Topdressing Fertilization Research Articles

On-farm experimentation of precision agriculture for differential seed and fertilizer management in semi-arid rainfed zones

Abstract Introduction This study explores the integration of precision agriculture technologies (PATs) in rainfed cereal production within semi-arid regions. Methods utilizing the Veris 3100 sensor for apparent soil electrical conductivity (ECa) mapping, differentiated management zones (MZs) were established in experimental plots in Valsalada, NE Spain. Site-specific variable dose technology was applied for seed and fertilizer applications, tailoring inputs to distinct fertility levels within each MZ. Emphasizing nitrogen (N) management, the study evaluated the impact of variable-rate applications on crop growth, yield, nitrogen use efficiency (NUE), and economic returns. For the 2021/2022 and 2022/2023 seasons, seeding rates ranged from 350 to 450 grains/m2, and basal fertilizer dosages varied between high and low levels. Additionally, the total nitrogen units were distributed differently between the two seasons, while maintaining a uniform topdressing fertilizer dose across all treatments. Results Results revealed a significant increase in yield in MZ 2 (higher fertility) compared to MZ 1 (lower fertility). NUE demonstrated notable improvement in MZ 2, emphasizing the effectiveness of variable-rate N applications. Economic returns, calculated as partial net income, showed a considerable advantage in MZ 2 over MZ 1, resulting in negative outcomes for low-fertility areas in several of the analyzed scenarios, and highlighting the financial benefits of tailored input management. Conclusion This research provides quantitative evidence supporting the viability and advantages of adopting PATs in rainfed cereal production. The study contributes valuable insights into optimizing input strategies, enhancing N management, and improving economic returns in semi-arid regions.

Cover Crops Affect Soil Mineral Nitrogen and N Fertilizer Use Efficiency of Maize No-Tillage System in the Brazilian Cerrado

Cover crops in no-tillage systems may alter soil mineral N and influence the N fertilizer use efficiency (NFUE) of subsequent maize. The hypothesis of this work is that no-tillage systems with cover crops affect nitrate, ammonium and maize NFUE in the Brazilian Cerrado. The objective was to evaluate the cover crop mineralization effect on soil N mineral and maize NFUE in a no-tillage system, with and without N topdressing. The experiment was arranged in a randomized block split-plot design. The plots were represented by cover crops (Cajanus cajan, Crotalaria juncea, Raphanus sativus and Mucuna aterrima). The subplots consisted of the application (WN) or non-application (NN) of N topdressing to maize. The soil was sampled in six layers (up to 60 cm) at the end (April) and at the beginning of the rainy season (November). NH4+ was lower for all cover crops and WN and NN management in April. NO3− differed between seasons and cover crops in WN and NN. The lignin concentration and N uptake of M. aterrima were the highest compared to other species. The highest NFUE was on R. sativus, showing higher fertilizer dependency. In a no-tillage system with cover crops, the N topdressing fertilization needs to be improved, considering mineralization.

Evaluation of top-dressing fertilization with nitrogen for the morphophysiology of wheat crops

Evaluation of top-dressing fertilization with nitrogen for the morphophysiology of wheat crops

Blended controlled-release nitrogen fertilizer increases rice post-anthesis nitrogen accumulation, translocation and nitrogen-use efficiency.

One-time application of blended controlled-release nitrogen fertilizer (CRN) has the potential to solve the difficulty of top-dressing fertilizer in the cultivation of rice and reduce the cost of CRN fertilizer application. However, its effects on rice dry matter and nitrogen (N) accumulation and translocation, yield and N-use efficiency (NUE) remain uncertain. Field experiments were carried out at three sites (Mingguang, Chaohu, and Guichi) in the Yangtze River Delta in China to compare the effects of the conventional split applications of urea and the blended CRN and on post-anthesis dry matter and N accumulation and translocation, yield, and NUE in rice at 0, 60, 120, 180, and 240kg N ha-1. The results showed that at the equal N application rates, compared under the conventional N fertilizer treatment, the blended CRN application significantly increased the rice yield by an average of 0.9-6.9%, mainly due to increase the number of spikelets per panicle. The highest yield achieved with blended CRN treatment occurred at 200kg N ha-1, with an NUE of 45.9%. Moreover, in comparison to the conventional N fertilizer, the blended CRN treatment increased pre-anthesis N translocation (Pre-NT) by 1.0-19.8%, and the contribution of pre-NT to grain N by 0.2-8.7%, and NUE by 3.2-28.4%. Meanwhile, the blended CRN treatment reduced labor costs by 1800 Yuan ha-1 and enhanced the economic gains by 21.5-68.8%. Therefore, one-time application of blended CRN ≤ 200kg N ha-1 application rate improved rice yield, NUE, and economic profit compared to equivalent rates of split applied conventional N fertilizers.

