High Fertilizer Application Research Articles

Erect panicle architecture contributes to increased rice production through the improvement of canopy structure

The erect panicle architecture has contributed to the improvement of yield in japonica rice breeding, and recent molecular analysis has revealed the mechanisms involved in individual plant yield increases. However, the population structure is more important in rice production compared with individual plant yield. Our study compared the population canopy structure of a curved panicle variety Sasanishiki (WT) and an erect panicle mutant derived from CRISPR/Cas9 gene editing at the DENSE AND ERECT PANICLE 1 (DEP1) locus. The results showed that more light could reach to the leaves under the panicle in the CRISPR-dep1 population compared with the WT. The canopy of the CRISPR-dep1 population exhibited higher temperature and lower humidity compared with the WT after heading. A subsequent survey showed that the CO2 concentration in the CRISPR-dep1 population was significantly lower than that in the WT population from full heading to 15 days after heading. Moreover, the increase of biomass in the CRISPR-dep1 population was greater than that in the WT. We noticed that the CRISPR-dep1 mutant could achieve higher yield under low fertilization application compared with the WT under high fertilizer application through increased transplant density. These traits could contribute to an agricultural sustainable development strategy. The quality investigation showed that the dep1 allele increased the yield along with imposing a penalty on grain quality. Our study not only elucidated the mechanism of yield improvement in an erect panicle architecture variety from the perspective of population structure optimization but also provides a theoretical basis for supporting cultivation systems with the erect panicle architecture.

Weather forecasts to enhance an Irish grass growth model

Abstract Grass growth models have retrospectively predicted grass growth in Ireland using weather observations. However, to predict future grass growth to aid farm management, weather forecasts are necessary inputs. The Moorepark St. Gilles grass growth model (MoSt GGM) is mechanistic and was developed to predict perennial ryegrass growth on any Irish farm. To date, it has used local farm information, (retrospective) weather data and management factors to predict daily paddock-level grass growth. Here, we include weather forecasts in the MoSt GGM and assess its performance through two studies: daily grass growth predictions at four nitrogen fertiliser application levels using weather forecasts up to ten days in advance were compared with those using weather observations; and the GGM predictions for an Irish dairy farm using observed and forecast weather were compared with on-farm grass growth observations from 2013 to 2016. In the first study, all weather inputs captured the rise in grass growth predictions with higher fertiliser application. Based on the Root Mean Squared Error (RMSE), European Centre for Medium-Range Weather Forecasts (ECMWF) forecasts outperformed a forecast based on climatological averages as GGM inputs up to six days in advance, and up to ten days in advance after bias correction. In the second study, ECMWF forecasts were the best weather forecast to predict grass growth since they captured weather variability well and did not require the local weather observations necessary for bias corrections. Weather forecasts are useful inputs to the MoSt GGM, and yield accurate weekly predictions that could aid management decisions.

Physiological and Developmental Response of Selected Upland Rice Genotypes to Water and Nutrient Stress Condition

Drought is a major challenge for all agricultural crops, but for rice, it is even more serious, because of its semi aquatic phylogenetic origins and the diversity of rice ecosystems and growing conditions. The most important source of climate-related risks for rice production in rain-fed areas is drought.Crop physiology has made a significant contribution to understanding the mechanisms underlying crop growth and development, and bridging the “phenotype gap” generated by the recent progress in genomics. The study aimed to determine growth and physiological response of IRAT 109 and Lemont to water deficit and fertilizer application. Plants were subjected to water nutrient stress treatment in the field. Water and fertilizer treatment were initiated at 42 days after sowing (das). Fertilizer treatment was applied at 60 Kgha-1N and 60 Kgha-1N+45 Kgha-1P. Morphological and physiological measurements were done at 21, 42, 63 and 84th das. Root sampling done during the periods, at depths of 0-10 cm, 10-20 cm, and 20-40 Cm. The soil moisture content had a significant effect and decreased with increasing water deficit. The plant height, plant biomass both shoots and root reduced with decreasing water content and nutrient load in the soil. Lemont was significantly affected and registered lower values for various growth indices compared to IRAT 109. The was significant reduction in yields between the two rice cultivars under drought stress condition, though IRAT 109 exhibited relatively higher yield index under drought stress condition, the improved performance could be attributed to its ability to escape drought stress due to its early maturing ability. Fertilizer application has a significant effect on yield and yield component in rice, thus the proper fertilizer application is a key in achieving good yield in rice production. The finding of this research will help farmers in adopting high precision fertilizer application to ensure a good yield. In addition, rice breeders can utilize IRAT109 in developing more resilient and highly adaptive rice cultivars.

