23, Samnut 21 and Samnut 11) and three basin sizes (3 x 3, 3 x 4 and 3 x 5 m) arranged in a split plot design with population and variety as main plot and basin size as sub plot. Treatments were randomly assigned and replicated three times. Plant populations significantly affected plant height and canopy spread but had no effect on number of branches plant. Plants grew significantly taller at 200,000 plants ha(-1) while plant canopy spread was significantly widest at 50,000 plants ha(-1). Samnut 23 grew significantly taller than Samnut 21 and 11 although they exhibited wider canopies. Pod yield ha(-1) and 100 seed weight were significantly highest at 200,000 plants ha(-1). Samnut 23 produced the significantly highest pod yield ha(-1) and number of pods plant(-1). Samnut 11 produced significantly highest 100 seed weight. Samnut 23 planted at 200,000 plants ha(-1) in 3 x 4 m basins is most promising for irrigated groundnut cultivation in the Sudan savanna of Nigeria.

Cooking quality of upland and lowland rice characterized by different methods

Rice cooking quality is usually evaluated by texture and stickiness characteristics using many different methods. Gelatinization temperature, amylose content, viscosity (Brookfield viscometer and Rapid Visco Analyzer), and sensory analysis were performed to characterize culinary quality of rice grains produced under two cropping systems and submitted to different technologies. All samples from the upland cropping system and two from the irrigated cropping system presented intermediate amylose content. Regarding stickiness, BRS Primavera, BRS Sertaneja, and BRS Tropical showed loose cooked grains. Irrigated cultivars presented less viscosity and were softer than upland cultivars. Upland grain samples had similar profile on the viscoamylografic curve, but the highest viscosity peaks were observed for BRS Alvorada, IRGA 417, and SCS BRS Piracema among the irrigated cropping system samples. In general, distinct grain characteristics were observed between upland and irrigated samples by cluster analysis. The majority of the upland cultivars showed soft and loose grains with adequate cooking quality confirmed by sensory tests. Most of the irrigated cultivars, however, presented soft and sticky grains. Different methodologies allowed to improve the construction of the culinary profile of the varieties studied.

Nutrient and carbon balances in organic vegetable production on an irrigated, sandy soil in northern Oman

AbstractOur understanding of nutrient and carbon (C) fluxes in irrigated organic cropping systems of subtropical regions is limited. Therefore, leaching of mineral nitrogen (N) and phosphorus (P), gaseous emissions of NH3, N2O, CO2, and CH4, and total matter balances were measured over 24 months comprising a total cropping period of 260 d in an organic‐cropping‐systems experiment near Sohar (Oman). The experiment on an irrigated sandy soil with four replications comprised two manure types (ORG1 and ORG2) characterized by respective C : N ratios of 19 and 25 and neutral detergent fiber (NDF)‐to‐soluble carbohydrates (SC) ratios of 17 and 108. A mineral‐fertilizer (MIN) treatment with equivalent levels of mineral N, P, and potassium (K) served as a control. The three treatments were factorially combined with a cropping sequence comprising radish (Raphanus sativus L.) followed by cauliflower (Brassica oleracea L. var. botrytis) or carrot (Daucus carota subsp. sativus). Over the 24‐months experimental period gaseous N emissions averaged 45 kg ha–1 (59% NH3‐N, 41%N2O‐N) for MIN, 55 kg N ha–1 (69% NH3‐N, 31%N2O‐N) for ORG1, and 49 kg N ha–1 (59% NH3‐N, 41% N2O‐N) for ORG2. Carbon losses were 6.2 t ha–1 (98% CO2‐C, 2% CH4‐C) for MIN, 9.7 t C ha–1 (99% CO2‐C, 1% CH4‐C) for ORG1, and 10.6 t ha–1 (98% CO2‐C, 2% CH4‐C) for ORG2. Exchange resin–based cumulative leaching of mineral N amounted to 30 kg ha–1 for MIN, 10 kg ha–1 for ORG1, and 56 kg ha–1 for ORG2. Apparent surpluses of 361 kg N ha–1 and 196 kg P ha–1 for radish‐carrot and 299 kg N ha–1 and 184 kg P ha–1 for radish‐cauliflower were accompanied by K deficits of –59 kg ha–1 and –73 kg ha–1, respectively, for both cropping systems. Net C balances for MIN, ORG1, and ORG2 plots were –7.3, –3.1, and 1.5 t C ha–1 for radish‐carrot and –5.0, 1.3, and 4.6 t C ha–1 for radish‐cauliflower. The results underline the difficulty to maintain soil C levels in intensively cultivated, irrigated subtropical soils.

