Irrigation and nitrogen fertiliser optimisation in protected vegetable fields of northern China:Achieving environmental and agronomic sustainability

Globally,sub-optimal use of nitrogen (N) fertiliser and elevated N irrigation groundwater have led to high leached nitrate (NO_(3)^(–)) losses from protected vegetable field systems.Optimising fertiliser and irrigation management in different soil types is crucial to reduce future N loads from such systems.The present 4-year study examined leached N loads from lysimeter monitoring arrays set up across 18 protected vegetable system sites encompassing the dominant soil types of northern China.The treatments applied at each field site were:1) a high N and high irrigation input treatment (HNHI);2) a low N but high irrigation input treatment (LNHI) and 3) a low N with low irrigation input treatment (LNLI).Results showed that the mean annual leached total nitrogen loads from the HNHI,LNHI and LNLI treatments were 325,294 and 257 kg N ha^(–1) in the fluvo-aquic soil,114,100 and 78 kg N ha^(–1) in the cinnamon soil and 79,68 and 57 kg N ha^(–1) in the black soil,respectively.The N dissolved in irrigation water in the fluvo-aquic soil areas was 8.26-fold higher than in the cinnamon areas.A structural equation model showed that N fertiliser inputs and leaching water amounts explained 14.7 and 81.8%of the variation of leached N loads,respectively.Correspondingly,reducing irrigation water by 21.5%decreased leached N loads by 20.9%,while reducing manure N and chemical N inputs by 22 and 25%decreased leached N loads by only 9.5%. This study highlights that protected vegetable fields dominated by fluvo-aquic soil need management to curtail leached N losses in northern China.

Evaluation of Parametric Limitations in Simulating Greenhouse Gas Fluxes from Irish Arable Soils Using Three Process-Based Models

Globally a large number of process-based models have been assessed for quantification of agricultural greenhouse gas (GHG) emissions. Modelling approaches minimize the presence of spatial variability of biogeochemical processes, leading to improved estimates of GHGs as well as identifying mitigation and policy options. The comparative performance of the three dynamic models (e.g., DNDC v9.4, DailyDayCent and ECOSSE v5+) with minimum numbers of common input parameters was evaluated against measured variables. Simulations were performed on conventionally-tilled spring barley crops receiving N fertilizer at 135 - 159 kg·N·ha-1·yr-1 and crop residues at 3 t·ha-1·yr-1. For surface soil nitrate (0 - 10 cm), the ECOSSE and DNDC simulated values showed significant correlations with measured values (R2 = 0.31 - 0.55, p 0.05). Only the ECOSSE-simulated N2O fluxes showed a significant relationship (R2 = 0.33, p 0.05) with values measured from fertilized fields, but not with unfertilized ones. The DNDC and DailyDayCent models significantly underestimated seasonal/annual N2O fluxes compared to ECOSSE, with emission factors (EFs), based on an 8-year average, were 0.09%, 0.31% and 0.52%, respectively. Predictions of ecosystem respiration by both DailyDayCent and DNDC showed reasonable agreement with Eddy Covariance data (R2 = 0.34 - 0.41, p 0.05). Compared to the measured value (3624 kg·C·ha-1·yr-1), the ECOSSE underestimated annual heterotrophic respiration by 7% but this was smaller than the DNDC (50%) and DailyDayCent (24%) estimates. All models simulated CH4 uptake we

A comparison of the nutritive value of perennial ryegrass,perennial ryegrass and white clover and multispecies-based farmlet systems

Background:Limited information is available regarding the nutritive value and structural characteristics of multispecies swards when rotationally grazed.Methods:Three farmlet types were investigated in terms of their nutritive value:Lolium perenne(LP);L.perenne+Trifolium repens(LP+TR);and a multispecies sward containing grasses,legumes and herbs(MSS).Farmlets were stocked with beef steers(2.5 livestock units ha−1),grazed on a 1 ha scale to 6 cm(MSS)and 4 cm(LP and LP+TR)residuals.Results:A greater ash concentration was found in MSS than LP(84 vs.75 g kg−1 DM).Both LP+TR and MSS had higher crude protein and lower neutral detergent fibre concentrations than LP.The relative ranking of water soluble carbohydrate and dry matter(DM)concentration was LP>LP+TR>MSS.Despite the leaf component of the LP farmlet contributing more to herbage DM,the organic matter digestibilities of the swards were similar.Conclusions:The MSS and LP+TR farmlets achieved similar forage quality under intensive grazing to LP.However,it is worth noting that MSS had a higher concentration of acid detergent lignin,which can negatively impact digestibility.Further investigation is needed to determine optimal grazing management practices that can minimise the effects of higher lignin concentration on digestibility in multispecies swards.

Annual yields of multispecies grassland mesocosms outperformed monocultures across a drought gradient due to complementarity effects and rapid recovery

Background:More frequent and severe drought events due to climate change pose a major challenge for sustainable forage production in managed grasslands.This study investigated whether multispecies grassland communities can provide greater resistance to and/or recovery from drought compared to monoculture communities.Methods:Mesocosms of Lolium perenne L.,Cichorium intybus L.,Trifolium repens L.and Trifolium pratense L.were established as monocultures,and a four-species mixture.A drought gradient with five levels of water supply ranging from a mild to a severe treatment was applied for 10 weeks,in each of 2 years.Shoot biomass was harvested to assess drought resistance,drought recovery and annual yields.Root mass density and specific root length were measured in Year 2.Results:Across the drought gradient,four-species communities had significantly larger annual yields than each of the four monocultures,indicating transgressive overyielding.This was despite relatively low drought resistance for four-species communities compared with L.perenne and C.intybus monocultures.Recovery of yields following drought was high for all communities.Conclusions:Multispecies swards with complementary traits can provide a viable adaptation option across a wide range of drought severities.Application of a stress gradient methodology allowed a more detailed understanding of stress responses.