Applying a process-based livestock model to predict spatial variation in agricultural nutrient flows in Scotland

Achieving an optimal nutrient balance is one of the main targets of sustainable agriculture. The aim of this study was to identify “hotspots” of agricultural nutrient imbalance. This was done by developing a modelling framework and using it to analyse the spatial distribution of agricultural nitrogen and phosphorus flows. The nutrient flows for the main livestock species in Scotland (namely cattle, sheep, pigs and chickens), were quantified using the Scottish Agricultural Emission Model (SAEM). The model was used in connection with agricultural census data for Scotland, which provided spatial distribution of the livestock production, including numbers of animals in certain livestock categories. The average fertiliser application rates for the main crops in Scotland were obtained from the British Survey of Fertiliser Practice and were used as an indicator of the nutrient demand for these crops. The Scottish agricultural census data were used to determine the spatial distribution of different arable crops and grassland in Scotland. This spatial information was combined with the nutrient excretion results to determine the nutrient balance. The results show that the areas with highest nitrogen fertiliser application rate are mainly located in central and eastern Scotland, including the areas where cereal production mainly occurs, while areas where the availability of excreted nutrients is highest are located in southern and north eastern Scotland, i.e. in the main cattle production areas. The higher stability of excreted phosphorus compared to nitrogen allowed a more detailed analysis of a regional phosphorus balance. In major parts of the agricultural production areas in eastern Scotland, the fertiliser application rate (crop nutrient demand) exceeds the amount of phosphorus excreted by the livestock. There are also areas where high phosphorus fertiliser application rate (crop production) and organic phosphorus output (from animal production) overlap, indicating that in these areas there is a high potential to re-use the phosphorus excreted by livestock. Compared to other spatial models for nutrient flows, the modelling framework utilizing a process-based livestock model provides scope to analyse the effects of livestock management and potential changes in livestock systems on regional nutrient balances in more detail.

Effects of N-fertilization and rootstocks on the performance of ‘Red Delicious’ Spur apple trees

In a field trial with the Spur variety Super Chief® Sandidge, three different levels of nitrogen supply (50, 100, 150 kg ha(-1)) in combination with 3 rootstocks (M9 at 8333 trees ha(-1), M26 at 5555 trees ha(-1) and Pi80 at 4166 trees ha(-1)) were compared with respect to soil nitrogen dynamics, leaf nutrient levels, tree vigour and yield. The experimental orchard was planted in 2007 and the trial lasted until 2014. The data collected in this period revealed no significant effect of nitrogen levels above 50 kg ha(-1) year-1 on tree vigour and fruit yield, whereas clear differences emerge with respect to the different planting systems (rootstock/planting density). The observed soil nitrogen dynamics indicate that a considerable amount of mineral nitrogen may be lost by leaching from the very permeable soil at the site of the experiment, in particular in the case of high fertilizer applications and humid climatic conditions. Leaf nitrogen contents were not significantly affected by fertilizer rates.

Forage Production and Economic Performance of Pasture Rejuvenation Methods in Northern Alberta, Canada

Producing high quality forage and maintaining productive pastures is a major challenge that beef producers encounter, as rejuvenation is a complex and costly challenge. This is part of a series of papers looking at potential options and methods of rejuvenation to improve the productivity of older forage stands in northern Alberta. The methods of rejuvenation investigated were sub-soiling, break & re-seeding, a combination of manure application plus subsoiling, high stock density grazing, bale grazing, pasture rest, as well as direct seeding in spring and fall. In this series, forage dry matter (DM) yield, forage nutritive value and economic performance are presented and discussed. The top 5 forage DM yielders were bale grazing, manure + subsoil in fall, break & re-seeding, high stock density grazing and fertilizer application in that order. In both years, bale grazing consistently produced higher forage DM yield than other methods including control, with bale grazing giving up to 100% higher yield at site-1 and 219% at site- 2 for the 2-year total forage DM. Most forage nutritive value parameters measured were similar for the rejuvenation methods investigated. A simplified economic analysis done in this study showed that the direct input cost of rejuvenation an old forage stand was higher with the break & re-seeding method than other methods. However, for bale grazing, when the cost of hay bales used was factored in, then the cost of bale grazing far exceeded those of other methods including break & re-seeding. The implications of the results obtained in this study in relation to beef cattle production system are highlighted.

