Title Exploring the Impacts of Genotype-Management-Environment Interactions on Wheat Productivity, Water Use Efficiency, and Nitrogen Use Efficiency under Rainfed Conditions

Wheat production under rainfed conditions is restrained by water scarcity, elevated temperatures, and lower nutrient uptake due to possible drought. The complex genotype, management, and environment (G × M × E) interactions can obstruct the selection of suitable high yielding wheat cultivars and nitrogen (N) management practices prerequisite to ensure food security and environmental sustainability in arid regions. The agronomic traits, water use efficiency (WUE), and N use efficiencies were evaluated under favorable and unfavorable weather conditions to explore the impacts of G × M × E on wheat growth and productivity. The multi-N rate (0, 70, 140, 210, and 280 kg N ha−1) field experiment was conducted under two weather conditions (favorable and unfavorable) using three wheat cultivars (AUR-809, CHK-50, and FSD-2008) in the Pothowar region of Pakistan. The experiments were laid out in randomized complete block design (RCBD), with split plot arrangements having cultivars in the main plot and N levels in the subplot. The results revealed a significant decrease in aboveground biomass, grain yield, crop N-uptake, WUE, and N use efficiency (NUE) by 15%, 22%, 21%, 18%, and 8%, respectively in the unfavorable growing season (2014–2015) as compared to favorable growing season (2013–2014) as a consequence of less rainfall and heat stress during the vegetative and reproductive growth phases, respectively. FSD-2008 showed a significantly higher aboveground biomass, grain yield, crop N-uptake, WUE, and NUE as compared to other wheat cultivars in both years. Besides, N140 appeared as the most suitable dose for wheat cultivars during the favorable growing season. However, any further increase in N application rates beyond N140 showed a non-significant effect on yield and yield components. Conversely, the wheat yield increased significantly up to 74% from N0 to N70 during the unfavorable growing season, and there was no substantial difference between N70–N280. The findings provide opportunities for maximizing yield while avoiding excessive N loss by selecting suitable cultivars and N application rates for rainfed areas of Pothowar Plateau by using meteorological forecasting, amount of summer rainfall, and initial soil moisture content.

A Crop Simulation Model for Tef (Eragrostis tef (Zucc.) Trotter)

Tef is an Ethiopian staple grain that provides both food security and income for smallholders. As tef is nutritious and gluten free, it is also gaining popularity as a health food. A tef model was calibrated based on the Decision Support System for Agrotechnology Transfer’s (DSSAT) NWheat model and included parameter changes in phenology, photoperiod response, radiation use efficiency, and transpiration efficiency for both standard and elevated atmospheric CO2, based on published literature for tef and other C4 species. The new DSSAT-Tef model was compared with tef field experiments. DSSAT-Tef accurately simulated phenology and responded to changes in N supply and irrigation, but overestimated growth and occasionally yields. Simulation-observation comparisons resulted in an RMSE of 2.5 days for anthesis, 4.4 days for maturity, 2624 kg/ha (49.6%) for biomass, and 475 kg/ha (41.0%) for grain yield. Less data were available for N uptake, and the model simulated crop N uptake with an RMSE of 45 kg N/ha (46.2%) and 15 kg N/ha (37.3%) for grain N. While more data from contrasting environments are needed for further model testing, DSSAT-Tef can be used to assess the performance of crop management strategies, the suitability of tef for cultivation across growing environments, and food security.

Nitrogen use efficiency of 15N urea applied to wheat based on fertiliser timing and use of inhibitors

Improving fertiliser nitrogen (N) use efficiency is essential to increase productivity and avoid environmental damage. Using a 15N mass balance approach, we investigated the effects of five N fertiliser management strategies to test the hypothesis that increasing uptake of applied N by wheat improves productivity and reduces loss of N in a semi-arid environment. Three experiments were conducted between 2012 and 2014. Treatments included urea application (50 kg N/ha) at sowing with and without nitrification inhibitor (3,4-dimethylpyrazole phosphate, DMPP) and surface broadcast with and without urease inhibitor (n-butyl thiophosphoric triamide, NBPT) at the end of tillering plus an unfertilised control. It was found that deferring fertiliser application until the end of tillering decreased losses of fertiliser N (35–52%) through increasing uptake by the crop and or recovery in the soil at harvest, while maintaining yield except when rainfall following application was low. In this case, deferring application reduced fertiliser uptake (− 71%) and grain yield (− 18%) and increased recovery of N in the soil (+ 121%). Use of DMPP or NBPT reduced N loss where seasonal conditions were conducive to denitrification during winter (DMPP) and volatilisation or denitrification later in the season (NBPT). Their effect on grain yield was less significant; DMPP increased yield (+ 3–31%) in all years and NBPT increased yield (+ 7–11%) in 2 of 3 years compared to unamended urea. The majority of crop N uptake was supplied from soil reserves and as a result, crop recovery of applied N was not strongly related to grain yield response.

