J. A. Díez

Nitrate leaching from soils under a maize-wheat-maize sequence, two irrigation schedules and three types of fertilisers

Abstract To implement measures to tackle the nitrate leaching problem it is necessary to assess the effect of alternative agricultural practices in vulnerable zones. A 3-year experiment was conducted at La Poveda Field Station (30 km southeast of Madrid, Spain) to assess the effects of irrigation schedules (conventional vs. efficient) and fertiliser types (unfertilised control, urea, Floranid32 (a slow-release N fertiliser), and municipal organic waste (MOW) compost) on nitrate leaching, grain yield and N uptake by plants. Treatments were combined in a factorial model and distributed to 24 plots. Chemical fertilisers were applied at the rate of 150 kg N ha−1 to maize (1993 and 1995 growing seasons) and 100 kg N ha−1 to wheat (1994 growing seasons). The MOW compost was applied at a single dose before 1993 maize planting at the rate of 27.5 Mg ha−1. Conventional irrigated plots were overwatered and the water input in efficient irrigated plots was dosed according to plant consumption. Nitrate discharge was calculated by multiplying the seasonal drainage volume by the concentration of nitrates in soil water solution, both at 1.4 m soil depth. Seasonal drainage was calculated by using the water balance equation after measuring water movement (tensiometers) and water storage throughout the soil profile (neutron probe). Nitrate concentration was measured in samples extracted with ceramic cups. Drainage losses throughout the experiment were 184 and 38 mm in plots irrigated with conventional and efficient schedules, respectively. Corresponding nitrate-nitrogen discharge in both sets of plots were 128 and 25 kg N ha−1 across fertiliser types. The nitrate discharge in unfertilised plots from the soil N reserve was on average half than that in fertilised ones. The MOW compost treatment combined with efficient irrigation showed promise in controlling nitrate discharge. Maize yields were unaffected by fertiliser type, but wheat yields decreased by 33% in unfertilised plots. It is concluded that, at a given rate of chemical fertiliser, nitrate loading to the aquifer can be traced to drainage discharge and that safe loading of MOW compost to soils requires control of water inputs.

Controlling nitrate pollution of aquifers by using different nitrogenous controlled release fertilizers in maize crop

Abstract The effects of applying different commercial, controlled release fertilizers (CRF) as a means of controlling NO 3 − pollution of groundwater in an irrigated maize crop were tested. The polluting effects of two sources of irrigation water with different NO 3 − content were also evaluated. The results showed that conventional agricultural practices are one of the main causes of NO 3 -aquifer pollution. Excess nitrogenous fertilization occurs because of the lack of soil monitoring to rationalize the fertilizer dosages and because the flood irrigation system, used with the frequency and rates applied, accelerates NO 3 − leaching. The results also show the inefficient use made of water. An analysis of the results, using the evolution of the NO 3 -leaching rate, proved to be a more reliable source of information for assessing pollution than the concentrations detected in the soil water solution, below the root zone when the water flow was downwards. The use of two different sources of irrigation water (well, 43 mg NO 3 − l −1 and stream, 3 mg NO 3 − l −1 ) showed no significant differences on the NO 3 − leached during the maize growing period owing to the high levels detected in the soil and the high dosages of N applied. In the stream irrigation water experiment, a greater polluting effect was observed with conventional fertilizer application (urea) than with CRF. The results obtained with Floranid 32 showed the effects of control over NO 3 − leaching both in the case of stream and well-water irrigation sources. With Multicote this is only observed with the use of NO 3 − free water.

Effect of the type of fertilizer and source of irrigation water on N use in a maize crop

An experiment in a maize crop evaluated the influence of several types of commercial nitrogenous fertilizers with different action mechanisms — urea (soluble), Floranid-32 (low water solubility) and Multicote 4 (coated fertilizer) — on maize grain and biomass yields, as well as on plant N use. The fertilizers were applied as a top-dressing of 294 kg N ha−1. All treatments additionally received 64 kg N ha−1 as 8.0 (N):6.5 (P):12.5 (K) compound prior to seedbed preparation. The influence of NO−3 content in the irrigation water was also assessed, using water with either 2.5 or 35 mg l−1 of NO−3. Irrigation plus rainfall totalled 513 mm (1.20 potential ET). Nitrogen lost during the cultivation period was calculated from the N balance of the topsoil. Results obtained under these experimental conditions showed that the type of fertilizer did not alter maize grain and biomass yields. Yields for maize irrigated with the higher NO−3 water were systematically greater than those obtained with irrigation water of low NO−3 content. Nitrogen lost from the topsoil during the cultivation period varied between 240 and 280 kg N ha−1 for all treatments, and was well correlated with NO−3-N leached into the aquifer during the same period.