Insect pollination as an agronomic input: Strategies for oilseed rape production

Abstract Ecological intensification involves the incorporation of biodiversity‐based ecosystem service management into farming systems in order to make crop production more sustainable and reduce reliance on anthropogenic inputs, including fertilizer and insecticides. The benefits of effectively managing ecosystem services such as pollination and pest regulation for improved yields have been demonstrated in a number of studies, however, recent evidence indicates that these benefits interact with conventional agronomic inputs such as fertilizer and irrigation. Despite the important contribution of biodiversity‐based ecosystem services to crop production their management is rarely considered in combination with more conventional agronomic inputs. This study combines a number of complementary approaches to evaluate the impact of insect pollination on yield parameters of Brassica napus and how this interacts with a key agronomic input, fertilizer. We incorporate data from a flight cage trial and multiple field studies to quantify the relationships between yield parameters to determine whether insufficient insect pollination may limit crop yield. We demonstrate that, by producing larger seeds and more pods, B. napus has the capacity to modulate investment across yield parameters and buffer sub‐optimal inputs of fertilizer or pollination. However, only when fertilizer is not limiting can the crop benefit from insect pollination, with yield increases due to insect pollination only seen under high fertilizer application. A nonlinear relationship between seed set per pod and yield per plant was found, with increases in seed set between 15 and 25 seeds per pod resulting in a consistent increase in crop yield. The capacity for the crop to compensate for lower seed set due to sub‐optimal pollination is therefore limited. Synthesis and applications. Oilseed rape has the capacity to compensate for sub‐optimal agronomic or ecosystem service inputs although this has limitations. Insect pollination can increase seed set and so there are production benefits to be gained through effective management of wild pollinators or by utilizing managed species. Our study demonstrates, however, that increased insect pollination cannot simply replace other inputs, and if resources such as fertilizer are limiting, then yield potential cannot be reached. We highlight the need to consider insect pollination as an agronomic input to be effectively managed in agricultural systems.

Effects of different fertilization regimes on nitrogen and phosphorus losses by surface runoff and bacterial community in a vegetable soil

Vegetables are major economic crops in China. Their cultivation usually involves high fertilizer application rates leading to significant losses of N and P to the wider environment, resulting in water contamination and low nutrient use efficiency. Hence, it is a matter of urgency to understand the mechanisms and factors that affect N and P losses in vegetable production systems in order to develop optimum fertilization regimes. Different fertilization regimes were applied in a long-term chili (Capsicum spp. L.) production soil to study the effects on nitrogen (N) and phosphorus (P) runoff losses, microbial biomass, microbial community, and crop yields. Three fertilization regimes were implemented: control (no fertilizer; CK), farmer’s fertilization practice (FFP), and site-specific nutrient management (SSNM). A fixed collection device was used to quantify the total volume of water output after each precipitation event. All water samples were analyzed for total nitrogen, ammonium nitrogen (NH4+-N), nitrate nitrogen (NO3−-N), total phosphorus (TP), and available phosphorus (AP). Soil samples were collected for analysis of the physicochemical properties and for DNA extraction after chili harvest. High-throughput sequencing was used to further investigate the relationship between the microbial community and nutrient losses. The SSNM fertilizer regime resulted in a 23.3% yield increase and enhanced agronomic N use efficiency from 11.87 to 15.67% compared with the FFP treatment. Soil available nutrients (i.e., AN and AP) and ATP content increased significantly after SSNM implementation. Under the SSNM regime, N losses decreased by 25.8% compared with FFP but did not lead to significantly different P losses. High-throughput sequencing results showed that each treatment formed a unique microbial community structure. VPA results revealed that the microbial community structure was mainly (50.56%) affected by the interactions between N and P. Mantel results indicated that the soil properties that significantly affected soil microbial community structure followed the order: AP, AK, and salinity. Our study has demonstrated that SSNM not only generates lower N losses but also provides higher contents of soil available nutrients and plant yield, which were mainly attributed to the multiple top dressings and meeting of the plants’ demand with adequate nutrient supplies. The combined data showed that the microbial community differentiation between the different fertilizer regimes was mainly linked to the interactions between N and P in the soil.

