Conventional Application Rate Research Articles

Optimized nutrients management improved citrus yield and fruit quality in China: A meta-analysis

Clarifying current situation of farmers' fertilization and yield in citrus producing areas and the effects of different fertilization measures can provide a scientific basis for improving the yield and quality of citrus in China. We retrieved 92 literatures on citrus fertilization from the CNKI and Web of Science to examine the impacts of nitrogen (N), phosphorus (P or P2O5), and potassium (K or K2O) fertilizer dosage and partial productivity under farmers' conventional fertilization and experts' optimized fertilization, as well as the effects of optimized fertilization measures on citrus yield and quality by using meta-analysis approach. The average conventional application rates of N, P2O5, and K2O were 507.3, 262.2, and 369.3 kg·hm-2 in citrus production in China. Compared with conventional fertilization, optimized fertilization resulted in a reduction of N and P2O5 by 14.7% and 8.3%, an increase in K2O application by 6.6%, which promoted partial productivity of N, P2O5, and K2O fertilizers by 7.8%, 18.4%, and 14.7%, correspondingly. The optimized fertilization resulted in 11.9% and 2.8% increase in fruit yield and single fruit weight, while improved vitamin C content (Vc, 3.1%), total soluble solids (TSS, 5.9%) and total sugar content (TSC, 8.6%). Additionally, it also led to a reduction in titratable acid (TA, -3.4%) and total acid content (TAC, -3.6%), and consequently elevated the TSS/TA (14.0%) and TSC/TAC (9.5%). Among different optimized fertilization methods, the effect of optimized NPK + medium and/or micro element fertilizer on citrus yield and fruit quality was the best, especially NPK decrement ≤25% between optimized NPK measures. The effect of conventional NPK + organic fertilizer was higher than conventional NPK + medium and/or micro element fertilizer. However, different citrus varieties, including mandarins, pomelos, and oranges, showed different responses to optimized fertilization. Optimized fertilization management could synergistically improve citrus yield, fertilizer use efficiency, and fruit quality. Therefore, the strategy of integrated nutrient management1 with reducing NPK fertilizer, balancing medium and/or micro nutrient fertilizer and improving soil fertility by organic fertilizer should be adopted according to local conditions in citrus producing areas of China.

Straw and phosphorus applications promote maize (Zea mays L.) growth in saline soil through changing soil carbon and phosphorus fractions.

Straw return has been widely recognized as an important carbon (C) enhancement measure in agroecosystems, but the C-phosphorus (P) interactions and their effects on plants in saline soils are still unclear. In this study, we investigated the effects of straw return and three P application levels, no P fertilizer (Non-P), a conventional application rate of P fertilizer (CP), and a high application rate of P fertilizer (HP), on maize growth and soil C and P fractions through a pot experiment. The results revealed that the dry matter weight of maize plant was no difference between the two straw return levels and was 15.36% higher under HP treatments than under Non-P treatments. Plant nutrient accumulations were enhanced by straw addition and increased with increasing P application rate. Straw application reduced the activities of peroxidase (POD), superoxide dismutase (SOD), catalase, and the content of malondialdehyde (MDA) in maize plants by 31.69%, 38.99%, 45.96% and 27.04%, respectively. P application decreased SOD, POD activities and MDA content in the absence of straw. The contents of easily oxidized organic carbon (EOC), particulate organic carbon (POC) and the ratio of POC/SOC in straw-added soils were 10.23%, 17.00% and 7.27% higher, respectively, than those in straw-absent soils. Compared with Non-P treatments, HP treatments led to an increase of 12.05%, 23.04% in EOC, POC contents respectively, while a decrease of 18.12% in the contribution of MAOC to the SOC pool. Straw return improved the P status of the saline soil by increasing soil available P (14.80%), organic P (35.91%) and Ca2-P contents (4.68%). The structural equation model showed that straw and P applications could promote maize growth (indicated by dry matter weight, P accumulation, antioxidant enzyme activity and MDA content) through improving soil C and P availabilities. This study provides evidence that straw return together with adequate P supply in saline soil can promote crop nutrient accumulation, attenuate the oxidation damage on crop growth, and be beneficial for SOC turnover and soil P activation.

