Tesis doctoral de José Luis Gabriel
Cover crops in dry regions have been often limited by low nutrient and water use efficiency. This study was conducted during 4.5 years to determine the effect of replacing fallow by a cover crop on maize yield, and relevant aspects of n dynamics and soil salinity in an intensive maize production system. Treatments studied during the maize (zea mays l.) Intercrop period were: barley (hordeum vulgare l.), Vetch (vicia villosa l.), Fallow and, for some studies, rapeseed (brassica napus l.). All treatments were irrigated adjusting to crop evapotranspiration, and fertilised with 210 kg n ha-1 as ammonium nitrate splitted in two top dressing applications. A microplot was established during 3 years in each plot with double labeled ammonium nitrate. Measures of biomass and n content were obtained for maize and cover crops, determination of crop canopy parameters were based on digital image analysis, and root depth in sensor readings. Soil nmin and electrical conductivity in saturated paste extracts were obtained twice every year after each crop. Soil water content was monitored daily to a depth of 1.3 m with capacitance probes, based on responses to electromagnetic properties in soil, calibrated and validated for the experiment under field and laboratory conditions. Suction cups were installed at 1.2 m depth in each plot in order to obtain no3- and salts concentration in soil solution at that depth. Soil water content measurements were used for calibration and validation of the numerical model wave to describe the water balance. replacing fallow with cover crops did not affect subsequent maize yield significantly but affected n uptake. Vetch increased n supply by mineralization of legume residues after the second year, and the n content in grain by the third. Maize n fertilizer recovered was not affected by treatment and averaged 46%, but barley recovered more fertiliser during the autumn-winter period than vetch or fallow. N recovered from fertilizer comprised 19% in barley aerial biomass, while only 4% in vetch. The legume enhanced soil fertilizer recovery more than the other treatments, suggesting that the n was incorporated in a fairly stable organic fraction unavailable for maize uptake or lost. Replacing fallow by a cover crop only reduced fertiliser losses in a year with abundant precipitation. Nevertheless, reduction in soil nmin in vetch and fallow treatments was similar, showing that n losses could be reduced in this cropping system, either by replacing fallow with barley or by reducing n fertiliser application. nitrate leaching was calculated multiplying the soil solution nitrate concentration at 1.2 m depth by the drainage estimated with the calibrated wave model. During 3.5 years, nitrate leaching in the fallow, vetch, and barley was 346, 245, and 129 kg n-no3- ha-1, respectively; occurring more than 77% during the intercrop period. In dry winters, no3- accumulated in the topsoil, and cover crops controlled the no3- leaching during the initial maize growth stages. Vetch was less efficient than barley at controlling leaching, but enhanced soil n retention. The cover crops controlled no3- leaching and recycled n inside the cropping system. salt leaching was calculated multiplying total dissolved salts in the soil solution at 1.2 m depth by the drainage, and used to obtain a salt balance. Salt leaching in the fallow was 26 mg ha-1, whereas less than 18 in the presence of a cover crop. Periods of salt gain occurred more often in the cover crops than in the fallow. By the end of the experiment, net salt losses occurred in all treatments, owing to occasional periods of heavy rainfall. The cover crops were more prone than the fallow to reduce soil salt accumulation during the early growth stages of the subsequent cash crop. cover crop extra costs with respect to fallow were calculated. Cover crop biomass production and maize yield effect were fitted to distribution probabilities and n fertilizer saving was estimated as a function of n uptake by aerial and root cover crop biomass. Monte-carlo simulations were applied in order to obtain an uncertainly analysis of the benefits when residues were sold, left in the soil, or reduced from fertilizer application. Vetch and barley treatments increased benefits with respect to the fallow more than 50% of the years even if residue was not sold or fertilizer saving was not considered. When residue was sold, vetch treatment increased benefits 86% of the years with 509 â,¬ ha-1 on average, barley 76% with 309 â,¬ ha-1 and rapeseed 56% and 111 â,¬ ha-1. With the actual economic situation, either leaving the vetch and barley residue in the field, with fertiliser saving, or selling it as forage, increases the economic benefit with respect to the fallow. Selling the cover crop residue as animal feeding generated more economic benefits than fertilizer savings. Some advantages of cover cropping does not require residue incorporation (i.E. Reducing no3- and salt leaching), therefore, more specific studies should be conducted to decide under which conditions replacing fallow with cover crops in irrigated systems could combine economic and environmental benefits.
Datos académicos de la tesis doctoral «Evaluation of replacing fallow with cover crops in irrigated maize production systems«
- Título de la tesis: Evaluation of replacing fallow with cover crops in irrigated maize production systems
- Autor: José Luis Gabriel
- Universidad: Politécnica de Madrid
- Fecha de lectura de la tesis: 28/10/2011
Dirección y tribunal
- Director de la tesis
- badillos Quemada Saenz
- Tribunal
- Presidente del tribunal: pedro María Aparicio tejo
- ines Minguez tudela (vocal)
- dolores Quilez saez de viteri (vocal)
- jaume Lloveras vilamanyá (vocal)