Potassium relative ratio to nitrogen considerably favors carbon metabolism in late-planted cotton at high planting density

A new planting model characterized with late sowing, high planting density, low N and single fertilizer application is much competitive to combat the present high cost cotton production. However, what is the optimal relative ratio of K to N under this model? as we understand it certainly plays a critical role in cotton production through a series of physiological processes. A two year (2016–2017) field experiment was conducted in a randomized complete block design with three K ratios relative to N [0.8 (K1), 1.0 (K2), and 1.2 (K3)] with four replications. Results showed that relative increase in K ratio had significant effect on functional leaf biomass, specific leaf weight, carbon metabolism as well as cotton yield in both growing seasons. K3 and K2 produced the similar seed cotton yield but higher than K1 in both years. Similarly, K3 and K2 prominently up-regulated the activity of ribulose 1, 5-bisphosphate carboxylase oxygenase (Rubisco), sucrose phosphate synthase (SPS) and sucrose synthase (SS) but down-regulated the activity of soluble acid invertase (SAI), glucose-6-phosphate dehydrogenase (G6PDH) and 6-phosphogluconate dehydrogenase (6PGDH). Moreover, the balance of carbohydrates (sucrose, starch, glucose and fructose) and ATP was more efficient under higher K ratio (K3 and K2) as compared with K1. These findings might suggest that K rate should be equal to N as for promising yield and profitable return are concerned under newly proposed cotton planting model in the Yangtze River Valley of China.

Yield loss management through fertilizers in Banana bract mosaic virus affected French plantain cv. Nendran (AAB)

Plant virus infection significantly reduces the yield of many horticultural crops causing reduction in the production and productivity. Higher fertilizer application has often to overcome the yield reduction due to virus in many crops. A field experiment was conducted to find out the effect of increased doses of fertilizers on the banana bract mosaic virus (BBrMV) infected plants of French plantain cv. Nendran. The plant height, girth, number of leaves, number of fingers and the bunch weight had significantly increased with increased dose of fertilizer in the first and second crops with BBrMV infection. In the first crop, with the application of 125 and 150% of recommended dose of fertilizers (RDF), the BBrMV infected plants could produce bunches which were on par with that of healthy plants, receiving 100% RDF, but with prolonged days of flowering. In the second crop, though 125 and 150% RDF doses in the infected plants increased the bunch weight over 100% RDF by 14.60% and 18.33%, respectively, could not be able to compensate the yield loss due to virus infection. This may probably be due to the accumulation of virus over the period of two years. This is the first report on strategies for mitigating adverse effects of BBrMV in plantain.

Different Response Patterns of Soil Respiration to a Nitrogen Addition Gradient in Four Types of Land-Use on an Alluvial Island in China

It has been well documented that nitrogen (N) additions significantly affect soil respiration (R s) and its components [that is, autotrophic (R a) and heterotrophic respiration (R h)] in terrestrial ecosystems. These N-induced effects largely result from changes in plant growth, soil properties (for example, pH), and/ or microbial community. However, how R s and its components respond to N addition gradients from low to high fertilizer application rates and what the differences are in diverse land-use types remain unclear. In our study, a field experiment was conducted to examine response patterns of R s to a N addition gradient at four levels (0, 15, 30, and 45 g N m−2 y−1) in four types of land-use (paddy rice–wheat and maize–wheat croplands, an abandoned field grassland, and a Metasequoia plantation) from December 2012 to September 2014 in eastern China. Our results showed that N addition significantly stimulated R s in all four land-use types and R h in croplands (paddy rice–wheat and maize–wheat). R s increased linearly with N addition rates in croplands and the plantation, whereas in grassland, it exhibited a parabolic response to N addition rates with the highest values at the moderate N level in spite of the homogeneous matrix for all four land-use types. This suggested higher response thresholds of R s to the N addition gradient in croplands and the plantation. During the wheat-growing season in the two croplands, R h also displayed linear increases with rising N addition rates. Interestingly, N addition significantly decreased the apparent temperature sensitivity of R s and increased basal R s. The different response patterns of R s to the N addition gradient in diverse land-use types with a similar soil matrix indicate that vegetation type is very important in regulating terrestrial C cycle feedback to climate change under N deposition.

