N-only Treatments Research Articles

The amounts and ratio of nitrogen and phosphorus addition drive the rate of litter decomposition in a subtropical forest

Nitrogen (N) and phosphorus (P) control biogeochemical cycling in terrestrial ecosystems. However, N and P addition effects on litter decomposition, especially biological pathways in subtropical forests, remain unclear. Here, a two-year field litterbag experiment was employed in a subtropical forest in southwestern China to examine N and P addition effects on litter biological decomposition with nine treatments: low and high N- and P-only addition (LN, HN, LP, and HP), NP coaddition (LNLP, LNHP, HNLP, and HNHP), and a control (CK). The results showed that the decomposition coefficient (k) was higher in NP coaddition treatments (P < 0.05), and lower in N- and P-only addition treatments than in CK (P < 0.05). The highest k was observed with LNLP (P < 0.05). The N- and P-only addition treatments decreased the losses of litter mass, lignin, cellulose, and condensed tannins, litter microbial biomass carbon (MBC), litter cellulase, and soil pH (P < 0.05). The NP coaddition treatments increased the losses of litter mass, lignin, and cellulose, MBC concentration, litter invertase, urease, cellulase, and catalase activities, soil arthropod diversity (S) in litterbags, and soil pH (P < 0.05). Litter acid phosphatase activity and N:P ratio were lower in N-only addition treatments but higher in P-only addition and NP coaddition treatments than in CK (P < 0.05). Structural equation model showed that litter MBC, S, cellulase, acid phosphatase, and polyphenol oxidase contributed to the loss of litter mass (P < 0.05). The litter N:P ratio was negatively logarithmically correlated with mass loss (P < 0.01). In conclusion, the negative effect of N addition on litter decomposition was reversed when P was added by increasing decomposed litter soil arthropod diversity, MBC concentration, and invertase and cellulase activities. Finally, the results highlighted the important role of the N:P ratio in litter decomposition.

Combining N fertilization with biochar affects root-shoot growth, rhizosphere soil properties and bacterial communities under sugarcane monocropping

High-dose nitrogen (N) fertilization has been widely adopted to achieve higher yield in intensive sugarcane monocropping system in Southern China, while long-term excessive N fertilization causes high N losses and negative environmental impacts. Biochar (BC) has been considered a soil amendment to potentially improve soil fertility and crop productivity. However, little is known about the effects of N fertilization combined with BC on sugarcane growth, rhizosphere soil characteristics and microbial community composition. In this study, a greenhouse-pot experiment with six treatments in triplicates was carried out to examine the responses of root-shoot growth, rhizosphere soil properties and bacterial communities to different BC and N fertilization treatments in sugarcane monocropping soil (duration over 20 years). The results demonstrated that N fertilization combined with BC promoted the aboveground growth of sugarcane, while different dose of BC exhibited a significant effect on switching root and shoot growth responses. With the increase in the BC amendment rate, the rhizosphere soil pH, TC and C/N ratio increased correspondingly. As compared with the N-only treatment, N fertilization combined with moderate dose of BC significantly decreased soil NO3--N and nitrification potential (SNP), whereas N treatment with higher-dose BC resulted in a sharp increase in SNP. DESeq2 analysis revealed that N fertilization coupled with higher BC-amendment enriched Mesorhizobium, Porphyrobacter, Rhizobacter and Allorhizobium-Neorhizobium-Pararhizobium-Rhizobium. Redundancy analysis indicated that soil pH, NO3--N and C/N were key edaphic factors that shifted the soil bacterial community composition, especially for nitrifying flora and N-fixing flora. The above findings suggest that the combination of N fertilization with moderate-dose BC might be an alternative strategy to promote crop growth and soil sustainability under sugarcane monocropping system.

Simultaneous effects of biochar and nitrogen fertilization on nitrous oxide and methane emissions from paddy rice

