The influence of rainfall and tillage on wheat yield parameters and weed population in monoculture versus rotation systems.

Extreme climate events (ECEs) of drought are becoming common in Mediterranean areas and farmers need adapt agricultural practices to achieve sustainability. This field study took place in to gain insight into the effects of seasonal rainfall, tillage and crop systems on wheat yield and weed parameters. Conventional (CT), minimum (MT) and no-tillage (NT) systems in wheat monoculture and rotation cropping systems were tested during 3 years of study (2014-2015, 2015-2016 and 2016-2017). Growing Season Rainfall (GSR) was the most influential factor on yield parameters and weed population. In 2016-2017, categorized as an extreme climate event by drought, the GSR accounted for 43.4% of the historical average. This year, the wheat yield (373 kg ha-1) and harvest index (0.18) were the lowest. In 2015-2016, scarcer autumn rainfall (44 mm) affected the weed germination period, reducing the density (17 plants m-2) and diversity of weed species (3 species m-2) while yield was favoured by high winter and spring rainfall (247 mm). Our study revealed that tillage effects was not significant on wheat yield, but NT systems consistently showed higher weed density and diversity than CT and MT despite the irregular GSR during this study. The rotation system presented higher values of wheat grain yield (781 kg/ha) and dry straw biomass (1803 kg/ha) but also weed biomass (48.54 g m-2) compared to monoculture (27.50 g m-2). NT and rotation combined increased the weed community although did not reduce the wheat yield compare to conventional systems even with an ECE of drought.

N2O and CH4 emissions from a fallow-wheat rotation with low N input in conservation and conventional tillage under a Mediterranean agroecosystem.

Conservation agriculture that includes no tillage (NT) or minimum tillage (MT) and crop rotation is an effective practice to increase soil organic matter in Mediterranean semiarid agrosystems. But the impact of these agricultural practices on greenhouse gases (GHGs), such as nitrous oxide (N2O) and methane (CH4), is variable depending mainly on soil structure and short/long-term tillage. The main objective of this study was to assess the long-term effect of three tillage systems (NT, MT and conventional tillage (CT)) and land-covers (fallow/wheat) on the emissions of N2O and CH4 in a low N input agricultural system during one year. This was achieved by measuring crop yields, soil mineral N and dissolved organic C contents, and fluxes of N2O and CH4. Total cumulative N2O emissions were not significantly different (P>0.05) among the tillage systems or between fallow and wheat. The only difference was produced in spring, when N2O emissions were significantly higher (P<0.05) in fallow than in wheat subplots, and NT reduced N2O emissions (P<0.05) compared with MT and CT. Taking into account the water filled pore space (WFPS), both nitrification and denitrification could have occurred during the experimental period. Denitrification capacity in March was similar in all tillage systems, in spite of the higher DOC content maintained in the topsoil of NT. This could be due to the similar denitrifier densities, targeted by nirK copy numbers at that time. Cumulative CH4 fluxes resulted in small net uptake for all treatments, and no significant differences were found among tillage systems or between fallow and wheat land-covers. These results suggest that under a coarse-textured soil in low N agricultural systems, the impact of tillage on GHG is very low and that the fallow cycle within a crop rotation is not a useful strategy to reduce GHG emissions.

Revegetation of abandoned agricultural land amended with biosolids.

This paper reports the effects of applying 0 and 40 Mg ha(-1) of biosolids (composted sewage sludge) on the revegetation of abandoned cropland in central Spain. The experimental vegetation consisted of four wild leguminous species: Colutea arborescens, Dorycnium pentaphyllum, Medicago strasseri and Retama sphaerocarpa. The survival and growth of these shrubs were evaluated over 24 months after planting, as was the production of biomass by the spontaneous herbaceous vegetation. Application of the biosolids increased shrub growth, although it was also associated with a slight reduction in shrub survival. The spontaneous vegetation became quickly established in the amended plots; its biomass production was significantly greater than in the control plots.