Wireless lysimeters for real-time online soil water monitoring

Identification of drainage water allows assessing the effectiveness of water management. Passive capillary wick-type lysimeters (PCAPs) were used to monitor water flux leached below the root zone under an irrigated cropping system. Wireless lysimeters were developed for web-based real-time online monitoring of drainage water using a distributed wireless sensor network (WSN). Twelve PCAP sensing stations were installed across the field at 90 cm below the soil surface, and each station measured the amount of drainage water using two tipping buckets mounted in the lysimeter and continually monitored soil water contents using two soil moisture sensors installed above the lysimeter. A weather station was included in the WSN to measure micrometeorological field conditions. All in-field sensory data were periodically sampled and wirelessly transmitted to a base station that was bridged to a web server for broadcasting the data on the internet. Communication signals from the in-field sensing stations to the base station were successfully interfaced using low-cost Bluetooth wireless radio communication. Field experiments resulted in high correlation between estimated and actual drainage with r2 = 0.95 and confirmed a reliable wireless communication throughout the growing season. A web-linked WSN system provided convenient remote online access to monitor drainage water flux and field conditions without the need for costly time-consuming supportive operations.

Field-specific potassium and phosphorus balances and fertilizer requirements for irrigated rice-based cropping systems

Fertilizer K and P requirements for rice (Oryza sativa L.) can be determined with site-specific nutrient management (SSNM) using estimated target yield, nutrient balances, and yield gains from added nutrient. We used the QUEFTS (QUantitative Evaluation of the Fertility of Tropical Soils) model with >8000 plot-level observations to estimate the relationship between grain yield and nutrient accumulation in above-ground dry matter of irrigated rice with harvest index ≥ 0.4. Predicted reciprocal internal efficiencies (RIEs) at 60–70% of yield potential corresponded to plant accumulation of 14.6 kg N, 2.7 kg P, and 15.9 kg K per tonne of grain yield. These RIEs enable determination of plant requirements for K and P and net output of K and P in harvested grain and removed crop residues at a target yield. Yield gains for nutrient applied to irrigated rice averaged 12% for K and 9% for P for 525 to 531 observations. For fields without certain yield gain, fertilizer K and P requirements can be determined by a partial maintenance approach (i.e., fertilizer input < output in nutrient balance), which considers nutrient supply mediated through soil processes and balances trade-offs between financial loss with full maintenance rates and risk of excessive nutrient depletion without nutrient application. When yield gains to an added nutrient are certain, partial maintenance plus yield gain can be used to determine fertilizer requirements. The SSNM-based approach and algorithms enable rapid development of field-specific K and P management.

