Effects of short-term nitrogen and phosphorus addition on leaf stoichiometry of a dominant alpine grass

The effects of increasing nitrogen (N) and phosphorus (P) deposition on the nutrient stoichiometry of soil and plant are gaining improving recognition. However, whether and how the responses of N cycle coupled with P of the soil–plant system to external N and P deposition in alpine grassland is still unclear. A short-term external N and P addition experiment was conducted in an alpine grazing grassland in the KunLun Mountain to explore the effects of short-term N and P addition on the nutrient stoichiometry in soil and plant. Different rates of N addition (ranging from 0.5 g N m−2 yr−1 to 24 g N m−2 yr−1) and P addition (ranging from 0.05 g N m−2 yr−1 to 3.2 g P m−2 yr−1) were supplied, and the soil available N, P, leaf N and P stoichiometry of Seriphidium rhodanthum which dominant in the alpine ecosystem were measured. Results showed that N addition increased soil inorganic N, leaf C, leaf N, and leaf N:P ratio but decreased soil available P and leaf C:P. Furthermore, P addition increased soil available P, leaf P, soil inorganic N, leaf N, and leaf C and reduced leaf C:N, C:P, and N:P ratios. Leaf N:P was positively related to N addition gradient. Leaf C:P and leaf N:P were significantly negatively related to P addition gradient. Although external N and P addition changed the value of leaf N:P, the ratio was always lower than 16 in all treatments. The influences of P addition on soil and plant mainly caused the increase in soil available P concentration. In addition, the N and P cycles in the soil–plant system were tightly coupled in P addition but decoupled in N addition condition. The nutrient stoichiometry of soil and leaf responded differently to continuous N and P addition gradients. These data suggested that the alpine grazing grassland was limited by P rather than N due to long-term N deposition and uniform fertilization. Moreover, increasing P addition alleviated P limitation. Therefore, the imbalanced N and P input could change the strategy of nutrient use of the grass and then change the rates of nutrient cycling in the alpine grassland ecosystem in the future.

Amendment Properties Affect Crop Performance, Leaf Tissue Nitrogen, and Soil Nitrogen Availability Following Soil Treatment by Anaerobic Soil Disinfestation

Efficacy of anaerobic soil disinfestation (ASD) for soilborne plant pathogen suppression is strongly influenced by soil environment and organic amendment attributes. At the same time, these factors influence soil nutrient availability, crop nutrition, and crop performance, but published information on ASD amendment property effects, including carbon to nitrogen (C:N) ratio and C substrate bioavailability, on crop performance and soil nutrient availability is limited. We evaluated ASD amendment effects on soil N availability, crop N status, and solanaceous crop performance in a series of trials: (1) greenhouse/growth chamber study of amendments (primarily molasses/soybean hulls and wheat bran) formulated at 10:1, 20:1, 30:1 and 40:1 C:N ratios (4 mg C g−1 soil), (2) field study with molasses/soybean hull-based amendments at equivalent C:N ratios/C rates (3) on-farm study with molasses/soybean hull-based amendments (4 mg C g−1 soil) compared to grower-standard control, and (4) field study of labile to recalcitrant amendment substrates at 30:1 C:N ratio (~3.4 mg C g−1 soil). ASD amendment C:N ratio strongly influenced soil inorganic N and the lowest (10:1) ratio was associated with highest soil inorganic N at ASD treatment termination in both trials 1 and 2, which often persisted into the cropping phase. Accordingly, the lowest amendment C:N ratio was also associated with the highest biomass (trail 1), leaf tissue N (trial 2), and crop yield (trials 1, 2) among treatments, even with application of recommended fertigation rates to all treatments in the field study. In trial 3, ASD treatment induced higher soil inorganic N and crop yield than the control, but no differences were observed in plant tissue N. In trial 4, more decomposable ASD substrates reduced soil inorganic N at ASD treatment termination, with the highest soil inorganic N associated with the most recalcitrant amendment, but there was no effect on crop yield. ASD amendment C:N ratio, and to a lesser extent, amendment decomposability, exert a strong influence soil inorganic N and crop performance. Optimization of ASD treatments for disease management will require simultaneous optimization of crop nutrition practices to facilitate more holistic, less confounded assessment of crop performance and to facilitate recommendations for grower adoption.