Greenhouse gas emissions of sewage sludge land application in urban green space: A field experiment in a Bermuda grassland

Sewage sludge land application is recognized as a strategy for recycling resource and replenishing soil nutrients. However, the subsequent greenhouse gas emissions following this practice are not yet fully understood, and the lack of quantitative research and field experiments monitoring these emissions hampers the establishment of reliable emission factors. This study investigated the greenhouse gas emission characteristics of sewage sludge land application through a field experiment that monitoring soil greenhouse gas fluxes. Seven nitrogen input treatments were implemented in a typical Bermuda grassland in China, with D and C representing the amendment of digested and composted sludge, respectively, at the nitrogen input rate of 0, 100, 200, and 300 kg N ha−1. Soil CH4, CO2, and N2O fluxes were measured throughout the entire experimental period, and soil samples from different treatments at various growth stages were analyzed. The results revealed that sewage sludge land application significantly increased soil N2O and CO2 emissions while slightly reducing soil CH4 uptake. The increased CO2 emissions were biogenic and carbon-neutral, mainly due to enhanced plant root respiration. The N2O emissions were the primary greenhouse gas emissions of sewage sludge land application, which were mainly concentrated in two 50-day periods following base and topdressing fertilization, respectively. N2O emissions following base fertilization by rotary tillage were substantially lower than those following topdressing fertilization. A logarithmic response relationship between N input rates and increased soil N2O emissions was observed, suggesting lower N2O emissions from sewage sludge land application compared to conventional N fertilizers at the same N input level. Future field experiments and meta-analysis are necessary to develop reliable greenhouse gas emission factors for sewage sludge land application.

Can machine learning models provide accurate fertilizer recommendations?

Accurate modeling of site-specific crop yield response is key to providing farmers with accurate site-specific economically optimal input rates (EOIRs) recommendations. Many studies have demonstrated that machine learning models can accurately predict yield. These models have also been used to analyze the effect of fertilizer application rates on yield and derive EOIRs. But models with accurate yield prediction can still provide highly inaccurate input application recommendations. This study quantified the uncertainty generated when using machine learning methods to model the effect of fertilizer application on site-specific crop yield response. The study uses real on-farm precision experimental data to evaluate the influence of the choice of machine learning algorithms and covariate selection on yield and EOIR prediction. The crop is winter wheat, and the inputs considered are a slow-release basal fertilizer NPK 25–6–4 and a top-dressed fertilizer NPK 17–0–17. Random forest, XGBoost, support vector regression, and artificial neural network algorithms were trained with 255 sets of covariates derived from combining eight different soil properties. Results indicate that both the predicted EOIRs and associated gained profits are highly sensitive to the choice of machine learning algorithm and covariate selection. The coefficients of variation of EOIRs derived from all possible combinations of covariate selection ranged from 13.3 to 31.5% for basal fertilization and from 14.2 to 30.5% for top-dressing. These findings indicate that while machine learning can be useful for predicting site-specific crop yield levels, it must be used with caution in making fertilizer application rate recommendations.