NUTRIENT USE PATTERN IN THE IRRIGATED RICE-WHEAT CROPPING SYSTEM IN THE INDO-GANGETIC PLAINS OF HARYANA, INDIA

SUMMARYOn-farm nutrient management practices were evaluated in the irrigated rice-wheat cropping system (RWCS) in northwestern India. Large farmers used comparatively higher doses of nutrients than small and medium farmers for both rice and wheat crops. On average, a field is treated with organic manure after every 15 years for rice and 53 years for wheat. Nitrogen use was generally more than the recommended dose for both crops. Phosphorus use in wheat was nearly as per recommendation, while in rice it was below the recommended dose. Potassium use was almost nil; however, the use of Zn (particularly in rice) is becoming common. Use of biofertilizers was negligible. Overall, farmers applied higher doses of organic manures, K, Zn and biofertilizers in rice than wheat, and there was increasing trend in their use with increase in the size of land holdings. Grain yield increased significantly with increase in the size of land holding in rice but remained almost same in wheat. This study generated comprehensive data on nutrient use pattern in the RWCS, thus providing necessary input to researchers, planners and developmental agencies who wish to enhance food security.

Tillage and Inorganic Nitrogen Source Effects on Nitrous Oxide Emissions from Irrigated Cropping Systems

Nitrogen fertilization is essential for optimizing crop yields; however, it increases N2O emissions. The study objective was to compare N2O emissions resulting from application of commercially available enhanced‐efficiency N fertilizers with emissions from conventional dry granular urea in irrigated cropping systems. Nitrous oxide emissions were monitored from corn (Zea mays L.) based rotations receiving fertilizer rates of 246 kg N ha−1 when in corn, 56 kg N ha−1 when in dry bean (Phaseolus vulgaris L.), and 157 kg N ha−1 when in barley (Hordeum vulgare L. ssp. vulgare). Cropping systems included conventional‐till continuous corn (CT‐CC), no‐till continuous corn (NT‐CC), no‐till corn–dry bean (NT‐CDb), and no‐till corn–barley (NT‐CB). In the NT‐CC and CT‐CC systems, a controlled‐release, polymer‐coated urea (ESN) and dry granular urea were compared. In the NT‐CDb and NT‐CB rotations, a stabilized urea source (SuperU) was compared with urea. Nitrous oxide fluxes were measured during two growing seasons using static, vented chambers and a gas chromatograph analyzer. Cumulative growing season N2O emissions from urea and ESN application were not different under CT‐CC, but ESN reduced N2O emissions 49% compared with urea under NT‐CC. Compared with urea, SuperU reduced N2O emissions by 27% in dry bean and 54% in corn in the NT‐CDb rotation and by 19% in barley and 51% in corn in the NT‐CB rotation. This work shows that the use of no‐till and enhanced‐efficiency N fertilizers can potentially reduce N2O emissions from irrigated systems.

Greenhouse Gas Mitigation Economics for Irrigated Cropping Systems in Northeastern Colorado

Recent soil and crop management technologies have potential for mitigating greenhouse gas emissions; however, these management strategies must be profitable if they are to be adopted by producers. The economic feasibility of reducing net greenhouse gas emissions in irrigated cropping systems was evaluated for 5 yr on a Fort Collins clay loam soil (a fine‐loamy, mixed, superactive, mesic Aridic Haplustalf). Cropping systems included conventional tillage continuous corn (Zea mays L.) (CT‐CC), no‐till continuous corn (NT‐CC), and no‐till corn–bean (NT‐CB) including 1 yr soybean [Glycine max (L.) Merr.] and 1 yr dry bean (Phaseolus vulgaris L.). The study included six N fertilization rates ranging from 0 to 246 kg ha−1 Results showed highest average net returns for NT‐CB, exceeding net returns for NT‐CC and CT‐CC by US$182 and US$228 ha−1, respectively, at economically optimum N fertilizer rates. Net global warming potential (GWP) generally increased with increasing N fertilizer rate with the exception of NT‐CC, where net GWP initially declined and then increased at higher N rates. Combining economic and net GWP measurements showed that producers have an economic incentive to switch from CT‐CC to NT‐CB, increasing annual average net returns by US$228 ha−1 while reducing annual net GWP by 929 kg CO2 equivalents ha−1 The greatest GWP reductions (1463 kg CO2 equivalents ha−1) could be achieved by switching from CT‐CC to NT‐CC while also increasing net returns, but the presence of a more profitable NT‐CB alternative means NT‐CC is unlikely to be chosen without additional economic incentives.