Synthetic fertilizers are major agents of gaseous emissions including nitrous oxide (N2O), and rice cultivation is a primary source of methane (CH4) emission. Biochar (BC) addition to agricultural soils is a potential approach to mitigate N2O and CH4 emissions. This greenhouse study was conducted to assess the simultaneous effects of BC and nitrogen (N) fertilization to reduce N2O and CH4 emissions along with higher biomass accumulation in rice under controlled conditions. Nine treatment combinations of BC amendments at 0, 2 and 4% by weight (weight of BC/weight of soil) mixed into 3500 g of unsterile soil with 0, 70 and 140 kg N ha−1 were used in growing rice. Results show that BC-only treatments enhanced the volumetric water contents (VWC) by 9–14% and soil pH by 5–7% coupled with higher daily and cumulative seasonal CH4–C fluxes by 85–95% and 48–51%, respectively, compared with control treatment. Under 2% and 4% BC amendments, N at 140 kg ha−1 lowered the daily and cumulative seasonal CH4–C fluxes by 24–42% and 20–30%, respectively as compared to 70 kg N ha−1. Furthermore, BC amendments in N-treated soils reduced the daily and total seasonal N2O–N emissions by 27–67% and 49–61%, respectively, relative to N-only treatments. However, N addition in BC-amended soils showed 10–16% decreased VWC compared with the BC-only treated soils. In terms of rice growth, BC-only reduced the above- and below-ground biomass accumulation, delayed the tillering phase, and resulted in fewer vegetative tillers except for BC-treated pots with 140 kg N ha−1. Thus, this study suggests that the use of BC amendment at 2% with 140 kg N ha−1 may be a beneficial strategy to reduce the net GHG emissions from paddy rice in an Alfisol.

Deep soil carbon after 44 years of tillage and fertilizer management in southern Illinois compared to forest and restored prairie soils

No-till (NT) management can reduce soil erosion and increase soil carbon (C) in agricultural systems, but there is less certainty regarding deeper soil and how long-term tillage and fertilization practices compare to other land-use systems. The objective of this study was to quantify tillage and fertilizer management effects after 44 years (20 years in continuous corn [Zea mays L.] and 24 years in corn–soybean [Glycine max L.] rotation) on bulk density and soil C concentrations and stocks to a 1 m (3.3 ft) depth in a somewhat poorly drained Bethalto silt loam near Belleville, Illinois, and compare to nearby forest and restored prairie soils. Four tillage (moldboard plow, chisel tillage [ChT], alternate tillage, and NT) and five fertilizer (no fertilization control, nitrogen [N]-only, N + N-phosphorus-potassium [NPK] starter, NPK + NPKstarter, and NPK broadcast) treatments showed bulk density was lower in NT than moldboard plow treatments in 0 to 15 (0 to 6 in) and 25 to 50 cm (10 to 20 in) depths. Complete NPK treatments generally resulted in higher C stocks than N-only and control treatments from 0 to 25 cm (0 to 10 in), but no differences were detected from 25 to 100 cm (10 to 39 in) or 0 to 100 cm (0 to 39 in) due to fertilizer. No-till management increased C stocks compared to tillage treatments for 0 to 15 cm (0 to 6 in) and was greater than the ChT treatment for 0 to 100 cm (0 to 39 in). No-till/NPK maintained greater cumulative soil C stocks to 1 m than either undisturbed forest soils or restored prairie soils. Additionally, NT/NPK had the maximum soil C increase over time of 0.36 Mg C ha−1 y−1 (0.16 tn C ac−1 yr−1) for the top 15 cm (6 in) over 44 years.

Understanding planktonic vs. benthic algal response to manipulation of nutrients and light in a eutrophic lake

ABSTRACTSteinman A, Abdimalik M, Ogdahl ME, Oudsema M. 2016. Understanding planktonic vs. benthic algal response to manipulation of nutrients and light in a eutrophic lake. Lake Reserve Manage. 32:402–409.We examined the environmental factors influencing the growth of benthic and planktonic algae in Lake Macatawa, a hypereutrophic lake located in west Michigan. Turbidity may limit planktonic growth in the main body of the lake, despite high P concentrations, whereas shallow water depths in the littoral regions of the lake may allow benthic algal growth. We experimentally amended nutrients to benthic algae using nutrient diffusing substrates near the sediment surface and to phytoplankton using nitrogen (N) and phosphorus (P) spikes into 10 L carboys suspended from a PVC-constructed frame near the water surface to test how nutrient and light regimes influence these potentially competing autotrophic communities. Benthic algae were co-limited by N and P, whereas phytoplankton were P-limited. The N-only treatments resulted in negative algal growth. In addition, microcystin concentration (phytoplankton only) also responded positively to P additions and negatively to N-only treatments. We speculate that much of the P in this lake is bound to sediment and not bioavailable, so despite the high total P concentrations, the algae are P-limited at certain times of the year. Irradiance levels did not seem to be photosynthetically limiting during this study. Our results have management implications: (1) use of TP as an indicator of P limitation may be flawed without concomitant measurement of bioavailable P; and (2) control of external P loading is critical to directly limit phytoplankton abundance but also can result in indirect control of benthic algae if internal P loading from the sediment is a key source of P to this community.