Grazing and Soil Fertility Effect on Naturalized Annual Clover Species in New Zealand High Country

With a view to increasing rangeland pasture legume abundance, the herbage biomass and seedling recruitment of four New Zealand naturalized annual clover species (haresfoot clover Trifolium arvense L., suckling clover T. dubium Sibth, cluster clover T. glomeratum L., and striated clover T. striatum L.) were measured in relation to spring grazing deferment versus continuous grazing and low versus high superphosphate fertilizer application (5 vs. 9 kg P · ha–1) at a midaltitude (700-m) hill site. Naturalized species were dominant over periodically sown white (T. repens L.) and subterranean clover (T. subterraneum L.), contributing > 90% to sward legume composition. Rainfall in spring–early summer varied greatly between years, driving the large variation in sward legume content (28% in the moist first year; 2% in the very dry second year). Grazing deferment in spring did not influence autumn seedling recruitment or the following spring herbage biomass of naturalized species. However, autumn recruitment of naturalized clovers was greater under low fertilizer (563 seedlings · m–2) compared with high fertilizer application (271 seedlings · m–2) in the second year of the study, suggesting a niche for these species under conditions of low soil P and S. Management efforts should focus on strategies to enhance naturalized species spread within NZ rangeland.

Estimating the gross budget of applied nitrogen and phosphorus in tea plantations

Abstract To increase crop yield, high fertilizer application rates have generally been used. The residual fertilizers potentially become a source of diffused pollution, and degrade soil and water quality. Such nonpoint source pollution is a major threat to reservoir eutrophication. The best management practices (BMPs) are usually used to prevent eutrophication; however, the environmental distribution of the applied fertilizers has not been understood properly. This could lead to a biased assessment of the rational quantity of nitrogen and phosphorous applied and the selection of BMPs. A field investigation of 32 plantations and 4 forests in the Feitsui Reservoir watershed, Taiwan, was conducted. Storm runoff water and soils were sampled, and a mass balance was used to demonstrate the gross nutrient budget. The results showed that when applying fertilizers of 2700 kg ha−1 in tea plantations only 18.3% of applied nitrogen and 5.5% of applied phosphorus were utilized by tea plants. Less than 5% of applied phosphorus was released in storm runoff, and more than 90% remained in the field. Approximately 30% of the nitrogen was lost through storm runoff, and 52% was stored in the soil mass. Therefore, reducing fertilizer application was recommended as the principal BMP, and collecting and treating storm runoff was suggested for controlling nitrogen pollution. The current management of soil erosion is an efficient measure for controlling phosphorus pollution.

Risk assessment of shallow groundwater contamination under irrigation and fertilization conditions

Due to extensive agricultural irrigation and fertilization, China now faces a severe problem of non-point source groundwater contamination. In this paper, the Daxing district of Beijing, a typical agricultural area with high fertilizer application, is chosen as the study area. With the consideration of intrinsic vulnerability and nitrate contamination load of groundwater, DRASTIC-based methodology was used to establish a GIS-based groundwater contamination risk assessment model, namely DRSIN model. The DRSIN model contains five parameters: depth to groundwater (D), net recharge (R), soil type (S), impact of the vadose zone (I) and nitrogen (N). By employing cluster analysis and fuzzy synthetic evaluation, the influence of agricultural non-point source contamination of groundwater on the formation of nitrate contamination was discussed under the existing conditions and 11 different irrigation and fertilization scenarios. The results show that the groundwater contamination risk in the north and east of Daxing District is higher than that in the south and the west, which conforms to the monitoring results of nitrate nitrogen content in groundwater. This indicates the need for reasonable groundwater utilization and protection planning to reduce agricultural non-point source contamination. Groundwater contamination risk decreases most significantly under the scenario of irrigation amount reduced by 25 %, nitrogen application reduced by 25 % and groundwater depth increased by 5 m. The findings provide data for reasonable groundwater development and utilization in this area.