Unraveling the relationship between soil carbon-degrading enzyme activity and carbon fraction under biogas slurry topdressing

Biogas slurry, a by-product of the anaerobic digestion of biomass waste, predominantly consisting of livestock and poultry manure, is widely acclaimed as a sustainable organic fertilizer owing to its abundant reserves of essential nutrients. Its distinctive liquid composition, when tactfully integrated with a drip irrigation system, unveils immense potential, offering unparalleled convenience in application. In this study, we investigated the impact of biogas slurry topdressing as a replacement for chemical fertilizer (BSTR) on soil total organic carbon (TOC) fractions and carbon (C)-degrading enzyme activities across different soil depths (surface, sub-surface, and deep) during the tasseling (VT) and full maturity stage (R6) of maize. BSTR increased the TOC content within each soil layer during both VT and R6 periods, inducing alterations in the content and proportion of individual C component, particularly in the topsoil. Notably, the pure biogas slurry topdressing treatment (100%BS) compared with the pure chemical fertilizer topdressing treatment (CF), exhibited a 38.9% increase in the labile organic carbon of the topsoil during VT, and a 30.3% increase in the recalcitrant organic carbon during R6, facilitating microbial nutrient utilization and post-harvest C storage during the vigorous growth period of maize. Furthermore, BSTR treatment stimulated the activity of oxidative and hydrolytic C-degrading enzymes, with the 100%BS treatment showcasing the most significant enhancements, with its average geometric enzyme activity surpassing that of CF treatment by 27.9% and 27.4%, respectively. This enhancement facilitated ongoing and efficient degradation and transformation of C. Additionally, we screened for C components and C-degrading enzymes that are relatively sensitive to BSTR. The study highlight the advantages of employing pure biogas slurry topdressing, which enhances C component and C-degrading enzyme activity, thereby reducing the risk of soil degradation. This research lays a solid theoretical foundation for the rational recycling of biogas slurry.

Does the Deep Placement of Fertilizers Increase Potato Yields, Fertilization Efficiency and Reduce N2O Emissions from the Soil?

Despite the notable decline in potato cultivation areas across Poland and Europe, potatoes remain a crucial crop with diverse applications. Achieving the ambitious emission targets set by the EU for agricultural production may be easier with the practice of deep placement of slow-release fertilizers, which may increase yields and reduce greenhouse gas emissions. To examine the effect of deep placement of slow-release fertilizers on potato tuber yields, plant nutrient uptake, nutrient use efficiency, and soil N2O-N emissions, a two-year field experiment was conducted on loamy sand soil classified as Alblic Podzol (Ochric) soil, under temperate climate conditions prevailing in central Poland. The experiment involved a three-field rotation (potatoes, wheat, and peas), with potatoes being cultivated after peas in both years of the study. The experiment compared the effects of applying slow-release fertilizer at soil depths of 10 and 20 cm (DP10 and DP20) to fertilization with single-nutrient fertilizers applied to the soil surface (TD). The experiment utilized increasing doses of nitrogen and phosphorus, denoted as D0 (control), D1, D2, and D3, along with a standard dose of potassium across all tested fertilizer application methods. The results of this study confirmed that deep placement of slow-release fertilizers had limited effects on potato tuber yields. Deep placement of slow-release fertilizer increased plant nitrogen uptake by 2.8–13.5% compared to topdressing. Consequently, there was an improvement in nitrogen use efficiency from 29.8–75.0% on sites with fertilizer topdressing to 38.7–89.8% on sites with slow-release fertilizer deep placement. Phosphorus uptake by plants on sites with slow-release fertilizer deep placement was approximately 9.3–13.0% higher than on sites with fertilizer topdressing. This led to an enhancement in phosphorus use efficiency from about 15.1–19.5% on fertilizer topdressing sites to 19.4–25.4% on slow-release fertilizer deep placement sites. The impact of fertilizer deep placement was found to be less pronounced compared to the effects observed with increased nitrogen and phosphorus doses. The most important factors affecting tuber yield and nutrient use in potatoes were rainfall levels during the growing season. Deep fertilization did contribute to reduce soil N2O emissions by about 14%. However, further research involving different fertilization methods is needed to comprehensively assess the effectiveness of this practice in reducing greenhouse gas emissions.