Biochar combined with different nitrogen fertilization rates increased crop yield and greenhouse gas emissions in a rapeseed-soybean rotation system

Biochar as agricultural soil amendment has been extensively investigated for its potential to sequester carbon, to mitigate greenhouse gases (GHGs) emissions, to enhance soil fertility and enhance crop yields. In this study, we investigated the impact of varying N fertilization rates in conjunction with biochar on soil properties, crop yield, and GHGs emissions in a rapeseed (Brassica napus L.)-soybean (Glycine max (L.) Merrill) rotation system for one year. Biochar and N fertilizer were applied following a factorial combination design of three biochar (B0: 0 t hm−2, B1: 15 t hm−2, and B2: 60 t hm−2) and three N fertilizer application rates (H: 100%, M: 75%, and L: 50% of the conventional application rates). In general, there was no significant effect of N fertilizer and its interaction with biochar application on soil water content, pH, and total carbon content, but the addition of biochar significantly increased these parameters (P < 0.05). The yield of both crops were significantly augmented by biochar up to 75% compared to using N fertilization alone, potentially due to enhanced N use efficiency. However, biochar significantly increased the cumulative N2O and CH4 emissions by as much as 2.2 times and 19 times, respectively, during the rapeseed season, thereby elevating the global warming potential (GWP) and the yield-scaled GWP. Nevertheless, the significantly increased soil carbon content following biochar addition might boost soil carbon sequestration, which could counterbalance the escalating GWP induced by GHGs. Therefore, we recommend a comprehensive and long-term evaluation of biochar's impact by considering crop yield, GHGs emissions, and carbon sequestration in agricultural systems to ensure sustainable agricultural management.

Determining application volume of unmanned aerial spraying systems for cotton defoliation using remote sensing images

The Unmanned aerial spraying systems (UASS), with a precise positioning system and convenient control system, have attracted more attention from researchers and the market. However, the UASS operation parameter setting still depends on the operator, and there is still a gap between the intelligent spraying. The upgrade of UASS from automation to intelligence requires a “scientific brain” to make spraying decisions. In this study, the UASS equipped with centrifugal nozzles was used to simulate defoliant spraying, combined with RGB and multi-spectral cameras to collect remote sensing images of the target area. The droplet distribution data were obtained through two years of field trials in two places. A droplet distribution prediction model based on the spray volume of UASS and the remote sensing spectral index that characterizes the cotton canopy structure is established by the BP neural network and Bayesian regularization training algorithm. The cotton defoliant was verified using this model and combined with NY/T 3213–2018 standard. The research results show that it is feasible to use remote sensing images to determine the application volume of UASSs for cotton defoliant. Compared with the conventional application rate and overspray, the defoliant spray based on the decision model can achieve the expected cotton defoliation effect and reduce the application volume.

Interactive effect of irrigation and blend ratio of controlled release potassium chloride and potassium chloride on greenhouse tomato production in the Yellow River Basin of China

Soil water and fertilizer are two main factors affecting tomato yield and quality, and their optimization management is crucial for sustainable production. There are many studies about the response of tomato growth and fruit yield formation to irrigation level and potassium (K) fertilizer, but few studies have been conducted on the responses of irrigation level and controlled release potassium chloride (CRK), not to mention the different irrigation levels and CRK to KCl blending ratios. In this study, two consecutive growing seasons (2020–2021) tomato pot experiments were presented with three irrigation levels (W100, W80, and W60) and three blending ratios of CRK to KCl (100%, 80%/20%, 60%/40%) under the condition that the amount of potassium fertilizer was reduced by 40% compared with conventional application rate. The results revealed that under W80 water conditions, 80% CRK mixed with 20% KCl application led to a significant increase in tomato yield by 4.1–11.9% and 4.6–18.9%, K use efficiency by 11.5–34.2% and 6.1–32.3%, fruit vitamin C content by 9.3–25.3% and 5.6–28.3%, fruit soluble sugar content by 10.2–20.0% and 10.2–24.1% in 2020 and 2021, respectively, compared with the other K fertilization treatments. Meanwhile, the water use efficiency and fruit soluble solid content of W80K80 treatment were also maintained at a high level. Molecular analysis shows that the W80K80 treatment had a higher photosynthetic rate, rubisco content, cytokinin content, and osmotic regulation substances content, and lower abscisic acid (ABA), malondialdehyde (MDA), and hydrogen peroxide (H2O2) contents. Our results indicated that 80% irrigation level and 80% CRK-20% KCl blending ratio were the optimal water and K supply mode for tomato production in this study. The result provided useful information regarding greenhouse tomato production that would allow the achievement of higher fruit yield, quality and resource use efficiencies, and provided theoretical and technical support for greenhouse tomato irrigation and K fertilizer application technologies.