Nitrous Oxide Emission and Denitrifier Abundance in Two Agricultural Soils Amended with Crop Residues and Urea in the North China Plain.

The application of crop residues combined with Nitrogen (N) fertilizer has been broadly adopted in China. Crop residue amendments can provide readily available C and N, as well as other nutrients to agricultural soils, but also intensify the N fixation, further affecting N2O emissions. N2O pulses are obviously driven by rainfall, irrigation and fertilization. Fertilization before rainfall or followed by flooding irrigation is a general management practice for a wheat-maize rotation in the North China Plain. Yet, little is known on the impacts of crop residues combined with N fertilizer application on N2O emission under high soil moisture content. A laboratory incubation experiment was conducted to investigate the effects of two crop residue amendments (maize and wheat), individually or in combination with N fertilizer, on N2O emissions and denitrifier abundance in two main agricultural soils (one is an alluvial soil, pH 8.55, belongs to Ochri-Aquic Cambosols, OAC, the other is a lime concretion black soil, pH 6.61, belongs to Hapli-Aquic Vertosols, HAV) under 80% WFPS (the water filled pore space) in the North China Plain. Each type soil contains seven treatments: a control with no N fertilizer application (CK, N0), 200 kg N ha-1 (N200), 250 kg N ha-1 (N250), maize residue plus N200 (MN200), maize residue plus N250 (MN250), wheat residue plus N200 (WN200) and wheat residue plus N250 (WN250). Results showed that, in the HAV soil, MN250 and WN250 increased the cumulative N2O emissions by 60% and 30% compared with N250 treatment, respectively, but MN200 and WN200 decreased the cumulative N2O emissions by 20% and 50% compared with N200. In the OAC soil, compared with N200 or N250, WN200 and WN250 increased the cumulative N2O emission by 40%-50%, but MN200 and MN250 decreased the cumulative N2O emission by 10%-20%. Compared with CK, addition of crop residue or N fertilizer resulted in significant increases in N2O emissions in both soils. The cumulative N2O emissions from the treatments of 250 kg N ha-1 were 1.1–3.3 times higher than those of treatments with 200 kg N ha-1 in both soils with adding equal amounts of the same type of crop residue. Abundance of the 16S rRNA gene did not significantly change in all treatments in two soils, but the nosZ and nirS genes were more abundant in soils amended with crop residues compared with CK or N-only treatments. N2O emission, however, were not related to the abundance of denitrifier containing nirS or nosZ. The research provided some information regarding the effect of crop residues with N fertilizer on N2O emissions and denitrifier abundances in two soils. Our results imply the property of crop residue and rate of N fertilizer are important influencing factors of N2O emission when crop residues combined with N fertilizer are applied to different agricultural soils.

Digestate from Biogas Plants is an Attractive Alternative to Mineral Fertilisation of Kohlrabi

This study examined the potential for the use of digestate from biogas plants for the fertilisation of kohlrabi. Kohlrabi was grown in two pot experiments in consecutive years using digestate, mineral fertiliser (urea) with a nitrogen (N) content equivalent to that in the digestate, mineral fertiliser with N, phosphate (P), potassium (K) and magnesium (Mg) contents equivalent to the digestate, and an unfertilised control. At harvest, the soil receiving the digestate application had higher P, K and Mg contents than the control and the urea treatment. The soil Nmin content was balanced in all fertilised treatments. Soil pH was unaffected by all treatments. Kohlrabi bulbs from the unfertilised control had the lowest weight, nitrate content and ascorbic acid content. Digestate and NPKMg fertiliser treatments increased bulb weight compared with the N-only urea treatment. Ascorbic acid content did not differ between fertilised treatments. There were no differences in bulb nitrate content between the mineral fertiliser treatments, but digestate application gave a low nitrate content. Bulb macroelement contents varied irregularly among treatments.