Effects of nitrogen topdressing fertilization on yield and quality in soybeans

<p>Soybean [<italic>Glycine max</italic> (L.)] has higher nitrogen requirements than other crops. We investigated the effects on soybean yield and quality of topdressing with nitrogen fertilizer. Nitrogen fertilizer was applied as a topdressing to soybeans at 0, 20, 30, and 40 kg ha<sup>−1</sup> (N0, N20, N30, and N40 treatments, respectively); half of the total topdressing treatment was applied at the pre-flowering (R 1) stage and the other half at the post-flowering (R 2) stage. Yield was highest in the N20 treatment and decreased with larger quantities of topdressing. The protein and total amino acid content were highest in the N20 treatment but tended to decrease with a greater quantity of topdressing. contents of most individual amino acids peaked in the N20 or N30 treatments and decreased as topdressing quantity increased, although proline and arginine contents increased with quantity of topdressing. Isoflavone content tended to be highest in either the N30 or N20 treatment. The agronomic efficiency of nitrogen (AE<sub>N</sub>) was highest in the N20 treatment. There was a positive correlation between AE<sub>N</sub> and yield, protein, isoflavone, and amino acid content. Topdressing with 20 kg ha<sup>−1</sup> N produced the highest yield, protein, and amino acid content. Topdressing with greater quantities of nitrogen fertilizer decreased the yield and quality of soybeans.</p>

Soybean yield, seed protein and oil concentration, and soil fertility affected by off-season crops

The main cropping system in Brazil is soybean-maize off-season, particularly in tropical climate regions. However, there is a lack of information about the effects of alternative off-season crops on soybean performance and soil chemical fertility. The objective of this study was to evaluate, in a long-term experiment, the effects of off-season crops on soybean yield, seed protein and oil concentration, and soil chemical fertility under a no-tillage system. A seven-year experiment was conducted in Londrina, Paraná, Brazil. Treatments comprised six crop systems in the soybean off-season: (i) maize with nitrogen (N) fertilizer topdressing (80 kg N ha−1, (ii) maize without N fertilizer topdressing, (iii) wheat without N fertilizer topdressing, (iv) ruzigrass (Urochloa ruziziensis) without fertilizers, (v) showy rattlebox (Crotalaria spectabilis) without fertilizers, and (vi) unplanted fallow. Maize and wheat were used as cash crops and ruzigrass and showy rattlebox as cover crops. Ruzigrass had the highest straw production (average of 6.8 Mg ha−1 year−1) and improved soil fertility, especially organic carbon and potassium concentrations in the superficial soil layer. Ruzigrass and wheat off-season provided the highest soybean yields in succession (4311 and 4228 kg ha−1, respectively), whereas maize without N and fallow resulted in the lowest soybean yields (3841 and 3825 kg ha−1, respectively). Ruzigrass off-season provided the greatest yield stability of soybean and the fallow the lowest yield stability (coefficients of variation of 14.70 % and 23.78 %, respectively). The highest soybean seed protein concentration was observed with ruzigrass (368 g kg−1) and the lowest with fallow (353 g kg−1). The highest seed oil concentration was observed in maize with N and showy rattlebox (224 g kg−1 for both off-season crops) and the lowest with wheat (216 g kg−1). The ruzigrass provided the highest soybean seed protein and oil yields (1586 and 945 kg ha−1) and fallow the lowest (1352 and 845 kg ha−1). The ruzigrass used as soybean off-season cover crop improved the soil chemical fertility and soybean grain yield.

Disentangling the impact of biogas slurry topdressing as a replacement for chemical fertilizers on soil bacterial and fungal community composition, functional characteristics, and co-occurrence networks

