Burning and cultivation effects on greenhouse gas emissions and nutrients in wetland soils from Saskatchewan,Canada

Wetland fringe areas in prairie agricultural landscapes may be subjected to burning of vegetation in autumn followed by cultivation in spring. The objective of this study was to examine the greenhouse gas (CO₂, N₂O and CH₄) emissions and plant nutrient (NO₃, PO₄ and SO₄) supplies in wetland fringe soils as affected by simulated burning + cultivation, at field capacity and saturation moisture content. Using undisturbed soil cores collected from grassed wetland fringes at four sites in southern Saskatchewan, the impacts were examined over a 20-day period. The burning + cultivation treatment generally reduced CO₂ emissions, tended to increase NO₃–N availability, and had no consistent effect on N₂O emissions, or PO₄–P and SO₄–S supply. Production of CH₄ occurred only at one site, and only under saturated conditions. Compared to field capacity, saturation reduced CO₂ emissions and NO₃–N supply, tended to increase PO₄–P availability, and had no consistent effect on N₂O emissions and SO₄–S. The CO₂ emissions and SO₄–S were greater for soil cores with higher organic matter and salinity, respectively. The N₂O emissions were only occasionally related to soil NO₃–N supply rate.     

Squash yield, nutrient content and soil fertility parameters in response to methods of fertilizer application and rates of nitrogen fertigation

Two field experiments were conducted to evaluate squash yield and nutrient content in response to different fertigation nitrogen (N) rates and method of fertilizer N application. The following treatments were studied in a randomized complete block design with four replications: zero N (N0), 50 (N1), 100 (N2) and 150 (N3) mg l^–3 N concentration in the irrigation water (IW) (fertigation treatments) and a soil application treatment (NS) equivalent to the N2 treatment. Irrigation was applied to replenish 80% of the Class A pan evaporation twice a week. Compared to the control (N0), shoot dry matter and yield were increased by all fertigation N rates and by the soil application treatment. However, soil application gave a lower yield than the equivalent fertigation N rate, indicating the comparative advantage of fertigation. The lowest fertigation N rate was adequate to give the highest yield in the first season, while in the second season a higher rate was necessary to achieve the maximum yield. The growth and fruit yield were higher in the second season as a result of the more favorable climatic conditions. Regression relationships indicate that the yield and the shoot dry weight were related to the fertigation N rates by polynomial quadratic relationships. The response to N in the second season was greater, as indicated by the steeper positive slope. The fruit yield was linearly related to both fruit number and fruit size in both seasons. N contents in shoots increased with N addition and were higher in both fruit and shoot during fruiting with the fertigation method. Soil salinity slightly increased with N application, especially in the top 15 cm, but remained low and acceptable for normal plant growth. Soil P increased mainly in the top soil following phosphoric acid application to all plots. Restricted P movement to deeper soil is attributed to the expected precipitation and/or sorption reactions with Ca and Mg in calcareous soils. It can be concluded that fertigation is more effective than soil application in increasing the yield and with fertigation lower N rates would be adequate to produce higher yield, thus lowering fertilization cost and minimizing environmental impact of over-fertilization.     

Contribution of nitrification and denitrification to N2O production in peat, clay and loamy sand soils under different soil moisture conditions

Agricultural soils are a significant source of nitrous oxide (N₂O). Since mitigation of greenhouse gas emissions is needed in all sectors of society, it is important to identify the processes producing N₂O and the factors affecting the production rates in agricultural soils. This study aimed to elucidate the N₂O production in peat, clay and loamy sand at four different soil moisture conditions (40, 60, 80 and 100% Water Filled Pore Space). The ace­tylene inhibition technique was used to evaluate the contribution of nitrification to N₂O production. Nitrous oxide production responded markedly to soil moisture in all three soils. The highest N₂O production, measured at the wettest soils (100% WFPS), was up to four orders of magnitude higher than that at the dry soils (40% WFPS). In dry conditions N₂O production decreased in the order of peat > clay > loamy sand, while in wet conditions the highest N₂O production was measured in loamy sand, then in peat, and the lowest in clay soils. Nitrification was the dominant N₂O producing process in all the soils at 60% WFPS. In the sandy soil 70% of the total N₂O production originated from nitrification, while in the peat soil most of the total N₂O production originated from denitrification. Data on processes producing N₂O in agricultural soils are needed to develop process-based models that could reduce the uncertainty of the emission estimates in greenhouse gas inventories.     

Soil organic carbon,total nitrogen and grain yields under long-term fertilizations in the upland red soil of southern China

A long-term experiment with various fertilizations was carried out during 1990–2006 in a double cropping system rotated with wheat (Triticum Aestivium L.) and corn (Zea mays L.) in the red soil of southern China. The experiment consisted of eight treatments: non-fertilization (CK), nitrogen–phosphorus fertilization (NP), phosphorus–potassium fertilization (PK), nitrogen–phosphorus–potassium fertilization (NPK), pig manure (M), pig manure and NPK fertilization (NPKM), high rates of NPKM (hNPKM), and straw returned with inorganic fertilizers (NPKS). Applications of manure (i.e., M, NPKM and hNPKM) significantly increased soil organic carbon (SOC) and total nitrogen contents. Applications of inorganic fertilizers without manure showed small influences on SOC, but resulted in declines of soil total nitrogen over the long-term experiment. Grain yields were more than doubled under fertilizations for both wheat and corn, with the highest under the NPKM and hNPKM treatments and the lowest under non-fertilization. Long-term cropping practices without fertilization or with unbalanced fertilizations (e.g., NP and PK) caused low grain yields. The balanced fertilization of NPK increased grain yields. However, such practice was not able to maintain high grain yields during the last few years of experiment. Our analyses indicate that both wheat and corn grain yields are significantly correlated with SOC, total and available nitrogen and phosphorus. However, the relationships are stronger with total nitrogen (r = 0.5–0.6) than with available nitrogen (r = 0.26–0.3), indicating the importance of maintaining soil total nitrogen in agricultural practice.