Organic Wastes Amended with Sorbents Reduce N2O Emissions from Sugarcane Cropping

Nutrient-rich organic wastes and soil ameliorants can benefit crop performance and soil health but can also prevent crop nutrient sufficiency or increase greenhouse gas emissions. We hypothesised that nitrogen (N)-rich agricultural waste (poultry litter) amended with sorbents (bentonite clay or biochar) or compost (high C/N ratio) attenuates the concentration of inorganic nitrogen (N) in soil and reduces emissions of nitrous oxide (N2O). We tested this hypothesis with a field experiment conducted on a commercial sugarcane farm, using in vitro incubations. Treatments received 160 kg N ha−1, either from mineral fertiliser or poultry litter, with additional N (2–60 kg N ha−1) supplied by the sorbents and compost. Crop yield was similar in all N treatments, indicating N sufficiency, with the poultry litter + biochar treatment statistically matching the yield of the no-N control. Confirming our hypothesis, mineral N fertiliser resulted in the highest concentrations of soil inorganic N, followed by poultry litter and the amended poultry formulations. Reflecting the soil inorganic N concentrations, the average N2O emission factors ranked as per the following: mineral fertiliser 8.02% > poultry litter 6.77% > poultry litter + compost 6.75% > poultry litter + bentonite 5.5% > poultry litter + biochar 3.4%. All emission factors exceeded the IPCC Tier 1 default for managed soils (1%) and the Australian Government default for sugarcane soil (1.25%). Our findings reinforce concerns that current default emissions factors underestimate N2O emissions. The laboratory incubations broadly matched the field N2O emissions, indicating that in vitro testing is a cost-effective first step to guide the blending of organic wastes in a way that ensures N sufficiency for crops but minimises N losses. We conclude that suitable sorbent-waste formulations that attenuate N release will advance N efficiency and the circular nutrient economy.

Organic matter amendments improve soil fertility in almond orchards of contrasting soil texture

The effects of organic matter amendments (OMA) on soil fertility in permanent cropping systems like orchards is under-studied compared to annual cropping systems. We evaluated experimentally the impact of OMAs on soil fertility in almond (Prunus dulcis) orchards over a two-year period with annual applications. Two OMAs, derived from composted green waste (GWC) or composted manure wood chips (MWC), were applied as surface mulch and compared to a control at two sites with different soil textures (sandy loam and loamy sand). OMAs increased soil moisture content (0–0.1 m depth) at both sites by 27–37%. Both amendments increased soil inorganic N at the sandy loam (GWC: 194%; MWC: 114%) and loamy sand (GWC: 277%; MWC: 114%) sites the month following application, but soil inorganic N concentrations quickly decreased to values similar to those of control plots. After two-years, the GWC and the MWC amendments increased the soil cation exchange capacity (CEC) by 112% and 29%, respectively, in the sandy loam site, but no change was observed in the loamy sand site. The greatest increase in soil extractable K occurred in the GWC-amended plots at the sandy loam site even though the initial K concentration of MWC was higher. Both OMAs increased soil organic carbon (SOC) after two years, but the SOC increase in the GWC-amended plots was greater. Our results suggest that OMAs can significantly improve soil fertility after one or two annual applications, and that fertility gains appear to be dependent on soil texture than the nutrient concentrations of the OMA.

Extending Cover Crop Benefits with Zone Till Management in Northern Organic Summer Squash Production

Winter annual legume cover crops often fail to reach full maturity by spring vegetable planting dates in northern climates, which prevents maximum nitrogen (N) contributions. To determine if delayed termination improved cover crop biomass and N content, we evaluated winter rye + hairy vetch (Secale cereale L. + Vicia villosa Roth) and oat + field pea (Avena sativa L. + Pisum sativum L.) cover crop mixtures in 2015 and 2016, and medium red clover (Trifolium pratense L.) in 2016, in zone-tilled organic yellow crookneck squash (Cucurbita pepo var. torticollis Harz). In-row regions where cover crops were terminated in early spring during crop row preparation were compared to between-row regions where termination was delayed until legume maturation in late spring. Soil quality (soil inorganic N, permanganate oxidizable C (POXC), and potentially mineralizable N (PMN)) was also determined for in-row and between-row regions at four time points throughout the growing season. In 2015, winter rye + hairy vetch biomass N more than doubled between early and late termination times, with 120 and 258 kg N ha−1, respectively. Permanganate oxidizable C was not responsive to cover crop systems or tillage, and only slightly decreased over time in 2016. Soil inorganic N and PMN after cover crop termination in 2016 provided evidence of localized soil N cycling responses to cover crop termination in in-row and between-row regions. The extended growing period for cover crops between crop rows in the first several weeks of crop growth had no negative effect on crop yield, and appeared to enhance soil fertility.

Seasonal patterns and related microclimatic drivers of soil inorganic nitrogen in an urban montane cloud forest

Understanding the matter and energy dynamics in environments with strong human influence is essential since it allows us to know relevant ecological drivers in urban green land areas. It has been hypothesized that biogeochemical cycles in urban forests are more open (susceptible to nutrients soil losses) with respect to rural forests near cities. However, it is not clear if this ecosystem function occurs in the same way in systems from different latitudes. Soil nutrient dynamics and microclimatic conditions of an urban and a nearby rural montane cloud forest were registered from January 2016 to July 2017. Our objective was to compare edaphic and micro-climatic factors that drive soil inorganic N dynamics in these forests. Climate was slightly cooler and drier, and soil C, N, P and organic matter were lower in the urban than the rural forest. Seasonal soil inorganic N forms were related to above ground conditions in the urban forest, but to the belowground conditions in the rural forest. Consistently low NH4:NO3 ratio indicated high susceptibility to N soil loss in the urban forest. Our results support the hypothesis that urban cloud forests are functioning as open ecosystems in contrast to the rural forests.