Vegetation feedbacks of nutrient addition lead to a weaker carbon sink in an ombrotrophic bog

To study vegetation feedbacks of nutrient addition on carbon sequestration capacity, we investigated vegetation and ecosystem CO2 exchange at Mer Bleue Bog, Canada in plots that had been fertilized with nitrogen (N) or with N plus phosphorus (P) and potassium (K) for 7-12 years. Gross photosynthesis, ecosystem respiration, and net CO2 exchange were measured weekly during May-September 2011 using climate-controlled chambers. A substrate-induced respiration technique was used to determine the functional ability of the microbial community. The highest N and NPK additions were associated with 40% less net CO2 uptake than the control. In the NPK additions, a diminished C sink potential was due to a 20-30% increase in ecosystem respiration, while gross photosynthesis rates did not change as greater vascular plant biomass compensated for the decrease in Sphagnum mosses. In the highest N-only treatment, small reductions in gross photosynthesis and no change in ecosystem respiration led to the reduced C sink. Substrate-induced microbial respiration was significantly higher in all levels of NPK additions compared with control. The temperature sensitivity of respiration in the plots was lower with increasing cumulative N load, suggesting more labile sources of respired CO2 . The weaker C sink potential could be explained by changes in nutrient availability, higher woody : foliar ratio, moss loss, and enhanced decomposition. Stronger responses to NPK fertilization than to N-only fertilization for both shrub biomass production and decomposition suggest that the bog ecosystem is N-P/K colimited rather than N-limited. Negative effects of further N-only deposition were indicated by delayed spring CO2 uptake. In contrast to forests, increased wood formation and surface litter accumulation in bogs seem to reduce the C sink potential owing to the loss of peat-forming Sphagnum.

Effect of nutrient loading on biogeochemical and microbial processes in a New England salt marsh

Coastal marshes represent an important transitional zone between uplands and estuaries. One important function of marshes is to assimilate nutrient inputs from uplands, thus providing a buffer for anthropogenic nutrient loads. We examined the effects of nitrogen (N) and phosphorus (P) fertilization on biogeochemical and microbial processes during the summer growing season in a Spartina patens (Aiton (Muhl.)) marsh in the Narragansett Bay National Estuarine Research Reserve on Prudence Island (RI). Quadruplicate 1 m2 plots were fertilized with N and P additions, N-only, P-only, or no additions. N-only addition significantly stimulated bacterial production and increased pore water NH 4 + and NO 3 − concentrations. Denitrification rates ranged from 0 to 8 mmol m−2 day−1. Fertilization had no apparent effect on soil oxygen consumption or denitrification measured in the summer in intact cores due to high core-to-core variation. P fertilization led to increased pore water dissolved inorganic phosphorus (DIP) concentrations and increased DIP release from soils. In contrast the control and N-only treatments had significant DIP uptake across the soil-water interface. The results suggest that in the summer fertilization has no apparent effect on denitrification rates, stimulates bacterial productivity, enhances pore water nutrient concentrations and alters some nutrient fluxes across the marsh surface.

Post-establishment fertilization of Minnesota hybrid poplar plantations

Experimental plantings were installed at five sites in three locations in western Minnesota. Aboveground biomass production increased 43–82% as a result of three annual applications of urea or balanced nutrient blend fertilizer beginning near canopy closure. There were no production differences between the type of fertilizer used, indicating that N was the major limiting nutrient. Responses were consistent from site to site, indicating that hybrid poplar stands in this region at this stage of development would be very responsive to fertilization. Leaf tissue N, P, and K concentrations increased in response to both fertilizer treatments; P and K increased more frequently in response to the blend treatment compared to the N-only urea treatment. The diagnosis and recommendation integrated system (DRIS) indices indicated that the stands were near optimal nutritional balance prior to fertilization. Treatments increased individual leaf area and leaf litter production up to 33% and 37%, respectively. Canopy leaf area, leaf N concentration and the sum of DRIS indices were correlated with aboveground production. Growth efficiency, the ratio of production to canopy leaf area, increased with both fertilizer treatment and successive years of treatment, indicating improved stand vigor due to nutrient amendments. Stand production increased more in response to changes in leaf N concentration as stands aged. Plantation production continued to increase with increased internal N concentration even when deficiency levels or levels defined as sufficient for fast growth were exceeded. The correlation between aboveground production and the sum of DRIS indices shows that optimal nutrition at canopy closure may result in current aboveground dry matter production exceeding 13 Mg ha � 1 yr � 1 . Multiple small-dose amendments appear to be effective in increasing production by

Effects of different sources and rates of sulphur on the growth and foliar nutrition of nitrogen-fertilized lodgepole pine

