Analysis of the spatial and temporal variability of irrigated maize yield.

The quantitative analysis of the yield of seven irrigated plots of land sown with maize was carried out over a period of 3 yr in order to determine the spatial and temporal variability. The methodology used was based on: inter-annual analysis of yield, which quantifies the overall difference in production from 1 yr to the next; and temporal variance, which indicates the variability of yield at a given point over time. The results show that even with irrigated crops, where production factors are generally subject to high degree of control, there is a high degree of inter-annual variability, becoming less marked over time. These results enable an investment risk map associated with a given crop and a given plot to be drawn; they also enable it to be shown that the sum of the yield for stable zones for each field decreases as field area increases, indicating that the greater the length of the centre pivot irrigator used, the lower the temporal stability of yield. The most stable yields are associated with an average distance of about 15m from the flow lines; finally, the results show that forecasting for future years is extremely difficult owing to the fact that the temporal variability of yield may vary between 1 and 8 t/ha

Relationship between Distance to Flow Accumulation Lines and Spatial Variability of Irrigated Maize Grain Yield and Moisture Content at Harvest

Analysis of yield variability factors is an important issue in order to obtain information that allows the delineation of areas with stable yield patterns for application of precision agriculture techniques. The objective of this study was to evaluate the spatial and temporal variability of yield and grain moisture content at harvest with their distance to flow accumulation lines, based on 3-yr data of centre-pivot irrigated maize crop in Southern Portugal. Yield data were collected over the period from 2002 to 2004 and divided into data sets relating to nine classes of distances to flow accumulation lines. Based on these data sets, the relation between yield and grain moisture content at harvest with distance to flow accumulation lines was analysed. Results show that there is an increase in yield with the decrease of distance to flow accumulation lines, both in years with normal or above-normal applied irrigation water. In situations where insufficient irrigation water was applied, grain moisture content at harvest shows an increase as distance to flow accumulation lines decreases, but in years in which more irrigation water was applied, less grain moisture content at harvest near the flow accumulation lines was observed

Agricultura de Precisão. Exemplo da avaliação do efeito da topografia e da rega sobre a variabilidade espacial e temporal da produtividade do milho.

Caso de estudo sobre o efeito da topografia e da rega sobre a variabilidade espacial e temporal da produtividade do milho. Pretende-se demonstrar a capacidade que a Agricultura de Precisão pode ter na redução do risco empresarial da actividade agrícola, através da apresentação de um caso concreto

Evaluation of the relationship between maize yield spatial and temporal variability and different topographic attributes

Maize yield data were collected in seven agricultural fields irrigated by centre-pivot irri-gation systems, in Southern Portugal, from 2002 to 2004. These data were then correlated with different primary and secondary topographic attributes. The attained correlation coefficients were used to evaluate the relationship between yield spatial variability and each individual topographic attribute. In this three-year period applied water was always lower than crop water requirements. The increase of applied water in 2004 resulted in an improvement in average yield and especially in yield spatial stability. Average yield showed a strong dependency on topography, with high correlation coefficients between yield and elevation and slope. It presented also a high correlation with topographic indices that reflect field water availability, such as the wetness index and distance to flow accumulation lines (DFL). The DFL index was the topographic index with higher correlation coefficients with yield. The negative coefficients of correlation between yield and DFL, attained in most fields in the three-year study period, show that, in general, yield increases with the decrease of DFL, i.e., with the increase of water availability. In undulating land areas flow lines are very abundant, which means that, in these conditions, the DFL index can be a good tool to evaluate yield spatial variability

Spatial Variability of Irrigated Corn Yield in Relation to Field topography and Soil Chemical Characteristics

Corn yield, topography and soil characteristics were sampled on a 26 ha area of a centre pivot irrigated cropland. The aim of the study was to determine relationships between corn yield, field topography and soil characteristics. The study was carried out in the Alentejo region of Portugal. Corn yield was measured with a combine harvester fitted with a grain-flow sensor and positioned by means of the Global Positioning System (GPS). A grid-based digital elevation model (DEM) with 1-m resolution was constructed and several topographic attributes were calculated from the DEM: the local slope gradient (S), profile curvature (Curv), specific catchments area (SCa), and a steady-state wetness index (W). Yield and topographical attributes were computed for areas of radius 5, 10, 25 and 50 m, being considered its maximum, minimum, range and average values. The soil was systematically sampled with a mechanical probe for a total of 109 soil profiles used for analysis of the following soil superficial (<0.30 m) characteristics: extractable phosphorous (P2O5) and extractable potassium (K2O), soil pH, cation exchange capacity (CEC) and exchangeable bases. With centre pivot irrigation systems, the Wave50 index was shown to be useful for the identification of field areas in which low corn yields may be due to lack of water. At the same time, SCa was found to be useful for the identification of field areas in which low yields are due to excess water and drainage problems. Higher positive correlation between pH, Ca and Curv were observed; calcium concentration was found on the transition areas between flat surfaces to concave ones, while lower values were detected in convex and concave areas. Topographical indexes, namely Wave50, SCa and Curv, can be especially helpful in site-specific management for delineating areas where crop yields are more sensitive to extreme water conditions

AGRICULTURA DE PRECISÃO. Exemplo da avaliação do efeito da topografia e da rega sobre a variabilidade espacial e temporal da produtividade do milho.