Soilborne Pathogens of Cereals in an Irrigated Cropping System: Effects of Tillage, Residue Management, and Crop Rotation.

An irrigated cropping systems experiment was conducted for 6 years in east-central Washington State to examine agronomic and economic alternatives to continuous annual winter wheat (Triticum aestivum) with burning and plowing, and to determine how root diseases of cereals are influenced by management practices. The continuous winter wheat treatment with burning and plowing was compared with a 3-year no-till rotation of winter wheat-spring barley (Hordeum vulgare)-winter canola (Brassica napus) and three straw management treatments: burning, straw removal, and leaving the straw stubble standing after harvest. Take-all disease and inoculum increased from years 1 to 4 in the continuous winter wheat treatment with burning and plowing, reducing plant growth compared to the no-till treatments with crop rotations. Inoculum of Rhizoctonia solani AG-8 was significantly lower in the tilled treatment compared to the no-till treatments. Inoculum concentration of Fusarium pseudograminearum was higher than that of F. culmorum, and in one of three years, the former was higher in treatments with standing stubble and mechanical straw removal compared to burned treatments. Residue management method had no effect on Rhizoctonia inoculum, but spring barley had more crown roots and tillers and greater height with stubble burning. This 6-year study showed that irrigated winter wheat can be produced in a no-till rotation without major disease losses and demonstrated how cropping practices influence the dynamics of soilborne cereal diseases and inoculum over time.

Nitrogen, Tillage, and Crop Rotation Effects on Carbon Dioxide and Methane Fluxes from Irrigated Cropping Systems

Long-term effects of tillage intensity, N fertilization, and crop rotation on carbon dioxide (CO(2)) and methane (CH(4)) flux from semiarid irrigated soils are poorly understood. We evaluated effects of: (i) tillage intensity [no-till (NT) and conventional moldboard plow tillage (CT)] in a continuous corn rotation; (ii) N fertilization levels [0-246 kg N ha(-1) for corn (Zea mays L.); 0 and 56 kg N ha(-1) for dry bean (Phaseolus vulgaris L.); 0 and 112 kg N ha(-1) for barley (Hordeum distichon L.)]; and (iii) crop rotation under NT soil management [corn-barley (NT-CB); continuous corn (NT-CC); corn-dry bean (NT-CDb)] on CO(2) and CH(4) flux from a clay loam soil. Carbon dioxide and CH(4) fluxes were monitored one to three times per week using vented nonsteady state closed chambers. No-till reduced (14%) growing season (154 d) cumulative CO(2) emissions relative to CT (NT: 2.08 Mg CO(2)-C ha(-1); CT: 2.41 Mg CO(2)-C ha(-1)), while N fertilization had no effect. Significantly lower (18%) growing season CO(2) fluxes were found in NT-CDb than NT-CC and NT-CB (11.4, 13.2 and 13.9 kg CO(2)-C ha(-1)d(-1) respectively). Growing season CH(4) emissions were higher in NT (20.2 g CH(4) ha(-1)) than in CT (1.2 g CH(4) ha(-1)). Nitrogen fertilization and cropping rotation did not affect CH(4) flux. Implementation of NT for 7 yr with no N fertilization was not adequate for restoring the CH(4) oxidation capacity of this clay loam soil relative to CT plowed and fertilized soil.

Acerca de algumas das iniciativas empresariais e de I&D da cultura do algodoeiro em Portugal continental

Some business and research activities on upland cotton crop were carried out in Portugal in the middle of the XX century as well and in the first years of the XXI century, in order to introduce this crop in the south irrigated crop systems. However, environmental growing constrains, like low temperature at sowing and low temperature and raining during maturation and harvest, as well as national and European political options, determine crop abandon. In the present notes we collect and resume some information available about both those time periods.