Effect of timing of application of municipal solid waste compost on N availability for crops in central Spain

Abstract To calculate the correct nitrogen fertilizer rate for crops and the possibility of using municipal solid waste (MSW) compost as an organic amendment, nitrogen mineralization rates were studied by laboratory incubation and field measurements in a soil in central Spain. Nitrogen mineralization rates were studied in a 250-day laboratory soil incubation with two treatments: with and without compost, incubated at 28°C and a moisture content of 70% of field capacity. Three phases are described: (1) no increase in the mineral nitrogen content, (2) a linear increase in the mineral N fraction and, finally, (3) a linear, parallel increase in both mineral N and easily mineralizable organic N fractions. Incubation data were fitted to three different equations. The exponential model proposed by Stanford and Smith (1972) was selected to predict field N mineralization rates. The field experiment was performed using a crop of maize with three treatments: compost applied in February (before sowing), compost applied during sowing and a control (without compost application): sampling was carried out over 14 months. Soil water content was measured periodically. Soil with compost applied in February showed 1.9 and 1.4 times more available nitrogen than soil without compost and compost at sowing, respectively, for the month of maximum accumulation. These results suggest that compost amendments must be applied before sowing. Compost applications were shown to supply the available nitrogen for spring crops. A simulation model showed satisfactory agreement with field data, after correction for soil temperature and water content.

Nitrous oxide emission and denitrification nitrogen losses from soils treated with isobutylenediurea and urea plus dicyandiamide

Abstract. The aim of this study was to quantify the effects of two N compounds commonly used in controlled release fertiliser (CRF) and bio-inhibitor-amendment fertiliser formulations on denitrification N losses and N2O emission from several soil types at different soil moisture levels. The compounds tested were the slightly soluble isobutylenediurea (IBDU), and urea mixed with the nitrification inhibitor, dicyandiamide (DCD). Unfertilised soils and soils treated with urea alone served as controls. A significant variation in N2O emission and denitrification rates was observed between the fertiliser treatments. This variation was found to be attributable to the nature of the chemical compounds and not to changes in NH4+ or NO3– concentrations. The diminished denitrification rate over time for all the fertiliser treatments was probably associated with the decay of denitrifying microbes. N2O emission could generally be correlated with the denitrification rate and the contribution of nitrification was estimated to be low. The addition of the nitrification inhibitor DCD to the urea showed no appreciable effect on denitrification compared with urea alone but did affect N2O emission. Generally, the IBDU treatment gave rise to the greatest denitrification N loss, while losses due to N2O emission were lower than control values in many of the trials. The ratio denitrification loss:N2O emission increased with the soil moisture and clay content of each type of soil, and generally, this ratio was highest for soils treated with IBDU. The soil property that most strongly influenced denitrification and N2O emission was water-filled pore space.

Control of nitrate pollution by application of controlled release fertilizer (CRF), compost and an optimized irrigation system

A nitrogenous controlled release fertilizer (Floranid 32) and a treatment of municipal organic waste compost were tested under two irrigation managements (conventional and ET-adjusted irrigation rates) with the aim of assessing risk of nitrate leaching to the aquifer. A check without N fertilizer was introduced. The experiment was carried out at La Poveda Field Station (30 km SE Madrid, Spain) in alluvial soils with water table depth at 4 m and under maize cropping. The experiment was laid out in a randomized complete block design with three replications, allocating 12 plots to each irrigation management. Although N fertilizer rate (150 kg ha−1) was reduced at half as related to a previous experiment, no difference in grain yields was observed. This result relates to a high content of soil-N. Floranid showed promising results in controlling N-leaching in comparison with urea that exhibited an accelerated rate of N release which finally determines low use of N by the plant and marked NO3− leaching. Treatment of municipal waste compost showed NO3− concentrations in the soil water solution of similar values as those of urea at 140 cm. ET-adjusted irrigation showed no drainage during the corn growing season and lower NO3− concentrations in the soil water solution which could indicate a general lower rate of N solubilization.