Rye cover crop improves vegetable crop nitrogen use efficiency and yields in a short-season growing region

Cover crops have the potential to immobilize nitrogen (N) that would otherwise be lost before or after the main crop production, leading to improved N management. However, information on how cover crops influence N management in intensive vegetable cropping systems are scarce. This study aimed to determine how an overwintering rye cover crop impacts crop yield and N cycling, for three common prairie vegetable crops. From 2017 to 2019, a broccoli-sweet corn-root crop sequence was tested (in which all crops of rotation were present each year), with each crop type receiving five N fertilizer treatments, ranging from 0 to 300 kg N ha-1. After harvest each year, sub-plots were established with vs without a rye cover crop, and the effect on vegetable yield, soil inorganic N, and N use efficiency (NUE) was followed into the subsequent growing season. In most cases, the cover crop increased vegetable crop productivity and N content in the subsequent growing season. The cover crop also lowered soil inorganic N levels at vegetable planting but increased levels at harvest. Vegetable crop NUE indices were frequently improved with vs without the cover crop. As for the N fertilizer response, increasing N fertilizer rate did not continually increase vegetable crop productivity and N content. Higher N fertilizer rates increased soil inorganic N levels at vegetable planting and harvest, and often lowered vegetable crop NUE indices. These results demonstrate the importance of adjusting soil N levels to better align with crop needs—and that including a rye cover crop in the vegetable rotation is one method of doing so.

Effect of biofuel waste, urea, deer browsing and vegetation control on Pinus banksiana seedling growth on a dry upland site in central Canada

Ash from biofuels and nitrogen fertilizer are increasingly being used as soil amendments. While this can increase tree growth, it can also increase mammalian grazing and competition with vegetation. We applied moderate amounts (1.5 t ha^-1 y^-1) of ash and 74 kg N ha^-1 y^-1 of urea in each of two years to a well-drained site in southeastern Manitoba, planted with <i>Pinus banksiana</i>. Subplots received deer browsing and/or vegetation control. The ash resulted in an increase in pH in the upper 15m of mineral soil from ca. 5.7 to 6.6, and the urea created short-term spikes in soil inorganic N (NH₄ and NO₃) levels. Urea combined with ash significantly increased seedling relative growth rates in the first two years, with seedlings being largest with urea, with or without ash. However, by the fourth year seedling growth and size did not differ between the amendments. Urea application increased browsing damage to 91 %, but only when vegetation was mowed. Browsing guards resulted in seedlings having 1.6 times greater shoot mass by the end of the fourth growing season. These results suggest that on sandy soils in the dry region of central Canada, <i>P. banksiana</i> may get little benefit from ash applications.

Long-Term Cultivation of Fruit Plantations Decreases Mineralization and Nitrification Rates in Calcareous Soil in the Karst Region in Southwestern China

Determination of rates of mineralization of organic nitrogen (N) into ammonium-N (NH4+-N) and nitrification of NH4+-N into nitrate-N (NO3−-N) could be used to evaluate inorganic N supply capacity, which, in turn, could guide N fertilizer application practices in crop cultivation systems. However, little information is available on the change of mineralization and nitrification in soils under fruit cultivation systems converted from forestlands in karst regions. In a 15N-tracing study, inorganic N supply capacity in forest soils and three typical fruit crop soils under long-term cultivation was investigated, in addition to factors influencing the supply, in calcareous soils in the karst regions in southwestern China. Long-term fruit crop cultivation decreased soil organic carbon (SOC), total N, and calcium concentrations, cation exchange capacity (CEC), water holding capacity (WHC), pH, and sand content, significantly, but increased clay content. Compared to that of forests, long-term fruit crop cultivation significantly decreased mineralization and nitrification rates to 0.61–1.34 mg N kg−1 d−1 and 1.95–5.07 mg N kg−1 d−1, respectively, from 2.85–6.49 mg N kg−1 d−1 and 8.17–15.5 mg N kg−1 d−1, respectively, but greatly increased the mean residence times of NH4+-N and NO3−-N. The results indicate that long-term fruit crop cultivation could decrease soil inorganic N supply capacity and turnover in karst regions. Both mineralization and nitrification rates were significantly and positively correlated with SOC and total N concentrations, CEC, and WHC, but negatively correlated with clay content, suggesting that decreased soil organic matter and increased clay content were responsible for the decline in mineralization and nitrification rates in soils under long-term cultivation of fruit crops. The results of the present study highlight the importance of rational organic fertilizer application in accelerating soil inorganic N supply and turnover under long-term cultivation of fruit crops in karst regions.