Replacing nitrogen fertilizer with nitrogen-fixing cyanobacteria reduced nitrogen leaching in red soil paddy fields

Excessive chemical nitrogen (N) fertilizer application and flood irrigation in rice production can lead to substantial soil-N losses and low nitrogen-use-efficiency (NUE) in rice due to N leaching from red paddy soils. Although inoculation of irrigated fields with nitrogen-fixing cyanobacteria (NFC) has been shown to increase rice yield, there are few studies on N leaching and NUE in response to NFC when used in place of urea. A two-year field experiment was carried out to examine the concentrations of ammonium-N (NH4+-N), nitrate-N (NO3−-N), total dissolved N (TDN) and dissolved organic N (DON) in percolated irrigation water, as well as cumulative leaching losses after NFC was used to replace different application rates of urea in double cropped rice grown in red paddy soil. Four treatments were established: 1) CK, the control with no application of urea or NFC; 2) N10C0, a conventional full application of urea only; 3) N5C5, addition of a half-application of NFC to replace half of the conventional application rate of urea (N5C5); and 4) N0C10, a full application of NFC only. In 2017 and 2018, although the average rice yield of N0C10 was 25.0 % higher than that of CK, it was 23.8 % lower than that of N10C0. The average NUE of N10C0 was 34.7 %, and the average TDN leaching loss was 13.9 kg ha-1 per crop each year. Correspondingly, NUE of N5C5 was 47.7 %, which was 37.5 % higher than that of N10C0. Replacing 50 % of urea with NFC did not significantly decrease rice yield, but it reduced TDN leaching by 37.2 %. The results showed that the conventional way of fertilization caused the most N loss, while replacing partial urea with NFC significantly reduced the leaching losses of NH4+-N, NO3−-N and DON. Moreover, replacing 50 % of urea with NFC can retain more soil N than conventional fertilization at the end of the rice season because NFC can intercept, fix and delay release of N. Thus, the multiple functions of NFC in N cycling dynamics are more conducive to the retention of N by soil and greatly reduces N leaching.

Development of a Novel Model of Soil Legacy P Assessment for Calcareous and Acidic Soils

Phosphate (P) rock is a finite natural resource, and its use for P fertilizer production has resulted in its rapid depletion worldwide. In order to reduce the use of natural P resources, reducing the input of P into agricultural systems is necessary. The assessment of legacy P in soil is an option to maintain crop yield with low P fertilizer input. Many models have been tested to assess the contribution of legacy soil P to crop uptake. However, these models face a common challenge as conceptual soil P pools in models cannot be accurately initiated and evaluated using measured soil P indexes. In this study, a novel legacy P assessment (LePA) model was developed according to empirical equations about crop P uptake, soil Olsen-P, and total P from two long-term fertilizer experiments in typical calcareous and acidic soils in China. We used the DPPS (dynamic phosphorus pool simulator) model as a contrast model to estimate the simulation accuracy of the new LePA model. The calibration and validation datasets for both models were set-up by collecting data from two long-term fertilizer experiments in typical calcareous and acidic soils in China. The results showed that the LePA model simulated crop P uptake similar to the DPPS model in calcareous soil. While the DPPS model failed to depict crop P uptake under low pH conditions, the LePA model worked well after modification when limited crop growth caused by acidic conditions was considered. Moreover, the LePA model can also predict changes in soil TP and Olsen-P with P fertilizer application, which are new functions compared with the DPPS model. Based on a scenario analysis generated by the LePA model, P fertilizer application could be reduced by 52% in Yangling and 46% in Qiyang compared with the conventional application rate during this period to maintain the current yields if soil legacy P can be utilized efficiently. The LePA model is a useful tool for guiding soil P management from the field to country scales.