Available Nitrogen for Corn and Winter Cereal in Spanish Soils Measured by Electro‐ultrafiltration, Calcium Chloride, and Incubation Methods

Abstract Comparison of methods is necessary to develop a quick and reliable test that can be used to determine soil‐available nitrogen (N) in an attempt to increase the efficiency of N fertilizers and reduce losses. The objectives of this research were to compare the fractions extracted by the calcium chloride (CaCl2) and the electro‐ultrafiltration (EUF) methods and to correlate them to the mineralization rate (k) obtained from a 112‐d incubation of 61 soil samples. Thirty‐five soil samples were collected from cornfields and 26 from winter cereal fields. Subsamples were either aerobically incubated to calculate k or extracted by the EUF and CaCl2 methods to identify three fractions: nitrate (NO3 −)‐N, ammonium (NH4 +)‐N, and Norg‐N. The Norg‐N extracted by both methods was larger in soils from cornfields than in soils from winter cereal fields. In samples from cornfields, the Norg‐N fraction obtained by the EUF method was correlated to the Norg‐N measured by the CaCl2 method (r=0.46). Soil N content was related to k in samples from cornfields (r=0.40) but not in samples from winter cereal fields. Also, k was correlated to inorganic N content extracted by both chemical methods. The CaCl2 method was a reliable alternative for laboratories to determine soil‐available N for corn but not for winter cereal.

Effect of sewage sludge on nitrogen availability in peat

SummaryWe studied the effect of incubating peat with lime and sewage sludge in small proportions on biological activity and N mineralization. The peat response was dependent on pH and, in acid peats, on mineralization capacity. In acid peats, the addition of sewage sludge inhibited biological activity. Only the most eutrophic peats (Herbosa) responded with accelerated mineralization. The addition of lime to acid peats favoured organic matter mineralization, shown by a greater CO2 release. The best results were obtained by adding lime and sewage sludge together. In saline peats, the best N levels were obtained without incubation.

Controlling phosphorus fixation in calcareous soils by using coated diammonium phosphate

In this paper, phosphorus fixation in calcareous soils is controlled by means of rosin-coated diammonium phosphate pellets, with several rates of phosphorus release. Four soils from arid regions in the Spanish south-east were chosen and separately treated with one of the following fertilizers: superphosphate (SP) or diammonium phosphate (DAP) coated with 0, 10 or 22% rosin with a dosage of 1000 Kg P/ha. After treatment, the soils were incubated for 8 months, in the course of which samples were taken to evaluate the evolution of P availability by means of the electroultrafiltration (EUF) technique.The results obtained show that the use of DAP with a 22% coating enables phosphorus fixation in calcareous soils to be controlled. The coating was sufficiently stable to last for the time it takes the crop to grow.

Comparison of Two Methods for Nitrogen Extraction of Irrigated Spanish Soils and Related Nitrogen Balance Calibrations

Abstract To establish the rate of nitrogen (N) fertilizer to be applied to a soil, the quantity of available N already present should be known, which requires that the mineralizable N content of the soil be determined. This work assesses the mineralizable N content of irrigated Mediterranean soils on the basis of the N extracted by the CaCl2 and electro-ultrafiltration (EUF) methods. Nineteen soils characteristic of central Spain were selected for this study. These mainly limestone soils had been used to cultivate maize using irrigation, and are subject to a Mediterranean-influenced continental climate. The regression equation relating the Norg obtained by the two methods−Norg(EUF I + II) = −0.580 + 0.144 Norg(CaCl2)—allows EUF-Norg to be determined from CaCl2-Norg in other soils of analogous physicochemical and climatological characteristics. To determine the N balance, a field experiment was performed with maize for two years in one of the selected soils. The N balance allows the mineralized N to be determined in the soil (of which it is an intrinsic characteristic) throughout crop growth. From these results, the Norg obtained by the two extraction methods (CaCl2 and EUF) was calibrated, which allowed the available soil N to be determined three months before sowing using the equation