José Luis Gabriel

The kill date as a management tool for cover cropping success.

Integrating cover crops (CC) in rotations provides multiple ecological services, but it must be ensured that management does not increase pre-emptive competition with the subsequent crop. This experiment was conducted to study the effect of kill date on: (i) CC growth and N content; (ii) the chemical composition of residues; (iii) soil inorganic N and potentially mineralizable N; and (iv) soil water content. Treatments were fallow and a CC mixture of barley (Hordeum vulgare L.) and vetch (Vicia sativa L.) sown in October and killed on two different dates in spring. Above-ground biomass and chemical composition of CC were determined at harvest, and ground cover was monitored based on digital image analysis. Soil mineral N was determined before sowing and after killing the CC, and potentially mineralizable N was measured by aerobic incubation at the end of the experiment. Soil water content was monitored daily to a depth of 1.1 m using capacitance sensors. Under the present conditions of high N availability, delaying kill date increased barley above-ground biomass and N uptake from deep soil layers; little differences were observed in vetch. Postponing kill date increased the C/N ratio and the fiber content of plant residues. Ground cover reached >80% by the first kill date (∼1250°C days). Kill date was a means to control soil inorganic N by balancing the N retained in the residue and soil, and showed promise for mitigating N losses. The early kill date decreased the risk of water and N pre-emptive competition by reducing soil depletion, preserving rain harvested between kill dates and allowing more time for N release in spring. The soil potentially mineralizable N was enhanced by the CC and kill date delay. Therefore kill date is a crucial management variable for maximizing the CC benefits in agricultural systems.

Quantitative characterization of five cover crop species

SUMMARY The introduction of cover crops in the intercrop period may provide a broad range of ecosystem services derived from the multiple functions they can perform, such as erosion control, recycling of nutrients or forage source. However,the achievementof these services in a particularagrosystemisnot always requiredat the same time or to thesamedegree.Thus,species selection anddefinitionof targeted objectivesiscritical whengrowing covercrops. The goal of the current work was to describe the traits that determine the suitability of five species (barley, rye, triticale, mustard and vetch) for cover cropping. A field trial was established during two seasons (October to April) in Madrid (central Spain). Ground cover and biomass were monitored at regular intervals during each growing season. A Gompertz model characterized ground cover until the decay observed after frosts, while biomass was fitted to Gompertz, logistic and linear-exponential equations. At the end of the experiment, carbon (C), nitrogen (N), and fibre (neutral detergent, acid and lignin) contents, and the N fixed by the legume were determined. The grasses reached the highest ground cover (83–99%) and biomass (1226–1928 g/m 2 ) at the end of the experiment. With the highest C:N ratio (27–39) and dietary fibre (527–600 mg/g) and the lowest residue quality (*680 mg/g), grasses were suitable for erosion control, catch crop and fodder. The vetch presented the lowest N uptake (2·4 and 0·7 g N/m 2 ) due to N fixation (9·8 and 1·6 g N/m 2 ) and low biomass accumulation. The mustard presented high N uptake in the warm year and could act as a catch crop, but low fodder capability in both years. The thermal time before reaching 30% ground cover was a good indicator of early coverage species. Variable quantification allowed finding variability among the species and provided information for further decisions involving cover crop selection and management.

Data supporting the cover crops benefits related to soil functionality in a 10-year cropping system

In this data article we provide different field parameters of an agricultural irrigated system under Mediterranean conditions. These parameters represent the response of variables related to soil functionality to different cover crops. Soil and plant samples were taken from fallow and cover crops treatments over the course of 10 years, with most variables measured every other year. This ample database provides reliable information to design sustainable agricultural practices under Mediterranean conditions. Researchers, policy makers and farmers are interested in the final outcome of this dataset. The data are associated with the research article entitled “Cover crops to mitigate soil degradation and enhance soil functionality in irrigated land” (García-González et al., 2018) [1].

Assessing cover crop management under actual and climate change conditions

The termination date is recognized as a key management factor to enhance cover crops for multiple benefits and to avoid competition with the following cash crop. However, the optimum date depends on annual meteorological conditions, and climate variability induces uncertainty in a decision that needs to be taken every year. One of the most important cover crop benefits is reducing nitrate leaching, a major concern for irrigated agricultural systems and highly affected by the termination date. This study aimed to determine the effects of cover crops and their termination date on the water and N balances of an irrigated Mediterranean agroecosystem under present and future climate conditions. For that purpose, two field experiments were used for inverse calibration and validation of the WAVE model (Water and Agrochemicals in the soil and Vadose Environment), based on continuous soil water content data, soil nitrogen content and crop measurements. The calibrated and validated model was subsequently used in advanced scenario analysis under present and climate change conditions. Under present conditions, a late termination date increased cover crop biomass and subsequently soil water and N depletion. Hence, preemptive competition risk with the main crop was enhanced, but a reduction of nitrate leaching also occurred. The hypothetical planting date of the following cash crop was also an important tool to reduce preemptive competition. Under climate change conditions, the simulations showed that the termination date will be even more important to reduce preemptive competition and nitrate leaching.

Water Management for Enhancing Crop Nutrient Use Efficiency and Reducing Losses

Strategies that enhance water and nutrient use efficiency in vegetable production may contribute to increase productivity and reduce diffuse (non-point source) nutrient pollution. A combination of optimal water management and applying fertilizer rates adjusted to crop requirements should not only reduce the risk of adverse environmental impact but also be the most profitable choice for the farmer. This chapter covers water management strategies oriented towards improving nutrient use efficiency in horticultural systems. Water management affects the mineralization process and the subsequent use of released nutrients, and is crucial in Mediterranean and semi-arid climates. This is particularly relevant when transforming rain fed cropping systems into irrigated ones, because the soil may increase mineralization and supply large amounts of nutrients during the transition period. Nitrogen losses occur mainly by leaching and, together with phosphorus, by erosion and runoff from open fields. Nitrate leaching is frequently the most important loss process in horticulture because large input of N fertilizer are applied to maintain high productivity, roots of many vegetable crops are superficial, and the N remaining in the field as crop residues after harvest is a large fraction of the plant N uptake. Losses by leaching and effluents from greenhouses may also be responsible for diffuse pollution. Water management greatly affects greenhouse gas emission and may help to design horticultural systems with low emissions of atmospheric pollutants. Water is also used for salinity control and irrigation can be used to mitigate some of the adverse effect of salinity on plant nutrition and growth. Therefore, an integrated fertilization program oriented towards reducing nutrient losses and maintaining farm profitability should rely on both, a rational fertilization and an efficient water management.