The application of biogas slurry topdressing with drip irrigation systems can compensate for the limitation of traditional solid organic fertilizer, which can only be applied at the bottom. Based on this, we attempted to define the response of soil bacterial and fungal communities of maize during the tasseling and full maturity stages, by using a no-topdressing control and different ratios of biogas slurry nitrogen in place of chemical fertilizer topdressing. The application of biogas slurry resulted in the emergence of new bacterial phyla led by Synergistota. Compared with pure urea chemical topdressing, the pure biogas slurry topdressing treatment significantly enriched Firmicutes and Basidiomycota communities during the tasseling stage, in addition to affecting the separation of bacterial and fungal α-diversity indices between the tasseling and full maturity stages. Based on the prediction of community composition and function, the changes in bacterial and fungal communities caused by biogas slurry treatment stimulated the ability of microorganisms to decompose refractory organic components, which was conducive to turnover in the soil carbon cycle, and improved multi-element (such as sulfur) cycles; however it may also bring potential risks of heavy metal and pathogenic microbial contamination. Notably, the biogas slurry treatment reduced the correlation and aggregation of bacterial and fungal symbiotic networks, and had a dual effect on ecological randomness. These findings contribute to a deeper comprehension of the alterations occurring in soil microbial communities when substituting chemical fertilizers treated with biogas slurry topdressing, and promote the efficient and sustainable utilization of biogas slurry resources.

Multi-stage fertilizer recommendation for spring maize at the field scale based on narrowband vegetation indices

Crop fertilizer recommendations that are site-specific and can be adjusted in multiple growth stages can result in improved nutrient management, fertilizer use efficiency, and grain yield. There are considerable challenges to collecting a large number of soil and crop samples using the traditional methods, so a modern approach to developing fertilizer recommendations is urgently needed. In this study, we used the topdressing recommendation method based on unmanned aerial vehicle-based hyperspectral images and conducted a long-term nitrogen–phosphorus–potassium (NPK) combined fertilizer experiment in a spring maize cropping system. The hyperspectral imagery was acquired at multiple critical stages (jointing, silking, and maturity) in the experimental field containing 120 microplots during 2019–2020. The leaf nitrogen content (LNC) and yield measurement data for each microplot were also collected in multiple stages. Ten narrowband vegetation indices (VIs) were derived from the hyperspectral imagery as effective indicators for the estimation of the crop N status and grain yield. To develop topdressing recommendations for multiple stages, first, the optimal NPK fertilizer amounts, which were applied as the total fertilizer requirement to achieve the highest yield, were obtained. Second, the thresholds of the narrowband VIs, which justify if topdressing N fertilizer is needed, were calculated using the regression model established based on the relative yield and VIs. Finally, the N fertilizer amounts already applied in the jointing and silking stages were obtained based on the response of the narrowband VIs to the N fertilizer amounts. The results reveal that the optimal amount of N fertilizer is 180 kg ha−1, and the grain yield can be improved by using a combination of P and K fertilizers. Five VIs were significantly correlated with both the LNC and yield in the jointing and silking stages, and the thresholds of these VIs, below which topdressing fertilizer is needed, were identified at 95% of relative yield. The five VIs all presented high fitting accuracies with the amount of N fertilizer applied. However, there were noticeable differences in the sensitivities of the VIs in the jointing and silking stages. Therefore, we developed a cost-effective approach and provide multi-stage fertilizer recommendations at the field scale for the spring maize cropping system. This method can also benefit other precision agriculture applications if incorporated with remote sensing techniques.

Ammonia volatilization measured with the IHF method in a rainfed arable crop: Evaluation of tillage intensity and the number of experimental replicates

Ammonia (NH3) volatilization losses have severe impacts on human health, climate change and natural environments, but the effect of tillage intensity on these emissions has been barely evaluated in field conditions, particularly using micrometeorological methods, which require large surfaces. In this context, a field experiment in a barley (Hordeum vulgare L.) crop was set up in central Spain, in which NH3 volatilization losses from non-tilled plots (NT) were compared with those from conventionally tilled (T) plots, using the integrated horizontal flux (IHF) technique with three replicates. Ancillary soil and meteorological measurements were taken to explain NH3 fluxes, and the effect of the number of replicates on the results was statistically addressed. The highest NH3 emissions were obtained in NT plots after both basal (40 kg N ha−1 applied as urea) and top-dressing (120 kg N ha−1 applied as urea) fertilization events, while NH3 emission factors were higher after basal fertilization, in comparison with top-dressing application. Considering the sum of both periods, NT significantly increased NH3 emissions by 63 % with respect to T. We observed a notable influence of the number of replicates, since only two of the nine combinations of two replicates led to rejecting the null hypotheses. No tillage requires the optimized management of N (timing, rate and particularly source) to abate the potential side effects regarding NH3 volatilization, while the use of robust measurement methods (e.g. IHF) should be implemented with enough replicates to increase the precision in estimating differences.