Overwintering Survival and Vigor of Container-grown Fountain Grass: Influence of Substrate Moisture Content, Protective Covers, and Fertilizer Rate

Despite the popularity of fountain grass (Pennisetum alopecuroides) as a landscape perennial, little research has been conducted on nursery management practices that maximize its overwintering survival and subsequent spring vigor in container production systems. An experiment was conducted to determine the effect of protective covers (a double layer of insulation fabric, a double layer of insulation fabric plus a single sheet of white polyethylene plastic, or no cover), fertilizer application rate (high and low), and substrate moisture content (irrigated when substrate volumetric water content (VWC) fell below 15% and 25%) on the survival rate and vigor of container-grown fountain grass: straight species fountain grass (SFG), ‘Hameln’ fountain grass (HFG), and ‘Little Bunny’ fountain grass (LBFG). Plants were overwintered in a coldframe and were evaluated for survival rate (percent that survived the winter) and vigor (visual rating scale 1 to 5) the following spring. Survival rate and vigor ratings varied among species. However, the highest survival rates (generally 75% or greater) and vigor ratings (generally 3 or greater) were in treatments that used protective covers, though there was not a clear advantage to using white polyethylene in addition to the double layer of insulation fabric. In treatments that used either of the protective covering methods and the high fertilizer application rate, 25% or less of LBFG survived and had vigor ratings of 1.3 or less. In contrast, 75% of LBFG survived when the low fertilizer rate was used in conjunction with either protective covering method. Substrate moisture content only affected the survival rates of SFG and HFG when no protective cover was used, although these survival rates were less than those with covers. These results suggest that protective covers may serve as a tool to minimize winter damage and improve crop quality for the species used in this trial. Because of the varied capacity among these cultivars to tolerate different fertilizer rates and substrate moisture contents, it is recommended that growers use the results of this study as a baseline for conducting site evaluations to determine overwintering techniques that maximize survival and vigor on their facilities.

Mulching and Fertilization Effects on Weed Dynamics under Conservation Agriculture-Based Maize Cropping in Zimbabwe

A two-year study was conducted to assess how mulch influences weed dynamics following imposition of different fertilization treatments under three crop establishment options: (i) conventional; (ii) ripping; and (iii) basin, in a two-year maize-legume rotation. Eight treatments were imposed within each crop establishment option and received maize stover mulch applied at 0% or 30% cover before planting maize (Zea mays) or cowpea (Vigna unguiculata) as test crops. Maize received nitrogen (N) at 35, 90, or 120 kg·ha−1 and phosphorus (P) at 14 or 26 kg·ha−1 applied alone or in combination with 4 or 7 t cattle manure·ha−1, while cowpea received 8 or 17 N·kg·ha−1 and similar P rates to maize. Results indicated that both weed biomass and diversity were influenced more by fertilization than method of crop establishment. On treatments under high fertilizer application rates, or previously planted to cowpea weed biomass ranged between 220 and 400 g·m−2 under mulch and 370–510 g·m−2 (no mulch). Here species richness ranged between 7–16 and was dominated by dicotyledons. This was in contrast to biomass ranges of 75–200 g·m−2 in the low fertilized and control plots, where only one or two grass types dominated. Overall, weed densities were 6% to 51% higher under conventional tillage compared to the two conservation agriculture (CA) options, although the data indicated that mulch significantly (p < 0.05) depressed weed density by up to 70%. We concluded that mulching could be a potential mechanism for reducing weeding labor costs for smallholders and the general environmental and health concerns associated with the use of herbicides in CA systems.

The core root microbiome of sugarcanes cultivated under varying nitrogen fertilizer application.

