Klaus Reichardt

Management effects on nitrogen recovery in a sugarcane crop grown in Brazil

The present studys objectives were to quantify the fertilizer-N and residue-N balances of a sugar cane crop under two trash management systems. The fate of nitrogen (N) derived from fertilizer (NdfF) and N derived from residue (NdfR) was studied comparing: (i) the traditional harvest system with trash burning before harvest (“trash burning”) and (ii) an alternative system without trash burning, in which crop residues are left on the soil surface (“trash mulching”). The experiment consisted of three treatments: (i) T1: at planting, the sugarcane crop was fertilized with 63 kg N ha−1 as 15N-labeled ammonium sulfate, and after the 1st harvest received unlabeled trash from T2; (ii) T2: at planting, the crop was fertilized with 63 kg N ha−1 as unlabeled ammonium sulfate. At the 1st harvest time, this treatment received the labeled trash from T1; (iii) T3: at planting, the crop was fertilized with 63 kg N ha−1 as 15N-labeled ammonium sulfate, and every year, immediately before cutting, the crop residues were burnt. After the first harvest fertilizer-N was applied over the total soil area at a rate of 80 kg N ha−1 as unlabeled ammonium sulfate. The results indicated that the trash remaining as a surface blanket resulted in an average N recycling of 105.0 kg ha−1 year−1, while the practice of burning the trash produced an average N loss from the system of 83.5 kg ha−1 year−1. At the first harvest, about 75% of the labeled N was recovered in the soil–plant system. The majority was found in the plant, indicating a high availability of the fertilizer-N for the crop. At the end of the third crop cycle (2nd ratoon crop harvest), the total output of fertilizer-N (export+burning) was 60% for the burnt-trash treatment, and only 42% (export) for the trash-blanket treatment. The N liberated from the residue is mainly immobilized in the soil, reflecting that sugarcane trash is an N source of slow availability to the crop. This study indicated that green cane harvesting followed by mulching leads to a more efficient recycling of the N applied to the system and therefore reducing fertilizer-N needs.

Software to model soil water retention curves (SWRC, version 2.00)

A software for the adjustment of soil water retention curves (SWRC) is presented, using twelve models found in the literature.

Soil water content temporal-spatial variability of the surface layer of a Loess Plateau hillside in China

Surface soil moisture exhibits an important variability in terms of spatial and temporal domains, which may result in critical uncertainties for agricultural water management. The purposes of this study were (i) to characterize the temporal dynamics and stability of the spatial variability of the surface 0-6 cm soil water content theta on a hill-slope; (ii) to investigate issues related to soil moisture conditions including dominating factors on Soil Moisture and to the estimation of the mean theta. During a period of more than one month theta was measured on thirteen days by Frequency Domain Reflectometry using a 10 x 10 m grid of measurement points covering a 60 x 280 m domain within a hill-slope of the Loess Plateau in China. Soil water content exhibited a moderate variability for each measurement date, and the correlation length (lambda) for theta ranged from 8.4 to 27.7 m. With the soil becoming drier, lambda decreased, the CV% and the sampling number for accurate mean 0 estimation increased. Aspect, elevation, organic matter content, clay content, and bulk density were the main influencing factors, whose extent of influence weakened with decreasing theta. Based on time stability analysis and on the correlation of mean relative difference of theta with the relative difference of dominating factors, mean theta values were well estimated, with a better accuracy under wetter conditions.

Variability of soil water content and bulk density in a sugarcane field

The change in management practices of the sugarcane crop in Brazil, from the traditional trash burning before harvest to the new practice that leaves harvest residues on the field after harvest, can lead to alterations in the water regime and also in soil compaction levels. In this study a neutron-gamma surface gauge was used to monitor spatial and temporal variabilities of soil moisture and density in a experimental sugarcane area submitted to 3 harvest management practices: (i) mulched crop with harvest residues, (ii) crop with bare inter-row, and (iii) crop with ash residues from trash burning before harvest. Variability of soil water content and bulk density was studied using geostatistical tools and analysis of variance was used to compare averages. Autocorrelations and semivariograms indicate a spatial dependence of soil water contents, which were higher in the presence of trash residues left on the soil surface after harvest. The average difference between treatments (i) and (ii) was about of 15%, indicating the beneficial mulching effect with respect to soil water retention. Differences between (ii) and (iii) were much smaller.