The Effect of Mycorrhiza Fungi and Various Mineral Fertilizer Levels on the Growth, Yield, and Nutritional Value of Sweet Pepper (Capsicum annuum L.)

Mycorrhizal fungi can increase the effectiveness of a mineral fertilizer top dressing, positively affecting sweet pepper yield and quality. For this reason, an experiment was carried out between 2014 and 2016 to study the effect of top dressing doses and the inoculation of the root system with mycorrhizal fungi on the growth and yield of sweet pepper and the content of nutrients and macro- and microelements in the fruits. Root inoculation with Arbuscular Mycorrhizal Fungi (AMF) and mineral fertilizer doses were used as experimental factors with the following combinations: (1) mycorrhization: control (without AMF); AMF applied to the plant root zone during seedling production; AMF applied to the plant root zone after seedlings were transferred to pots; (2) top dressing doses: basic dose (100%); 50% of the basic dose; 25% of the basic dose. The sweet pepper fruits were harvested during physiological maturity. AMF inoculation of the root zone resulted in high sweet pepper yields of good quality. In particular, mycorrhizal fungi applied to the root system during seedling production positively affected the pepper yield and biometric characteristics, with fruits of the thickest pericarp and the largest mass. In the experimental units with AMF, the reduction in the top dressing fertilizer dose by 50% and 75% did not cause a statistically significant decrease in the yield of peppers and did not result in a deterioration of the biometric characteristics of the plants and fruits or a reduction in the biological value of the fruits. Despite the reduction in top dressing dose by 50% and 75%, AMF contributed to the accumulation of similar amounts of phosphorus in the sweet pepper fruits. The top dressing dose of 50% applied during seedling production to the experimental units with mycorrhizal fungi resulted in a significant increase in the content of potassium, calcium, and magnesium. A significant increase in the amount of sodium in the fruits was noted in the experimental units with mycorrhizal fungi applied to the roots when the seedlings were transferred to pots. To summarize, the application of mycorrhizal fungi to the pepper root zone during seedling production is recommended because it has a positive effect on the yield and its quality. In the unit with mycorrhiza, a lower dose of mineral fertilizers did not result in a significant decrease in the yield of pepper fruits.

The Extension of Vegetable Production to High Altitudes Increases the Environmental Cost and Decreases Economic Benefits in Subtropical Regions

Global warming has driven the expansion of cultivated land to high-altitude areas. Intensive vegetable production, which is generally considered to be a high economic value and high environmental risk system, has expanded greatly in high-altitude mountainous areas of China. However, the environmental cost of vegetable production in these areas is poorly understood. In this study, pepper production at low (traditional pepper production area) and high (newly expanded area) altitudes were investigated in Shizhu, a typical pepper crop area. The output and environmental cost at the two altitudes were identified. the influence of resource inputs, climate, and soil properties on pepper production was evaluated. There were obvious differences in output and environmental cost between the two altitudes. High-altitude pepper production achieved a 16.2% lower yield, and had a higher fertilizer input, resulting in a 22.3% lower net ecosystem economic benefit (NEEB), 23.0% higher nitrogen (N) footprint and 24.0% higher carbon (C) footprint compared to low-altitude farming. There is potential for environmental mitigation with both high- and low-altitude pepper production; Compared to average farmers, high-yield farmers groups reduced their N and C footprints by 16.9–24.8% and 18.3–25.2%, respectively, with 30.6–34.1% higher yield. A large increase in yield could also be achieved by increasing the top-dress fertilizer rate and decreasing the plant density. Importantly, high-altitude pepper production was achieved despite less advanced technology and inferior conditions (e.g., a poor road system and uneven fields). It provides a reference for the study of the environmental cost of other high-altitude regions or other crop systems at high-altitude areas.