Variation of Soil Bacterial and Fungal Communities from Fluvo-Aquic Soil Under Chemical Fertilizer Reduction Combined with Organic Materials in North China Plain

Since 2015, China has implemented chemical fertilizer reduction, aiming to achieve zero growth in the application rate of chemical fertilizer. Therefore, it is of great significance to explore the effect of chemical fertilizer reduction combined with organic materials in a wheat-maize rotation system from fluvo-aquic soil in North China on soil microbial community. The field experiment included five fertilization treatments, i.e., chemical fertilizer with conventional application rate (F), chemical fertilizer reduction on the basis of conventional fertilization (FR), chemical fertilizer reduction plus straw (FRS), chemical fertilizer reduction combined with organic fertilizer (FRO), and chemical fertilizer reduction combined with organic fertilizer and straw (FROS). The abundance, composition, diversity, and structure of bacterial and fungal communities among treatments were evaluated using qPCR and Illumina high-throughput sequencing technology. The results showed that the concentrations of soil organic matter (SOM) and total nitrogen (TN) in all treatments with addition of organic materials were much higher than those in treatments applied with only chemical fertilizer. The SOM content in the FRS, FRO, and FROS treatments increased by 23.91%, 37.12%, 26.09%, and the TN content increased by 11.96%, 21.08%, 15.22% in comparison with the F treatment, respectively. The lowest contents of available phosphorus (AP) and nitrate nitrogen (NO3−-N) were observed in FR treatment. The AP content in FRO and FROS treatments were 2.44 times and 2.42 times greater than that in FR treatment, respectively. Compared with F treatment, the organic materials input significantly increased bacterial and fungal abundances. More significant effects on the α-diversity with organic fertilizer were observed in the fungal community compared with the bacterial community. The significant increase of Ascomycota and the decline of Mortierellomycota and Glomeromycota were observed in the combined with organic materials treated soils. The nonmetric multidimensional scaling (NMDS) analysis demonstrated that the bacterial community structure in the F treatment was clearly separated from the other treatments, and the other treatments clustered closely, while with respect to fungal community structure, the FRO and FROS treatments grouped together and were separated from the other three treatments. The redundancy analysis (RDA) results showed that the structure of the bacterial community was significantly correlated with SOM and TN, and the fungal community structure was strongly correlated with AP, SOM, and TN. The chemical fertilizer reduction combined with organic fertilizer and straw can effectively improve soil fertility and nutrient availability, altered the community structure of both bacteria and fungi, but only significantly reduced fungal biodiversity. The influence of chemical fertilizer reduction combined with organic materials on fungi was greater than that on bacteria in fluvo-aquic soil of North China.

Effects of application of inhibitors and biochar to fertilizer on gaseous nitrogen emissions from an intensively managed wheat field

The effects of biochar combined with the urease inhibitor, hydroquinone, and nitrification inhibitor, dicyandiamide, on gaseous nitrogen (N2O, NO and NH3) emissions and wheat yield were examined in a wheat crop cultivated in a rice-wheat rotation system in the Taihu Lake region of China. Eight treatments comprised N fertilizer at a conventional application rate of 150kgNha−1 (CN); N fertilizer at an optimal application rate of 125kgNha−1 (ON); ON+wheat-derived biochar at rates of 7.5 (ONB1) and 15tha−1 (ONB2); ON+nitrification and urease inhibitors (ONI); ONI+wheat-derived biochar at rates of 7.5 (ONIB1) and 15tha−1 (ONIB2); and, a control. The reduced N fertilizer application rate in the ON treatment decreased N2O, NO, and NH3 emissions by 45.7%, 17.1%, and 12.3%, respectively, compared with the CN treatment. Biochar application increased soil organic carbon, total N, and pH, and also increased NH3 and N2O emissions by 32.4–68.2% and 9.4–35.2%, respectively, compared with the ON treatment. In contrast, addition of urease and nitrification inhibitors decreased N2O, NO, and NH3 emissions by 11.3%, 37.9%, and 38.5%, respectively. The combined application of biochar and inhibitors more effectively reduced N2O and NO emissions by 49.1–49.7% and 51.7–55.2%, respectively, compared with ON and decreased NH3 emission by 33.4–35.2% compared with the ONB1 and ONB2 treatments. Compared with the ON treatment, biochar amendment, either alone or in combination with inhibitors, increased wheat yield and N use efficiency (NUE), while addition of inhibitors alone increased NUE but not wheat yield. We suggest that an optimal N fertilizer rate and combined application of inhibitors+biochar at a low application rate, instead of biochar application alone, could increase soil fertility and wheat yields, and mitigate gaseous N emissions.