STATE-SPACE APPROACH FOR THE ANALYSIS OF SOIL WATER CONTENT AND TEMPERATURE IN A SUGARCANE CROP

The state-space approach is used to describe surface soil water content and temperature behaviour, in a field experiment in which sugarcane is submitted to different management practices. The treatments consisted of harvest trash mulching, bare soil, and burned trash, all three in a ratoon crop, after first cane harvest. One transect of 84 points was sampled, meter by meter, covering all treatments and borders. The state-space approach is described in detail and the results show that soil water contents measured along the transect could successfully be estimated from water content and temperature observations made at the first neighbour.

Field spatial and temporal patterns of soil water content and bulk density changes

Umidade (q) e densidade do solo (rs) influenciam importantes processos no solo e planta tais como: movimento de agua, compactacao do solo, aeracao do solo e desenvolvimento radicular. Baseado neste fato, questoes referentes a variabilidade espacial e temporal de q e rs para diferentes periodos do ano e diferentes fases de desenvolvimento da cultura do cafe tornam-se de extremo interesse. Este trabalho teve como objetivo caracterizar padroes espaciais e temporais de q e rs durante diferentes periodos do ano e verificar se existem mudancas temporais significativas de rs na superficie do solo quando submetida a ciclos de umedecimento/secagem. O experimento foi conduzido em campo cultivado com cafe em um solo classificado como Nitossolo Vermelho Eutrofico. O experimento iniciou-se em maio de 2001 com espacamento de 1,75 m entre linhas e 0,75 m entre plantas. Medidas de q e rs foram feitas metro a metro ao longo de 200 m usando uma sonda de superficie neutron/gama. Durante o periodo umido nao houve padroes de diferenca espacial para q, enquanto que para o periodo seco o contrario foi observado. Estes padroes podem ser associados a eventos de precipitacao alterando a estrutura de correlacao espacial para observacoes adjacentes de q. Para rs existem mudancas temporais na superficie do solo ao longo do periodo estudado como uma consequencia dos ciclos de umedecimento/secagem no campo.

Principles of crop modeling and simulation: I. uses of mathematical models in agricultural science

A tecnica de modelagem em agricultura pode ser util para definir as prioridades de pesquisa, bem como para melhor entender as interacoes que ocorrem no sistema solo-planta-atmosfera. O modelo pode ser utilizado para estimar a importância e o efeito de certos parâmetros no intuito de definir os fatores a serem considerados. O modelador deve definir seus objetivos antes de iniciar o trabalho experimental, bem como desenvolver um modelo que atenda o objetivo proposto.

Soil bulk density evaluation by conventional and nuclear methods

Among the methods used to measure soil bulk density, the following have been prominent: paraffin sealed clod (PS), volumetric ring (VR), and the modern methods like gamma ray computed tomography (GCT) and the neutron/gamma surface gauge (SG). The objective of this work was to compare soil bulk density values obtained through these methods, with the aim of assisting researchers on the choice of the more appropriate method. For this, a 200-m spatial transect was chosen in an experimental area cultivated with coffee, belonging to ESALQ/USP, Piracicaba, SP, Brazil. The SG readings were first taken in the field and thereafter soil samples were collected at 8 different points, spaced at 25 m, for the other methods. The lowest values of soil bulk density were obtained for the SG method (average 1.468 g/cm3) and the highest for the PS (average 1.685 g/cm3), which was similar to the GCT method (average 1.684 g/cm3). The average soil bulk density for the VR method, which has been used in soil science as a standard method, was 1.544 g/cm3. The Tukey test indicates that the PS and GCT methods do not differ significantly (P > 0.05). They do differ in comparison with VR and SG, which also do not differ among themselves.

Using a computed tomography miniscanner for studying tillage induced soil compaction

Abstract Gamma-ray computed tomography (CT) is used to study thin compacted soil layers, such as millimeter thick “blades” that occur at plowing depth. The technique has the advantage, over the traditional gamma-ray attenuation techniques, of opening the possibility of measuring water contents and bulk-densities of odd-shaped samples. Being a 2-or 3-dimensional technique it is possible to detect small change of bulk-density and soil water content within the sample, even in thin layers of the order of millimeters. Results are reported for thin compacted layers in soil samples collected at the plowing depth from sugar-cane fields in Brazil, which clearly demonstrate the usefulness of this new method for compaction investigations and its quantitative evaluation.