Developing a nitrogen fertilizer management model for wheat in calcareous soils using the critical nitrogen dilution curve

The critical nitrogen (N) dilution curve, which expresses whole-plant critical N concentration as a function of shoot biomass, can be used as a N management diagnostic tool for cereals. The objectives of this research were to develop a critical N dilution curve for wheat grown in calcareous soils and to formulate a model for estimating N fertilizer requirement of wheat crop at different growth stages. Six N fertilization rates (0–250 kg N ha−1) were used to induce variability in plant growth throughout six site-years (three locations at West Delta of Egypt and two seasons [2020/21-2021/22]). Aboveground shoot biomass (W; Mg DM [dry matter] ha−1) and N concentration (Nc; g kg−1 DM) were determined on five sampling dates during the growing season. A critical N dilution curve was developed as: {N}_{mathrm{c}}=50.141 {mathrm{W}}^{-0.424}. The Nc dilution curve was then used to develop a N fertilizer topdressing strategy. The study relied on N nutrition index inferred from the Nc based on N uptake, and instead of relying on a single N recovery efficiency coefficient, a variable N recovery efficiency was developed. This approach increased the hypothetical N requirements at low N application rates while decreased requirements at high N application rates, implying that the Nc dilution curve can be used successfully to estimate the rates of supplemental N application. The developed strategy will provide a solid basis for precisely managing N fertilizer, though challenge ahead at the farm level will be in determining the actual shoot biomass and N concentration.

The Yield-Forming Role of Nitrogen in Rice in the Growing Seasons with Variable Thermal Conditions

A reduced basal and increased topdressing fertilizer rate (RBIT) can usually increase rice yield, but whether this practice alleviates the impact of poor weather on rice production is unknown. Thus, the effect of three integrated RBIT treatments (RBITs, including RBIT alone, RBIT in combination with straw incorporation (RBITS) or a reduced fertilizer rate (RBITR)) on rice growth and nutritional status under different weathers was investigated in a 9-year experiment. Conventional fertilization (CF) was the control. We found that daytime temperature and light (DTL) after heading were the main meteorological factors limiting rice yield increases. RBITs did not affect rice yield under High-DTL, compared with CF, but RBITS significantly increased rice yield under Low-DTL. Compared with High-DTL, the positive effect of RBIT and RBITR on the N concentration and proportion in vegetative organs under Low-DTL was higher than the K concentration in vegetative organs, but RBITS showed the opposite trend. Regression analysis indicated that the harvest index had stronger correlations with the N concentration (negative), K concentration (positive), and N/K (negative) in vegetative organs under Low-DTL than under High-DTL. Our findings suggested that RBITS could improve rice adaptability to daytime temperature and light changes after heading by balancing crop nutritional status (N/K).

Developing a tactical nitrogen fertilizer management strategy for sustainable wheat production

Syncronizing plant available water with soil nitrogen (N) remains a critical aspect of agronomic management to enhance crop yield, grain quality, farmers’ profit, and environmental sustainability. Their interaction is essential expecially in landscapes characterized by a highly spatial and temporal range of pedoclimatic conditions. To support farmers in making more informed decisions, validate dynamic process based crop simulation models have been successfully used to optimize N fertlization. In this study, we aimed to develop a tactical N fertilizer management strategy to increase profitability, improve grain quality and reduce N losses. The SALUS model was tested against measured durum wheat grain yield and grain quality data collected across independent farmers’ fields in Tuscany (Italy). The model was then used to optimize N fertilization under different potential plant extractable soil water (PESW) conditions at the second topdressing N fertilization timing. The model was tested against measurements of grain yield and protein concentration at harvest, as well as phenological stage, biomass, and plant N content during the growing season. Simulations were carried out for 30 years of available weather, using different N rates. The simulations allowed the identification of optimal N rates for each PESW condition and soil type concerning economic and environmental sustainability. Results showed higher yield and higher leaching for the silty clay soil (Quercia; QUE) than for the loamy soil (Arbia; ARB). No major differences were predicted for protein content across soils. Profitability and emissions increased as N rate increased. The N fertilization strategy locally adopted by farmers was also analyzed across different PESW conditions at 2nd topdressing fertilization in comparison to other adopted N management strategies (timing of application and fertilization rates). The model showed that the conventional fertilization strategy does not maximize socio-ecological benefits, but was also the lowest among all the strategies tested. The maximum economic benefit for farmers was reached by applying 90 kg N at 1st and 60 kg N at 2nd topdressing fertilization, both in dry (due to sufficient soil water storage in the soil) and wet years. These results provide valuable insights for developing strategies that balance sustainability, resilience, quality, and profitability in wheat crop production in central Italy.