Diazotrophic bacteria potentially supply substantial amounts of biologically fixed nitrogen to crops, but their occurrence may be suppressed by high nitrogen fertilizer application. Here, we explored the impact of high nitrogen fertilizer rates on the presence of diazotrophs in field-grown sugarcane with industry-standard or reduced nitrogen fertilizer application. Despite large differences in soil microbial communities between test sites, a core sugarcane root microbiome was identified. The sugarcane root-enriched core taxa overlap with those of Arabidopsis thaliana raising the possibility that certain bacterial families have had long association with plants. Reduced nitrogen fertilizer application had remarkably little effect on the core root microbiome and did not increase the relative abundance of root-associated diazotrophs or nif gene counts. Correspondingly, low nitrogen fertilizer crops had lower biomass and nitrogen content, reflecting a lack of major input of biologically fixed nitrogen, indicating that manipulating nitrogen fertilizer rates does not improve sugarcane yields by enriching diazotrophic populations under the test conditions. Standard nitrogen fertilizer crops had improved biomass and nitrogen content, and corresponding soils had higher abundances of nitrification and denitrification genes. These findings highlight that achieving a balance in maximizing crop yields and minimizing nutrient pollution associated with nitrogen fertilizer application requires understanding of how microbial communities respond to fertilizer use.

Yield gap analysis and resource footprints of Irish potato production systems in Zimbabwe

Irish potato is the third most important carbohydrate food crop in Zimbabwe after maize and wheat. In 2012, the Government of Zimbabwe declared it a strategic national food security crop. In this study, we examine the country's potential for increasing Irish potato yield and help ease the nation's food security challenges. The magnitude of food production increase on already existing croplands depends on the difference between the current actual yields and the potential yield of the crop in the given agro-ecological environment, also called the yield gap. We used three already well-understood types of yield gap: (1) the gap between actual farmer yields, Ya, and the maximum (potential) yield, Yp, achieved when a crop is grown under conditions of non-limiting water and nutrient supply with biotic stress effectively controlled; (2) the gap between Ya and the water-limited yield, Yw, which is the maximum yield attainable under rainfed systems; and (3) the gap between Ya, and the highest yield, Yh, achieved by the best farmers in an agro-ecological area. A grower survey was conducted on the different potato production systems in the country in order to establish the actual yields and input application rates used in potato production. The actual potato yields were used to calculate efficiencies of natural and synthetic resources use. Potential and water-limited yields, and planting times of potato were established for the different agro-ecological regions using the LINTUL-POTATO model, a model based on interception and utilisation of incoming solar radiation. The mean actual yield observed ranged from 8 to 35% of the potential yield, translating to a yield gap of 65 to 92%, hence there is a huge potential to increase production. Simulated potential water use efficiency based on evapotranspiration range was 19–27gpotato/l against the actual water use efficiency of 2–6gpotato/l based on irrigation and rainfall. The current high fertiliser application rates and low actual yields we report, suggest inefficient fertiliser use in potato production in Zimbabwe. The average actual fungicide and insecticide use efficiencies were 0.7 and 13kgpotato/g active ingredient, respectively, across all production systems. All sampled growers lacked knowledge on integrated pest management, a concept which could possibly improve the biocide use efficiency through lowering biocide application rates while maintaining or even improving yields. Our analysis suggests that there is opportunity to improve water, nutrients and biocides resource use efficiencies and increase potato actual yields in Zimbabwe.

Urine patch and fertiliser N interaction: Effects of fertiliser rate and season of urine application on nitrate leaching and pasture N uptake

Urine patches are the primary source of N loss from pastoral systems due to the high N loading that occurs over a relatively small area. However, few studies have sought to determine the effect of concurrently deposited urine and fertiliser on the fate of N in pastoral systems, even though the application of fertiliser soon after grazing is commonly practised, while no studies have examined seasonal effects of any interaction.The objective of this study was therefore, to understand how the combination of fertiliser-N and urine affected fertiliser-associated NO3− leaching losses and plant uptake of N. A two year lysimeter study was undertaken with urine (800kg Nha−1) applied in either autumn or spring. Urea fertiliser enriched with 15N was applied to these lysimeters at rates equivalent to 200 or 400kg Nha−1 per year according to the standard regional practice.Urine and fertiliser at the 400kg Nha−1 rate increased total NO3− leaching by up to 58kgha−1 (P<0.001), from urine applied in either autumn or spring. Fertiliser applied at 200kg Nha−1 did not increase N leaching from urine patches. Fertiliser 15N recovery in drainage was <2.2% and was not affected by fertiliser rate. Pasture uptake accounted for up to 52% of the fertiliser 15N recovery and this increased with increasing fertiliser rates, even in the presence of urine. Recovery of fertiliser 15N in the soil at the end of the experiment averaged 22% with the majority of this in the top 10cm soil.These results indicate that the potential for leaching of fertiliser N, applied to a urine patch, is low, and that avoiding fertiliser application over urine patches, reduces leaching losses of fertiliser-N by <2%, which is minimal in terms of total N loss mitigation. However, at high fertiliser application rates to urine patches (i.e. 400kg Nha−1), the total N leaching from non-fertiliser (non 15N-enriched) sources can increase. Further work is required to quantify these effects at the paddock scale. The results also show that NO3− leaching losses were greater from autumn applied urine compared to spring applied urine by up to 306kg NO3−-Nha−1.