Evaluation of a 15N plot design for estimating plant recovery of fertilizer nitrogen applied to sugar cane

Two experiments were conducted on commercial sugar cane fields cropped with the variety SP70-1143, with the objective of evaluating a single row microplot design to determine plant recovery of 15N fertilizer nitrogen. One of them used 15N-aqua ammonia and 15N-urea applied to two linear meter microplots of a ratoon crop (four replicates). The second used one linear meter microplots (three replicates) which received 15N-aqua ammonia only. The fertilizers were applied on 15cm deep furrows, located 25cm from both sides of the cane row. One linear meter of ratoon cane, inside and outside of the microplot, and on the same and adjacent rows were harvested twelve months after fertilization. The results indicate the feasibility of using single row segments of ratoon cane with 15N-fertilizer. The main advantage of this microplot design, when compared to the classical 3 contiguous row segments, is that only one third of the labeled fertilizer is needed. In a single row, in order to separate the nitrogen taken up by plants from the fertilizer applied to the row (Nrdffr), from that applied to adjacent rows (Nrdffr+1, and Nrdffr-1), the following should be considered: (a) a border segment of 0.5 to 1.0m inside the plot, so that Ndff results from plants harvested in the center of the microplot represent the actual value of fertilizer nitrogen taken up from that applied to the same row, and (b) harvest of plants from adjacent rows at equivalent positions to those sampled inside the microplot, to quantify the 15N-fertilizer uptake by outside plants (Nr+1dffr and Nr-1dffr), which is assumed to be the same as non labeled fertilizer applied to adjacent rows (Nrdffr+l and Nrdffr-1) taken up by inside plants. The Ndfftotal values should be calculated by the equation: Ndfftotal = Nrdffr + Nr+1dffr + Nr-1dffr.Com o objetivo de avaliar um modelo de parcela, na determinacao do aproveitamento pela cana-de-acucar de fertilizantes nitrogenados-15N, foram conduzidos dois experimentos em areas comerciais plantadas com a variedade SP 70-1143. Num experimento foram aplicados os adubos aquamonia-15N e ureia-15N, em parcelas constituidas de segmentos simples de linha de soqueira de cana, com 2 metros lineares de comprimento (4 repeticoes). No segundo, parcelas de l metro linear (3 repeticoes) receberam aquamonia-15N. Os fertilizantes foram aplicados em sulcos com 15cm de profundidade, abertos a 25cm de distância nos dois lados da linha de cana. Foram realizadas colheitas de l metro linear de cana no interior e fora das parcelas, na mesma linha e nas adjacentes a elas. Os resultados isotopicos evidenciaram ser perfeitamente possivel a utilizacao dessas parcelas com fertilizante-15N. A principal vantagem do modelo, comparado as parcelas convencionais com 3 segmentos contiguos, e a reducao a um terco, da quantidade de fertilizantes-15N necessaria. Na determinacao do nitrogenio absorvido pelas plantas do fertilizante aplicado na linha com adubo-15N (Nrdffr), e daquele absorvido do fertilizante nao marcado com o isotopo, aplicado nas linhas adjacentes (Nrdffr+1 e Nrdffr-1), deve-se considerar para as parcelas em questao: (a) bordadura interna de 0,5 a 1m de comprimento, para que os valores de Ndff de plantas colhidas no centro delas, representem o valor maximo do nitrogenio absorvido do fertilizante aplicado na linha; e (b) colheita de plantas nas linhas imediatamente adjacentes, em posicoes equivalentes a efetuada no interior das parcelas, a fim de quantificar o N absorvido do fertilizante-15N (Nr+1dffr e Nr-1dffr), que representa o valor do N absorvido do adubo aplicado nas linhas adjacentes, por plantas da parcela (Nrdffr+I e Nrdffr.,). O valor de Ndff^ e calculado pela equacao: Ndfftotal= Nrdffr + Nr+1dffr + Nr-1dff,.