Scenario analysis of fertilizer management practices for N2O mitigation from corn systems in Canada

Effective management of nitrogen (N) fertilizer application by farmers provides great potential for reducing emissions of the potent greenhouse gas nitrous oxide (N2O). However, such potential is rarely achieved because our understanding of what practices (or combination of practices) lead to N2O reductions without compromising crop yields remains far from complete. Using scenario analysis with the process-based model DNDC, this study explored the effects of nine fertilizer practices on N2O emissions and crop yields from two corn production systems in Canada. The scenarios differed in: timing of fertilizer application, fertilizer rate, number of applications, fertilizer type, method of application and use of nitrification/urease inhibitors. Statistical analysis showed that during the initial calibration and validation stages the simulated results had no significant total error or bias compared to measured values, yet grain yield estimations warrant further model improvement. Sidedress fertilizer applications reduced yield-scaled N2O emissions by c. 60% compared to fall fertilization. Nitrification inhibitors further reduced yield-scaled N2O emissions by c. 10%; urease inhibitors had no effect on either N2O emissions or crop productivity. The combined adoption of split fertilizer application with inhibitors at a rate 10% lower than the conventional application rate (i.e. 150kgNha−1) was successful, but the benefits were lower than those achieved with single fertilization at sidedress. Our study provides a comprehensive assessment of fertilizer management practices that enables policy development regarding N2O mitigation from agricultural soils in Canada.

Effects of Compost and Gypsum on Soil Water Movement and Retention of a Reclaimed Tidal Land

Compost and gypsum can be used to ameliorate soil physicochemical properties in reclaimed tidal lands as an organic and inorganic amendment, respectively. To evaluate effects of compost and gypsum on soil water movement and retention as a soil physical property, we measured the soil’s saturated hydraulic conductivity and field capacity after treating the soil collected in a reclaimed tidal land with compost and gypsum. Saturated hydraulic conductivity of soil increased when compost was applied at the conventional application rate of 30 Mg ha -1 . However, the further application of compost insignificantly (P > 0.05) increased saturated hydraulic conductivity. On the other hand, additional gypsum application significantly increased soil saturated hydraulic conductivity while it decreased soil field capacity, implying the possible effect of gypsum on flocculating soil colloidal particles. The results in this study suggested that compost and gypsum can be used to improve hydrological properties of reclaimed tidal lands through increasing soil water retention and movement, respectively.

Nitrogen dynamics of anaerobically digested slurry used to fertilize paddy fields

To determine nitrogen (N) fate and environmental impact of applying anaerobic digestion slurry (ADS) to rice paddy (Oryza sativa L.), a field experiment was established using three treatments based on contrasting N application rate. The ADS (with ammonium-N accounting for >80 % of total N) treatment at a conventional application rate of 270 kg N ha−1 was compared to a negative control (no N fertilizer) and a positive control of urea applied at 270 kg N ha−1. The N budget showed the following distribution of applied N from ADS and urea: 41.3 ± 5.1 % for ADS and 36.6 ± 4.4 % for urea recovered by the rice plant (including straw, grain, and root), 16.4 ± 3.7 % for ADS and 7.4 ± 1.8 % for urea lost via ammonia volatilization, 0.26 ± 0.15 % for ADS and 0.15 ± 0.12 % for urea lost by direct N2O emission, 1.9 ± 0.5 % for ADS and 2.3 ± 0.8 % for urea leached downward, 0.70 ± 0.15 % for ADS and 0.67 ± 0.12 % for urea discharged with floodwater drainage, and 39.4 ± 8.4 % for ADS and 53.0 ± 9.1 % for urea retained by soil or lost by N2 emission. Compared to urea application, ADS application impacts the environment mainly through gaseous N losses rather than water N losses. ADS application had a positive impact on rice grain yield and reduced chemical fertilizer use. Considering the wide distribution of paddy fields and the ever-increasing quantities of ADS, ADS may serve as a valuable N source for rice cultivation, although mitigating ammonia and N2O losses should be further investigated.