Can split or delayed application of N fertiliser to grain sorghum reduce soil N2O emissions from sub-tropical Vertosols and maintain grain yields?

Most soil nitrous oxide (N2O) emissions from rain-fed grain sorghum grown on sub-tropical Vertosols in north-west New South Wales, Australia, occur between fertiliser nitrogen (N) application at sowing and booting growth stage. At three experiments, we investigated the potential for deferring some (split-N) or all (delayed) fertiliser N until booting to mitigate N2O produced without compromising optimum crop yields. N products included urea, 3,4-dimethyl pyrazole phosphate (DMPP)-urea, polymer-coated urea (PCU) and N-(n-butyl)thiophosphoric triamide (NBPT)-urea. For a fourth experiment, the N fertiliser rate was varied according to pre-sowing soil mineral N stocks left by different previous crops. All experiments incorporated 15N mini-plots to determine whether delayed or split-N affected crop N uptake or residual soil N. Compared to urea applied at-sowing, delayed applications of urea, DMPP-urea or NBPT-urea at booting reduced the N2O emission factor (EF, percentage of applied N emitted) by 67–81%. Crop N uptake, grain yield and protein tended to be lower with delayed N than N at-sowing due to dry mid-season conditions. Much of the unused N remained in the soil at harvest. Split-N (33% sowing:67% booting) using urea, reduced EF by 59% compared to at-sowing urea, but maintained crop N uptake, grain yield and protein. Using DMPP-urea or PCU for the at-sowing portion of the split reduced EF by 84–86%. Grain yield was maintained using PCU, but was lower with DMPP-urea, which had more N in vegetative biomass. Using NBPT-urea for the in-crop portion of the split did not affect N2O emissions or crop productivity. Nitrogen budgeting to account for high pre-sowing soil mineral N nullified urea-induced N2O emissions. An N-budgeted, split-N strategy using urea offers the best balance between N2O mitigation, grain productivity and provision of a soil mineral N buffer against dry mid-season conditions. Split-N using DMPP-urea or PCU further enhanced N2O mitigation but there was no yield response to justify the extra expense.

RELIABILITY OF NDVI DERIVED BY HIGH RESOLUTION SATELLITE AND UAV COMPARED TO IN-FIELD METHODS FOR THE EVALUATION OF EARLY CROP N STATUS AND GRAIN YIELD IN WHEAT

SUMMARYThis study was aimed at comparing in-field parameters and remote sensing NDVI (normalized difference vegetation index) by both satellite (SAT) and unmanned aerial vehicle (UAV) for the assessment of early nitrogen (N) status and prediction of yield in winter wheat (Triticum aestivum L.). Six increasing N rates, i.e., 0, 40, 80, 120, 160, 200 kg N ha−1 were applied, half at tillering and half at shooting. Thus, when the crop N status was monitored between the two N applications, consecutive N treatments differentiated from each other by just 20 kg N ha−1. The following in-field and remote sensed parameters were compared as indicators of crop vegetative and N status: plant N% (w:w) concentration; crop N uptake (Nupt); ratio between transmitted and incident photosynthetically active radiation (PARt/PARi); leaf SPAD values, an indirect index for chlorophyll content; SAT and UAV derived NDVI. As reliable indicators of wheat N availability, in-field parameters were ranked as follows: PARt/PARi ≅ Nupt > SPAD ≅ N%. The PARt/PARi, Nupt and SPAD resulted quite strongly correlated to each other. At all crop stages, the NDVI was strongly correlated with PARt/PARi and Nupt. It is of relevance that NDVI correlated quite strongly to in-field parameters and grain yield at shooting, i.e., before the second N application, when the N rate can still be adjusted. The SAT and UAV NDVIs were strongly correlated to each other, which means they can be used alternatively depending on the context.

Development of methods for remotely sensing grass growth to enable precision application of nitrogen fertilizer

A ‘chessboard’ field experiment set up to investigate how the yield response to nitrogen (N) fertiliser varied spatially within a field in the UK indicated that the optimum N rate varied substantially by up to 100 kg N/ha within the three hectare experimental area. Variation in N optima was negatively related to the soil N supply. However, soil N supply, yield potential and apparent fertiliser recovery rate were inter-related which meant that the influence of each element on N optima was complex. Spectral reflectance indices related well to crop N uptake and could be used to help estimate soil N supply.