Analysis of factors affecting technical efficiency of A1 smallholder maize farmers under command agriculture scheme in Zimbabwe: The case of Chegutu and Zvimba Districts

In an effort to address the decline in maize productivity, the government of Zimbabwe in 2016/17 endorsed a special program for input support named command agriculture scheme (CAS). Against this background, the study questioned the beneficiaries’ technical efficiency and factors that influence farmers to gravitate towards the frontier using Chegutu and Zvimba districts of Zimbabwe as case studies. The study used a cross-sectional survey of 240 households randomly selected through a three-stage multiple-sampling procedure. The single-stage modelling stochastic frontier approach was applied to assess technical efficiency of A1 smallholder command agriculture maize farmers. The study revealed that A1 smallholder command agriculture maize farmers in Chegutu and Zvimba districts were technically efficient at 85% and 94%, respectively. The major determinants of technical efficiency were basal fertilizer, labour, area allocated to maize production and topdressing fertilizer which all indicated a positive relationship. The main determinants of technical inefficiency were age, maize farming experience, level of education, marital status, occupation status and other sources of income. Results further revealed that farmers from Chegutu district had increasing returns to scale (1.43) while farmers from Zvimba district had decreasing returns to scale (0.54). The study therefore argues that despite the observed high technical efficiencies, Chegutu farmers could bridge their 15% gap between the observed output and the frontier output by focusing more on input usage with increasing returns to scale while Zvimba farmers could bridge their 6% gap by focusing more on socio-economic drivers of technical inefficiency given their decreasing returns to scale.

Nutrient dynamics in water and soil under conventional rice cultivation in the Vietnamese Mekong Delta.

Background The evaluation of nutrient variability plays a crucial role in accessing soil potentials and practical intervention responses in rice production systems. Synthetic fertilizer applications and cultivation practices are considered key factors affecting nutrient dynamics and availability. Here, we assessed the nutrient dynamics in surface, subsurface water and soil under local water management and conventional rice cultivation practices in the Vietnamese Mekong Delta. Methods We implemented a field experiment (200 m 2) in the 2018 wet season and the 2019 dry season in a triple rice-cropping field. Eight samples of surface water, subsurface water (30-45 cm), and topsoil (0-20 cm) were collected and analysed during the rice-growing seasons. Results The results showed that N-NH 4 +, P-PO 4 3- and total P peaks were achieved after fertilizing. Irrespective of seasons, the nutrient content in surface water was always greater than that of subsurface water ( P < 0.001), with the exception of N-NO 3 -, which was insignificant ( P > 0.05). When comparing the wet and dry seasons, nutrient concentrations exhibited minor differences ( P > 0.05). Under conventional rice cultivation, the effects of synthetic fertilizer topdressing on the total N, soil organic matter (SOM), and total P were negligible in the soil. Higher rates of N fertilizer application did not significantly increase soil N-NH 4 +, total N, yet larger P fertilizer amounts substantially enhanced soil total P ( P < 0.001). Conclusions Under conventional rice cultivation, N-NH 4 +, P-PO 4 3- and total P losses mainly occur through runoff rather than leaching. While N-NO 3 - loss is similar in surface water and subsurface water. Notably, nutrient content in soil was high; whilst SOM was seen to be low-to-medium between seasons. Future work should consider the nutrient balance and dynamic simulation in the lowland soil of the Vietnamese Mekong Delta's paddy fields.