Recovery efficiency and loss of 15N-labelled urea in a rice–soil system in the upper reaches of the Yellow River basin

Chemical N input is essential for high rice yields. However, low recovery efficiency of chemical fertilizer N with flooding irrigation in the anthropogenic-alluvial soil resulted in N lost from the rice field in Ningxia Irrigation Region in the upper reaches of the Yellow River. With the technique of stable isotope 15N-traced urea, we conducted two years experiment to estimate the recovery efficiency and loss of applied chemical fertilizer in a rice field. The three fertilizer N treatments included 300kgha−1 (N300, the conventional application rate), 240kgha−1 (the optimized N application amount, N240) and no N fertilizer application treatment (CK). We estimated the recovery of 15N-labelled urea in grain, straw and root of rice and residues in soil profile. The 15N not accounted for in the plant and soil was presumably lost. The results showed that more efficient use of N fertilizer could allow current N application rates to reduce by 20%. This would still maintain crop yields while substantially reducing N losses to the environment. The high N fertilizer application increased the N uptake by rice derived from fertilizer, and the amount of N rice taken up from soil reduced correspondingly, which resulted in the higher N surplus in soil. Under the conventional irrigation and fertilizer management level, the recovery rate of 15N-labelled urea in rice–soil system was about 48–49%. The 15N-labelled fertilizer recovery in rice plant (Ndff) was 26–30%. In the paddy soil profiles of 0–90cm, the residual of 15N-labelled fertilizer in soil (Ndfs) were 54–70kgha−1, and N residual rate in soils were 18–23%. The annual N loss from the rice field in the Irrigation Region was 28,865tons. The distribution of 15N abundance variability in different soil profile indicated that fertilizer N leached into the deep soil layers along with irrigation water as a result of continuous yearly rice planting. Optimization of nitrogen fertilizer can significantly reduce the amount of N residuals and N loss from the paddy field. Compared with N300, optimized nitrogen fertilizer application could decrease the loss of fertilizer N by 22–34kgha−1, and reduce the amount of N surplus by 26–33kgha−1 while the dry matter of rice increased 8–15% and N uptake by rice increased 2–6%. Considering the high food production and the minimum environmental threat, we should fully take into account the optimization application by reducing fertilizer N inputs. However, the interaction between irrigation management and N application rate on N use efficiency in alkaline anthropogenic-alluvial soil needs to be further studied.

Nitrogen Balance and Loss in a Greenhouse Vegetable System in Southeastern China

High rates of fertilizer nitrogen (N) are applied in greenhouse vegetable fields in southeastern China to maximize production; however, the N budgets of such intensive vegetable production remain to be explored. The goal of this study was to determine the annual N balance and loss in a greenhouse vegetable system of annual rotation of tomato, cucumber, and celery at five N (urea) application rates (0, 348, 522, 696, and 870 kg N ha −1 year −1). Total N input to the 0–50 cm soil layer ranged from 531 to 1 053 kg ha −1, and N fertilizer was the main N source, accounting for 66%–83% of the total annual N input. In comparison, irrigation water, wet deposition, and seeds in total accounted for less than 1% of the total N input. The fertilizer N use efficiency was only 18% under the conventional application rate of 870 kg N ha −1 and decreased as the application rate increased from 522 to 870 kg N ha −1. Apparent N losses were 196–201 kg N ha −1, of which 71%–86% was lost by leaching at the application rates of 522–870 kg N ha −1. Thus, leaching was the primary N loss pathway at high N application rates and the amount of N leached was proportional to the N applied during the cucumber season. Moreover, dissolved organic N accounted for 10% of the leached N, whereas NH 3 volatilization only contributed 0.1%–0.6% of the apparent N losses under the five N application rates in this greenhouse vegetable system.

Fate of applied urea 15N in a soil-maize system as affected by urease inhibitor and nitrification inhibitor