The effects of nitrogen (N) fertilizer, alone and in combination with different sources and rates of sulphur (S), on foliar nutrients and tree growth are reported over 3 and 6 years, respectively. After 3 years, foliar S levels in the N+S treatments were significantly higher than those in N-only treatments at all six study locations. Temporal patterns of foliar S response varied significantly with S source. When applied as ammonium sulphate (AS), foliar levels increased sharply in year 1 and slowly declined over the next 2 years. Conversely, additions of elemental S (S0), in the form of S0 – sodium bentonite fertilizer, usually did not increase foliar S concentration in year 1, but had increasingly positive effects on foliar S in years 2 and 3. An increase in the S application rate from 50 to 100 kg/ha resulted in only a modest improvement in foliar S concentration for both S sources. Differences in individual-tree basal area increment between N and N+S treatments were statistically significant in only two of six trials. Prefertilization levels of foliar N and sulphate S, and probable induced deficiencies of nonadded nutrients following N fertilization, largely explained basal area and height responses to N and N+S additions at the six study sites. Despite delayed oxidation, S0 was as effective as the more readily available AS in stimulating radial growth after 6 years. However, the relative effectiveness of S source varied with S application rate in two trials. In both cases, basal area increment was positively related to application rate when S was applied as AS. Conversely, the effect of application rate was distinctly negative when S0 was applied. Despite large differences in short-term availability of AS and S0, the results from this study support the conclusion that the two S sources are likely equally effective in alleviating S deficiencies and in promoting tree growth of S-deficient lodgepole pine (Pinus contorta Dougl. var. latifolia Engelm.).

262 FERTIGATION VERSUS DRY APPLICATION OF NITROGEN AND PHOSPHORUS FERTILIZER IN IRRIGATED `GALA' AND `FUJI' APPLES

Differential fertilizer application method (single dry, split dry, fertigated liquid), irrigation method (drip, microjet), and nutrient source (N vs. N+P in year 2+) were established in Spring 1992 in a newly planted Gala and Fuji apple orchard. In Spring 1993, the drip-fertigated Gala trees had 3 times and the drip-fertigated Fuji trees had 8 times more flower clusters per tree than the other treatments Fruiting was not allowed in 1993. Trunk cross-sectional area (TCSA) in Fall 1992 was not influenced by treatments. By Fall 1993, TCSA was still independent of treatment for the Fuji trees; however, the Gala trees fell into two size groups - (larger) microsprinkler-fertigated and split dry broadcast; and (smaller) drip fertigated and single-time spring dry broadcast. TCSA had increased 284% (Fuji) and 265% (Gala) since planting. None of the treatment effects were substantially influenced by fertigating with N+P vs N only. Leaf concentrations of most nutrients were consistently lower in 1993 than in 1992. Leaf Fe was higher in 1993 because the orchard was dustier. Leaf N was lower in the microsprinkler-fertigated trees than in all other treatments. Fertigation with N+P did not consistently produce higher leaf P than the N-only treatments. Leaf Mn varied with treatment: microsprinkler fertigated &lt; drip fertigated, single dry &lt; split dry. Treatment effects on all other elements were inconsistent (K, Ca, Mg, B, Cu) or absent (Zn, Fe).

Microbial biomass P, labile P, and acid phosphatase activity in the humus layer of a spruce forest, after repeated additions of fertilizers

A 20-year-old forest fertilization trial was used to investigate the effects of repeated P additions on P availability in the humus layer of a Norway spruce forest soil. N was supplied annually, and P, K, and micronutrients were supplied every 4th year. The last P application was made 2 years before the investigation started. Microbial P concentrations in the P+NK+micro-amended plots were about half as high as those in the control and the N-only treatment. In plots without P amendments, around 50% of the total P in the humus layer was found in microorganisms, whereas in P-amended plots the figure was around 25%. The block supporting more rapid tree growth, situated on the middle of a slope, showed a significantly higher microbial biomass P concentration than the less productive block at the bottom of the slope. Labile P concentrations did not vary between treatments and thus could not have directly contributed to the treatment-related differences in total microbial biomass P. Acid phosphatase activities were around three times lower in the sites treated with P+NK+micro-nutrients. Two sources are suggested for the acid phosphatases, active excretion by living roots and fungi and passive release from ruptured cells. For all eight plots investigated, there was a positive correlation (R=0.83) between acid phosphatase activity and the microbial P concentration. The P concentration in current-year needles was the lowest in the N-only treatment at 1,13 mg g-1 dry weight, and the highest in the P+NK + micronutrients + lime treatment at 1.92 mg g-1 dry weight. The P:N ratio in needles varied from 0.115 in the P+NK + micronutrients + lime plots to 0.068 in the N-only plots. The latter value is at the level where P is considered to be the growth rate-determining nutrient.