Denitrification Rate and Its Potential to Predict Biogenic N2O Field Emissions in a Mediterranean Maize-Cropped Soil in Southern Italy

The denitrification rate in C2H2-amended intact soil cores and soil N2O fluxes in closed static chambers were monitored in a Mediterranean irrigated maize-cropped field. The measurements were carried out during: (i) a standard fertilization management (SFM) activity and (ii) a manipulation experimental (ME) test on the effects of increased and reduced application rates of urea at the late fertilization. In the course of the SFM, the irrigations following early and late nitrogen fertilization led to pulses of denitrification rates (up to 1300 μg N2O-N m−2 h−1) and N2O fluxes (up to 320 μg N2O-N m−2 h−1), thanks to the combined action of high soil temperatures and not limiting nitrates and water filled pore space (WFPS). During the ME, high soil nitrates were noted in all the treatments in the first one month after the late fertilization, which promoted marked N-losses by microbial denitrification (from 500 to 1800 μg N2O-N m−2 h−1) every time the soil WFPS was not limiting. At similar maize yield responses to fertilizer treatments, this result suggested no competition for N between plant roots and soil microbial community and indicated a probable surplus of nitrogen fertilizer input at the investigated farm. Correlation and regression analyses (CRA) on the whole set of data showed significant relations between both the denitrification rates and the N2O fluxes with three soil physical-chemical parameters: nitrate concentration, WFPS and temperature. Specifically, the response functions of denitrification rate to soil nitrates, WFPS and temperature could be satisfactorily modelled according to simple Michaelis-Menten kinetic, exponential and linear functions, respectively. Furthermore, the CRA demonstrated a significant exponential relationship between N2O fluxes and denitrification and simple empirical functions to predict N2O emissions from the denitrification rate appeared more fitting (higher concordance correlation coefficient) than the predictive empirical algorithm based on soil nitrates, WFPS and temperature. In this regard, the empirically established relationships between the denitrification rate on intact soil cores under field conditions and the soil variables provided local-specific threshold values and coefficients which may effectively work to calibrate and adapt existing N2O process-based simulation models to the local pedo-climatic conditions.

Managing soil nitrate with cover crops and buffer strips in Sicilian vineyards

When soil nitrate levels are low, plants suffer nitrogen (N) deficiency but when the levels are excessive, soil nitrates can pollute surface and subsurface waters. Strategies to reduce the nitrate pollution are necessary to reach a sustainable use of resources such as soil, water and plant. Buffer strips and cover crops can contribute to the management of soil nitrates, but little is known of their effectiveness in semiarid vineyards plantations. The research was carried out in the south coast of Sicily (Italy) to evaluate nitrate trends in a vineyard managed both conventionally and using two different cover crops (Triticum durum and Vicia sativa cover crop). A 10 m-wide buffer strip was seeded with Lolium perenne at the bottom of the vineyard. Soil nitrate was measured monthly and nitrate movement was monitored by application of a 15N tracer to a narrow strip between the bottom of vineyard and the buffer and non-buffer strips. Lolium perenne biomass yield in the buffer strips and its isotopic nitrogen content were monitored. Vicia sativa cover crop management contributed with an excess of nitrogen, and the soil management determined the nitrogen content at the buffer areas. A 6 m buffer strip reduced the nitrate by 42% with and by 46% with a 9 m buffer strip. Thanks to catch crops, farmers can manage the N content and its distribution into the soil over the year, can reduced fertilizer wastage and reduce N pollution of surface and groundwater.

Nutrition index and soil nitrate residues in grazed pastures fertilised with mineral fertiliser, pig slurry or cattle compost

A code of good practice was established by each European member state according to the nitrate directive. In Belgium, the nitrogen (N) inputs in pastures from slurry or compost are limited to 210 kg N/ha. Larger quantities can be applied when additional measurements, including soil nitrates analyses are carried on by the farmer. This trial aims to measure nitrogen balance, nitrogen nutrition index (NNI) and soil nitrates contents in pastures fertilised with mineral nitrogen fertiliser, pig slurry or cattle compost, the pastures being grazed by dairy cows and the fertilisation being brought at similar efficient N levels. NNI was calculated as the ratio of the actual N concentration to the sward N concentration it would have to be at a similar biomass in order to sustain a non limiting growth and a biomass accumulation (Lemaire and Gastal, 1997). Cattle compost was produced from cattle manure unloaded through the beaters of a spreader.

Some effects of crop rotation on the productivity of crops on a red earth in a semi-arid tropical climate

SUMMARYThe yield of crops in the low rainfall areas of eastern Kenya has been shown to vary within each season according to the crops grown in preceding seasons. This phenomenon of crop sequence was associated more especially with the amount of soil nitrates remaining at all depths in the soil than with the amount of water that may be left. The quantity of nitrates left by a crop was generally related to its vegetative bulk, its rooting habit and duration on the ground, and increased as the crops were ranked in the order: local maize, short-term maize, silage maize, beans and fallow. The beneficial effect of a bean crop or a fallow was reflected in a third crop when the intermediate crop had a low nitrogen requirement.The persistence of the relative differences in the nitrate levels in the soil would seem to be due to their low mobility under leaching.The increase in yield of a crop was shown to be due to the more rapid development of the crop when nitrate supplies were more plentiful. When the duration of the rains was short the earlier, more abundant flowering resulting from the rapid growth gave better grain set, and hence greater and more reliable yields. When crops matured in dry weather the availability of soil nitrates at depths of up to 4 ft had a positive influence on yield.Although rainfall was the main determinant of yield within each season, the use of fallowing to store water from one season to the next was inefficient. Similar amounts could be held in cropped land if late rains occurred. If early rains were plentiful the benefit of stored water could be lost by the thorough wetting of the soil profile.