A micro-plot field experiment with reduced urea &lt;sup&gt;15&lt;/sup&gt;N application was conducted to study the effects of urease inhibitor NBPT (N-(&lt;i&gt;n&lt;/i&gt;-butyl) thiophosphoric triamide) and nitrification inhibitor DMPP(3,4-dimethyl-1H-pyrazolium dihydrogen) on the fate of applied urea &lt;sup&gt;15&lt;/sup&gt;N; it aimed to find an efficient way to reduce the urea N application rate while improving the agronomic and environmental benefits. Five treatments were installed, i.e., 180 kg N/ha (N&lt;sub&gt;1&lt;/sub&gt;, conventional application rate), 126 kg N/ha (N&lt;sub&gt;2&lt;/sub&gt;, reduced to 70% conventional application rate), N&lt;sub&gt;2&lt;/sub&gt; + NBPT, N&lt;sub&gt;2&lt;/sub&gt; + DMPP, and N&lt;sub&gt;2&lt;/sub&gt; + NBPT + DMPP. Compared with treatment N&lt;sub&gt;1&lt;/sub&gt;, all the other treatments had a significantly higher total &lt;sup&gt;15&lt;/sup&gt;N recovery by both soil and plant (&lt;i&gt;P&lt;/i&gt; &lt; 0.05 48.20, 41.39, 37.69, 38.85 and 34.83% soil recovery for N&lt;sub&gt;2&lt;/sub&gt; + NBPT + DMPP, N&lt;sub&gt;2&lt;/sub&gt; + DMPP, N&lt;sub&gt;2&lt;/sub&gt; + NBPT, N&lt;sub&gt;2&lt;/sub&gt; and N&lt;sub&gt;1&lt;/sub&gt;treatment, respectively; and 42.68, 40.86, 40.25, 37.18 and 36.30% plant recovery for N&lt;sub&gt;2&lt;/sub&gt; + NBPT + DMPP, N&lt;sub&gt;2&lt;/sub&gt; + DMPP, N&lt;sub&gt;2&lt;/sub&gt; + NBPT, N&lt;sub&gt;2&lt;/sub&gt;, and N&lt;sub&gt;1&lt;/sub&gt; treatment, respectively). In the plant &lt;sup&gt;15&lt;/sup&gt;N recovery, the &lt;sup&gt;15&lt;/sup&gt;N absorbed in grain/stem was highest in treatment N&lt;sub&gt;2&lt;/sub&gt; + NBPT + DMPP. The maize biomass and the maize yield had a slight increase in treatment N&lt;sub&gt;2&lt;/sub&gt; + NBPT + DMPP, compared with those in treatment N&lt;sub&gt;1&lt;/sub&gt;. In sum, for the maize production in study area, N&lt;sub&gt;2&lt;/sub&gt; + NBPT + DMPP application method would be a feasible way to ensure the normal maize yield while improving yield quality, saving urea fertilizer, and protecting the environment.

AmaizeN: A decision support system for optimizing nitrogen management of maize

AmaizeN is a decision support system to help maize growers schedule nitrogen (N) fertilizer applications for site-specific maize crops. It forecasts crop yields and N-fertilizer application rates for potential yield and best economic returns, and predicts the consequences of user management decisions. It takes into account both crop production and environmental impact. In this article we describe the system functionality and underlying crop models, and the system validity and effectiveness evaluated in 16 field trials covering a wide range of weather and soil conditions. At each trial site crops received either two or four N-fertilizer application rates, including one rate recommended by AmaizeN. The AmaizeN-predicted maize yields matched field measurements well ( r 2 = 0.77; p < 0.001 for silage, and r 2 = 0.55; p < 0.001 for grain), and gave a reasonably good indication of silage crude protein content ( r 2 = 0.28; p < 0.001) and silage harvest date ( r 2 = 0.71; p < 0.0006). The system was also capable of estimating N-leaching during the cropping season and predicting residual soil mineral-N at the end of the season ( r 2 = 0.47; p < 0.001), but more effort is needed to improve the accuracy of some predictions. In all instances the AmaizeN-recommended N-fertilizer strategy was more efficient than the growers’ practice. Recommended N-fertilizer rates were on average 85 kg ha −1 less than conventional application rates across 10 crops, with no yield reduction. Its recommended higher-than-conventional application rate at another crop brought about a significant yield increase. System development was guided by an industry user group who requested the decision support system interface to be ‘simple and easy to use’. To ensure user adoption of the system some compromises in system prediction accuracy were required. Local agricultural production conditions were also incorporated.