First Report of Sheath Blight Caused by Waitea circinata Affecting Foxtail Millet (Setaria italica) in China

Foxtail millet (Setaria italica) is planted widely in northern China, especially in Hebei, Shanxi, Shandong, and Henan provinces. Although several diseases reduce production of this important crop species, sheath blight is considered one of the important diseases of foxtail millet in China. Sheath blight is caused by a soil-borne pathogen and is difficult to control. Epidemics are most common at the late growth stage of foxtail millet. In August 2013, an outbreak was recorded in Shijiazhuang city, Hebei, with an incidence of about 60%. Typical disease symptoms consisted of large, irregular lesions with reddish-brown margin and as the disease progressed, the plants lodge. Three representative sheath fragments (each 1 cm long) were collected from diseased plants during that outbreak. The samples were disinfected with 0.5% (v/v) sodium hypochlorite, rinsed with sterile water, placed on a water agar plate, and then incubated at 26°C in the dark for two days. After the hyphae appeared, ~3-mm-long hyphal tips from typical colonies were excised and transferred to potato dextrose agar (PDA) plates. Three isolates were obtained and all showed typical features of Rhizoctonia-like fungus. Each isolate occupied its whole plate within 5 days of incubation at 26°C in the dark, and abundant aerial mycelia were produced. The color of all colonies was first orange, turning a salmon color when the mycelia matured. Orange sclerotia appeared after 2 weeks of incubation. The nuclei were stained with DAPI (2-(4-amidinophenyl)-1H-indole-6-carboxamidine) and observed under a fluorescent microscope. The hyphal cells were multinucleate and the mycelia branched at a right angle. For molecular identification of the pathogen, mycelia of each isolate were cultured in potato dextrose broth at 26°C for a week, and genomic DNA was extracted from mycelia and used as a template for PCR amplification. The primers set of ITS1 and ITS4 was used for amplification of rDNA-ITS from these isolates and the amplified rDNA-ITS regions of all isolates (GenBank Accession Nos. KJ765700, KJ765701, and KJ765702, respectively) were 99% identical to other Waitea circinata deposited in GenBank (1,2). To further confirm the pathogenicity of the isolates, freshly collected PDA plugs were inoculated on the lower leaf blades of 8-week-old seedlings of the foxtail millet variety Yugu 1. PDA plugs without the isolate were used as a negative control. Five plants were used for each isolate and negative control. After inoculation, pots were placed together in a moist chamber at 26°C. No symptoms developed on the control plants, while obvious lesions appeared on the sheaths of tested plants at 5 days post inoculation and later the plants were lodging. The fungus was re-isolated from diseased plants and confirmed to be W. circinata based on morphological characteristics and sequence analysis as previously described, completing Koch's postulates. Further, on the basis of morphological tests, pathogenicity assays, and molecular analyses, the pathogen of foxtail millet sheath blight was identified as W. circinata (4). Although Rhizoctonia solani AG-1, AG-4 has been reported in earlier studies as the pathogen causing foxtail millet sheath blight, there has been no previous report of the disease caused by W. circinata (3). To our knowledge, this is the first report of foxtail millet sheath blight caused by W. circinata in China. With the spread of high millet plant density and fertilizer application, this disease may become a major threat to foxtail millet; therefore, W. circinata should be taken into account when designing measures for disease control in foxtail millet.