C:N:P stoichiometry and nutrient limitation of the soil microbial biomass in a grazed grassland site under experimental P limitation or exces

Introduction:The availability of essential nutrients,such as nitrogen(N)and phosphorus(P),can feedback on soil carbon(C)and the soil microbial biomass.Natural cycles can be supplemented by agricultural fertiliser addition,and we determined whether the stoichiometry and nutrient limitation of the microbial biomass could be affected by an unbalanced nutrient supply.Methods:Samples were taken from a long-term trial(in effect since 1968)with annual applications of 0,15 and 30 kg P ha^(−1) with constant N and potassium.Soil and microbial biomass CNP contents were measured and nutrient limitation assessed by substrate-induced respiration.Linear regression and discriminant analyses were used to identify the variables explaining nutrient limitation.Results:Soil and biomass CNP increased with increasing P fertiliser,and there was a significant,positive,correlation between microbial biomass P and biomass C,apart from at the highest level of P fertilisation when the microbial biomass was over-saturated with P.The molar ratios of C:N:P in the microbial biomass remained constant(homeostatic)despite large changes in the soil nutrient ratios.Microbial growth was generally limited by C and N,except in soil with no added P when C and P were the main limiting nutrients.C,N and P,however,did not explain all the growth limitation on the soils with no added P.Conclusions:Increased soil C and N were probably due to increased net primary production.Our results confirm that C:N:P ratios within the microbial biomass were constrained(i.e.homeostatic)under near optimum soil conditions.Soils with no added P were characterised by strong microbial P limitation and soils under high P by over-saturation of microorganisms with P.Relative changes in biomass C:P can be indicative of nutrient limitation within a site.

Alum split applications strengthened phosphorus fixation and phosphate sorption in high legacy phosphorus calcareous soil

High phosphorus(P)saturation arising from historic P inputs to protected vegetable fields(PVFs)drives high P mobilisation to waterbodies.Amendment of soils with alum has shown potential in terms of fixing labile P and protecting water quality.The present 15 month pot experiment investigated P stabilisation across single alum application(Alum-1 treatment,20 g alum/kg soil incorporated into soil before the maize was sown),alum split applications(Alum-4 treatment,5 g alum/kg soil incorporated into soil before each crop was sown i.e.4×5 g/kg)and soil only treatment(Control).Results showed that the Alum-1 treatment caused the strongest stabilisation of soil labile P after maize plant removal,whereas the P stabilisation effect was gradually weakened due to the transformation of soil non-labile P to labile P and the reduced active Al^(3+)in soil solution.For the Alum-4 treatment,soil labile P decreased gradually with each crop planting and was lower than the Alum-1 treatment at the end of the final crop removal,without any impairment on plant growth.The better P stabilisation at the end of Alum-4 treatment was closely correlated with a progressive supply of Al^(3+)and a gradual decrease of pH,which resulted in higher contents of poorlycrystalline Al,Fe and exchangeable Ca.These aspects were conducive to increasing the soil P stabilisation and phosphate sorption.In terms of management,growers in continuous cropping systems could utilise split alum applications as a strategy to alleviate P losses in high-P enriched calcareous soil.

Variability of water supply affected shoot biomass and root depth distribution of four temperate grassland species in monocultures and mixtures

Aims Research on the effects of extreme rainfall events on ecosystem function has primarily focussed on drought or flooding events,which usually include changes to mean or total rainfall,annually or over a season.However,less is known about the effects of increased rainfall variability without change to mean or total amounts.We investigated the effects of increased variation of water supply on shoot and root biomass as well as the distribution of root biomass of four grassland plant species,grown in monoculture and mixture communities.Methods Perennial ryegrass(Lolium perenne L.,shallow-rooting grass),chicory(Cichorium intybus L.,deep-rooting forb),white clover(Trifolium repens L.,shallow-rooting legume)and red clover(Trifolium pratense L.,deep-rooting legume)were established in mesocosms.Four plants of the same species were grown in monoculture communities and one of each species grown in four-species communities.Water supply was manipulated such that;compared with a baseline level with low variation in water supply,there was a treatment with medium variation(±40%)and another with high variation(±80%).Shoot and root biomass were measured,and vertical root distribution models fitted.Important Findings Compared with the low variation treatment,shoot biomass was significantly reduced under high variation for white clover,red clover and four-species communities.Under all conditions,four-species communities produced more shoot and root biomass than predicted by species performance in monoculture(overyielding).Under increased water variation,chicory monocultures allocated a higher proportion of root biomass to deeper soil layers while the total root biomass of white clover monocultures was significantly reduced.These results indicate that increased variability of water supply can negatively affect the shoot and root biomass production of single and multi-species grasslands.There is a need for further investigation of water variation effects on the functioning of multi-species grassland systems at field scale.