Nitrogen fate and environmental consequence in paddy soil under rice-wheat rotation in the Taihu lake region, China

Field undisturbed tension-free monolith lysimeters and 15N-labeled urea were used to investigate the fate of fertilizer nitrogen in paddy soil in the Taihu Lake region under a summer rice-winter wheat rotation system. We determined nitrogen recovered by rice and wheat, N remained in soil, and the losses of reactive N (i.e., NH3, N2O, NO3−, organic N and NH4+) to the environment. Quantitative allocation of nitrogen fate varied for the rice and wheat growing seasons. At the conventional application rate of 550 kg N ha−1 y−1 (250 kg N ha−1 for wheat and 300 kg N ha−1 for rice), nitrogen recovery of wheat and rice were 49% and 41%, respectively. The retention of fertilizer N in soil at harvest accounted for 29% in the wheat season and for 22% in the rice season. N losses through NH3 volatilization from flooded rice paddy was 12%, far greater than that in the wheat season (less than 1%), while N leaching and runoff comprised only 0.3% in the rice season and 5% in the wheat season. Direct N2O emission was 0.12% for the rice season and 0.14% for the wheat season. The results also showed that some dissolved organic N (DON) were leached in both crop seasons. For the wheat season, DON contributed 40–72% to the N- leaching, in the rice season leached DON was 64–77% of the total N leaching. With increasing fertilizer application rate, NH3 volatilization in the rice season increased proportionally more than the fertilizer increase, N leaching in the wheat season was proportional to the increase of fertilizer rate, while N2O emission increased less in proportion than fertilizer increase both in the rice season and wheat season.

Fate of 15N-Labeled Urea Under a Winter Wheat-Summer Maize Rotation on the North China Plain

A field experiment was conducted to investigate the fate of 15N-labeled urea and its residual effect under the winter wheat ( Triticum aestivum L.) and summer maize ( Zea mays L.) rotation system on the North China Plain. Compared to a conventional application rate of 360 kg N ha −1 (N360), a reduced rate of 120 kg N ha −1 (N120) led to a significant increase ( P < 0.05) in wheat yield and no significant differences were found for maize. However, in the 0–100 cm soil profile at harvest, compared with N360, N120 led to significant decreases ( P < 0.05) of percent residual N and percent unaccounted-for N, which possibly reflected losses from the managed system. Of the residual fertilizer N in the soil profile 25.6%–44.7% and 20.7%–38.2% for N120 and N360, respectively, were in the organic N pool, whereas 0.3%–3.0% and 11.2%–24.4%, correspondingly, were in the nitrate pool, indicating a higher potential for leaching loss associated with application at the conventional rate. Recovery of residual N in the soil profile by succeeding crops was less than 7.5% of the applied N. For N120, total soil N balance was negative; however, there was still considerable mineral N (NH + 4-N and NO − 3-N) in the soil profile after harvest. Therefore, N120 could be considered agronomically acceptable in the short run, but for long-term sustainability, the N rate should be recommended based on a soil mineral N test and a plant tissue nitrate test to maintain the soil fertility.

Simulation and model comparison of unsaturated movement of pesticides from a large clay lysimeter

A long-term (>10 months) leaching experiment was conducted with a large clay soil column and a rain simulator to study unsaturated transport of the nematicide aldicarb and the herbicide simazine in a cracked clay soil. Water retention and soil conductivity were derived from experimental outflow data and deterministic parameter estimation techniques. Under conventional application rates and realistic rain events, aldicarb's aerobic metabolites were found in very high concentrations, and did not meet the normal EC levels for water during the entire measuring period. A mass balance for aldicarb showed that 0.35% of the initial dose was leached. However, when the two isosteric metabolites aldicarb-sulfoxide and aldicarb-sulfone were included in the mass balance, this percentage increased dramatically to 19.7%. Simazine was found in relatively low concentrations of 0.05–0.6 μg/l, and only 0.11% of the initial dose was leached over 280 days. The absence of a `breakthrough behaviour' (peak exposure) implies long term delivery (chronic exposure) of the compound from the soil. The predictive performances of the widely used pesticide leaching models VARLEACH, LEACHP, MACRO, PESTLA and SIMULAT, which differ in their basic concepts for calculating water and solute transport and pesticide behaviour, were compared. This ring test revealed that none of the models were able to describe both water percolation and pesticide leaching to a completely satisfying degree. Moreover, there is little agreement on maximum pesticide concentrations and the time period in which these occur. This conclusion seriously limits the possibilities of model application and conducting reliable risk assessments for pesticides which are applied on the studied, or similar type of clay soils.

Susceptibility of Selected Woody Plants to Pelleted Picloram

Susceptibility of Selected Woody Plants to Pelleted Picloram