Este artigo não tem como objectivo definir o que é a agricultura de Precisão, nem esgotar as possíveis aplicações que esta tem na actividade agrícola. Pretende-se apenas demonstrar a capacidade que a agricultura de precisão pode ter na redução do risco empresarial da actividade agrícola, através da apresentação de um caso concreto

Description standards of primary tillage implements

Recent research has shown that different types of tillage implements have a different impact on soil translocation. Tillage experiment descriptions in the bibliography are usually incomplete in their description of the implements and the experimental tillage conditions, which makes some difference if one wants to compare different experiments through time and space. The aim of this paper is to present a diagnostic of the problem, showing the importance of describing the implements and at the same time to present a proposal for a standard description of mouldboards, disc harrows and cultivators that should be taken into account when tillage experiments are carried out

Soil carbonation processes as evidence of tillage-induced erosion

Tillage-induced soil erosion or redistribution increases spatial variation of several soil properties and often reduces the productive capacity of soil resources. Our objectives were to identify the extent of this type of erosion by observing the changes in soil morphological properties in the field and analysing its possible effects on soil productivity. The study was initiated in 2001 and conducted at two irrigated sites located approximately at Terena, Alandrol, 80 km east of Évora, Portugal. They were planted to corn (Zea mays L.) during this study, but have a long history of agricultural use with a trend toward increasing intensity in recent years. Soils in the field studies are classified mainly as Calcaric Regosols, Calcaric Cambisols, Luvisols and small areas of Fluvisols. The amount of erosion was estimated by simulation and verified by describing the lithology and measuring soil carbonates. The presence of carbonates in the superficial Ap horizons of soils that were previously devoid of this compound, provide evidence of soil redistribution: (1) in soils derived from calcareous parent material, this is the result of a re-carbonation process; (2) in soils derived from non-calcareous parent material the presence of carbonates in the superficial Ap horizons results from a carbonation process. On both sites, A and B, approximately 17% of the soils sampled were either carbonated or re-carbonated. Carbonation and re-carbonation of soil profiles confirmed that tillage had redistributed the soil-ploughing layer over time. Decreased corn yield was also observed as slope increase. If current agricultural practices are continued in this area, a decrease in soil quality and maximum yield on higher slopes can be expected

Propivot – ferramenta para avaliação do impacto da rega por rampa rotativa

A ferramenta PROPIVOT é uma aplicação informática, escrita em linguagem Avenue e optimizada para o Sistema de Informação Geográfica ArcView 3.2., que permite avaliar qualitativamente os riscos de escorrimento e de erosão de uma rampa rotativa (center-pivot), instalada ou a instalar numa determinada área. Tem como objectivo servir de apoio ao técnico que vai fazer o dimensionamento do sistema de rega, permitindo-lhe modelar o efeito da utilização de máquinas com determinadas características e em determinadas situações topográficas e de solos, avaliando qualitativamente os riscos da sua utilização nessas condições. A ferramenta apresenta como resultado final uma série de mapas da parcela em estudo com a identificação das zonas problemáticas, no que se refere ao risco de escorrimento e à erosão e perda de solo, obtidas em função dos diferentes dados de entrada do programa

Avaliação Qualitativa do Risco de Escorrimento e Erosão na Rega por Rampa Rotativa utilizando Sistemas de Informação Geográfica

Os sistemas de informação geográfica combinados com as metodologias de dimensionamento das rampas rotativas mostram potencialidades para funcionarem como uma ferramenta integrada muito útil no apoio ao técnico que vai fazer o dimensionamento da máquina. A aplicação PROPIVOT permite modelar o efeito da utilização de uma rampa rotativa, com determinadas características hidráulicas, num terreno com uma dada topografia e tipo de solos, permitindo avaliar qualitativamente os riscos de escorrimento e erosão do solo devidos à sua utilização nessas condições, as zonas da área regada que apresentam maiores problemas e escolher uma máquina cujas características de funcionamento possam minimizar o escorrimento e a erosão. Em situações de sistemas já instalados a identificação de zonas problemáticas poderá ajudar o agricultor a alterar a gestão da rega utilizada, ou definir melhor o modo de utilização da terra optando por sistemas de produção com técnicas de não mobilização ou mobilização reduzida do solo que minimizem os riscos de escorrimento e erosão