Effects of tillage systems on soil organic carbon dynamics, structural stability and crop yields in irrigated wheat (Triticum aestivum L.)–cotton (Gossypium hirsutum L.) rotation in semi-arid Zimbabwe

In southern Africa, tillage research has focused on rainfed smallholder cropping systems, while literature on high-input irrigated cropping systems is limited. We evaluated the effects of conventional (CT), minimum (MT) and no-till (NT) tillage systems on soil organic carbon (SOC), bulk density, water-stable aggregates (WSA), mean weighted diameter (MWD) and crop yields in an irrigated wheat-cotton rotation. Soil data were mon- itored in the first and final year, while yields were monitored seasonally. Average bulk densities (1.5-1.7 Mg m -3 ) were similar among tillage systems, but often exceeded the critical limit (1.60 Mg m -3 )

Analysing farming practices to develop a numerical, operational model of farmers’ decision-making processes: An irrigated hay cropping system in France

Conventional water management in the Crau plain needs to be modified to ensure higher irrigation efficiency, better crop production and quality, and reduced environmental impacts. Because experimental approaches to test modifications of water management are difficult in relation to border irrigation, simulation may provide an alternative. We describe the development of a conceptual model of the decision-making process that determines the irrigation management of a cropping system, on which a simulation model is to be based. Interviews focused on water management were carried out, to understand how farmers manage their irrigation and how their decisions determine the technical system applied on the farm. These interviews were then analyzed using the “model for action” concept, to generate a conceptual model of the decision system, which is organized as a sequence of decision rules describing irrigation management. This model contains five elements: (1) spatial and temporal factors relevant to decision-making in terms of irrigation and hay cropping; (2) no interaction between the grassland cropping system and the sheep rearing system; (3) five rules to describe irrigation management in the cropping system; (4) major water distribution constraints; and (5) two inter-related operations, hay mowing and irrigation. The rules for irrigation decision-making are written as: “If <Indicator><Operator><Threshold> Then <Action1> Else <Action2>”. This conceptual model was used as the basis of a decision support system that includes models of grass growth and hydrology.

Nitrogen, Tillage, and Crop Rotation Effects on Nitrous Oxide Emissions from Irrigated Cropping Systems

We evaluated the effects of irrigated crop management practices on nitrous oxide (N(2)O) emissions from soil. Emissions were monitored from several irrigated cropping systems receiving N fertilizer rates ranging from 0 to 246 kg N ha(-1) during the 2005 and 2006 growing seasons. Cropping systems included conventional-till (CT) continuous corn (Zea mays L.), no-till (NT) continuous corn, NT corn-dry bean (Phaseolus vulgaris L.) (NT-CDb), and NT corn-barley (Hordeum distichon L.) (NT-CB). In 2005, half the N was subsurface band applied as urea-ammonium nitrate (UAN) at planting to all corn plots, with the rest of the N applied surface broadcast as a polymer-coated urea (PCU) in mid-June. The entire N rate was applied as UAN at barley and dry bean planting in the NT-CB and NT-CDb plots in 2005. All plots were in corn in 2006, with PCU being applied at half the N rate at corn emergence and a second N application as dry urea in mid-June followed by irrigation, both banded on the soil surface in the corn row. Nitrous oxide fluxes were measured during the growing season using static, vented chambers (1-3 times wk(-1)) and a gas chromatograph analyzer. Linear increases in N(2)O emissions were observed with increasing N-fertilizer rate, but emission amounts varied with growing season. Growing season N(2)O emissions were greater from the NT-CDb system during the corn phase of the rotation than from the other cropping systems. Crop rotation and N rate had more effect than tillage system on N(2)O emissions. Nitrous oxide emissions from N application ranged from 0.30 to 0.75% of N applied. Spikes in N(2)O emissions after N fertilizer application were greater with UAN and urea than with PCU fertilizer. The PCU showed potential for reducing N(2)O emissions from irrigated cropping systems.