Laser rangefinder-based measuring of crop biomass under field conditions

Knowledge of site-specific crop parameters such as plant height, coverage and biomass density is important for optimising crop management and harvesting processes. Sensors for measuring crop parameters are essential pre-requisites to gather this information. In recent years, laser rangefinder sensors have been adopted in many industrial applications. In agricultural engineering, the potential of laser rangefinders for measuring crop parameters has been little exploited. This paper reports the design and the performance of a measuring system based on a triangulation and a time-of-flight laser rangefinder for estimating crop biomass density in representative crops under field conditions. It was shown that the mean height of reflection point is a suitable parameter for non-contact indirect measurement of crop biomass by laser rangefinder sensors. The main parameters for potential assessment were the coefficient of determination (R ² ) and the standard error (RMSE) for the relation between crop biomass density and the mean height of the reflection point in crop stands from oilseed rape, winter rye, winter wheat and grassland during the vegetation period in 2006. For the triangulation sensor, R ² was in the range from 0.87 to 0.98 and for the time-of-flight sensor in the range from 0.75 to 0.99 for both fresh matter and dry matter density. The triangulation sensor had a reduced suitability caused by masking effects of the reflected beam and because of limited measuring range. Based on the results of experiments and technical data, it was concluded that the time-of-flight principle has good potential for site-specific crop management.     

Within-field nitrogen response in corn related to aerial photograph color

Precise management of nitrogen (N) using canopy color in aerial imagery of corn (Zea mays L.) has been proposed as a strategy on which to base the rate of N fertilizer. The objective of this study was to evaluate the relationship between canopy color and yield response to N at the field scale. Six N response trials were conducted in 2000 and 2001 in fields with alluvial, claypan and deep loess soil types. Aerial images were taken with a 35-mm slide film from ≥1100 m at the mid- and late-vegetative corn growth stages and processed to extract green and red digital values. Color values of the control N (0 kg N ha⁻¹) and sufficient N (280 kg N ha⁻¹ applied at planting) treatments were used to calculate the relative ratio of unfertilized to fertilized and relative difference color values. Other N fertilizer treatments included side-dressed applications in increments of 56 kg N ha⁻¹. The economic optimal N rate was weakly related (R ² ≤ 0.34) or not related to the color indices at both growth stages. For many sites, delta yield (the increase in yield between control N and sufficient N treatments) was related to the color indices (R ² ≤ 0.67) at the late vegetative growth stage; the best relationship was with green relative difference. The results indicate the potential for color indices from aerial photographs to be used for predicting delta yield from which a site-specific N rate could be determined.     

Spectral and thermal sensing for nitrogen and water status in rainfed and irrigated wheat environments

Variable-rate technologies and site-specific crop nutrient management require real-time spatial information about the potential for response to in-season crop management interventions. Thermal and spectral properties of canopies can provide relevant information for non-destructive measurement of crop water and nitrogen stresses. In previous studies, foliage temperature was successfully estimated from canopy-scale (mixed foliage and soil) temperatures and the multispectral Canopy Chlorophyll Content Index (CCCI) was effective in measuring canopy-scale N status in rainfed wheat (Triticum aestivum L.) systems in Horsham, Victoria, Australia. In the present study, results showed that under irrigated wheat systems in Maricopa, Arizona, USA, the theoretical derivation of foliage temperature unmixing produced relationships similar to those in Horsham. Derivation of the CCCI led to an r ² relationship with chlorophyll a of 0.53 after Zadoks stage 43. This was later than the relationship (r ² = 0.68) developed for Horsham after Zadoks stage 33 but early enough to be used for potential mid-season N fertilizer recommendations. Additionally, ground-based hyperspectral data estimated plant N (g kg⁻¹) in Horsham with an r ² = 0.86 but was confounded by water supply and N interactions. By combining canopy thermal and spectral properties, varying water and N status can potentially be identified eventually permitting targeted N applications to those parts of a field where N can be used most efficiently by the crop.     

Calibration of a capacitance probe for measurement and mapping of dry matter yield in Mediterranean pastures

The main objective of this study was to calibrate a commercial capacitance probe for measuring pasture dry matter yields under Mediterranean conditions. The standard method of assessing pasture biomass is based on cutting all the forage within a specified area and requires great effort and expense to collect enough samples to accurately represent a pasture. The field tests were carried out in 2007, 2008 and 2009 on different dates (phenological stages), and on five dairy farms, representing typical pastures in the region (grasses; legumes; and bio-diverse flora, mixture of grasses, legumes and others species). The linear regression techniques used in 2007 to relate the weight of the herbage (direct measurements) to the meter reading of capacitance (indirect measurements) led to high regression coefficients in grasses (R² = 0.90; P < 0.01) and heterogeneous botanical composition (R² = 0.87; P < 0.001) and moderate regression coefficient in legumes species (R² = 0.48; P < 0.05). The validation of the calibration equations in 2008 and 2009 in two sites showed RSME values of 130 kg ha⁻¹ in heterogeneous botanical composition and 456 kg ha⁻¹ in legumes. The results indicated that the capacitance probe together with a GPS receiver might support site-specific management of pastures which would be useful in large areas.     

Quantifying spatial variability of indigenous nitrogen supply for precision nitrogen management in small scale farming

Understanding spatial variability of indigenous nitrogen (N) supply (INS) is important to the implementation of precision N management (PNM) strategies in small scale agricultural fields of the North China Plain (NCP). This study was conducted to determine: (1) field-to-field and within-field variability in INS; (2) the potential savings in N fertilizers using PNM technologies; and (3) winter wheat (Triticum aestivum L.) N status variability at the Feekes 6 stage and the potential of using a chlorophyll meter (CM) and a GreenSeeker active crop canopy sensor for estimating in-season N requirements. Seven farmer’s fields in Quzhou County of Hebei Province were selected for this study, but no fertilizers were applied to these fields. The results indicated that INS varied significantly both within individual fields and across different fields, ranging from 33.4 to 268.4 kg ha⁻¹, with an average of 142.6 kg ha⁻¹ and a CV of 34%. The spatial dependence of INS, however, was not strong. Site-specific optimum N rates varied from 0 to 355 kg ha⁻¹ across the seven fields, with an average of 173 kg ha⁻¹ and a CV of 46%. Field-specific N management could save an average of 128 kg N ha⁻¹ compared to typical farmer practices. Both CM and GreenSeeker sensor readings were significantly related to crop N status and demand across different farmer’s fields, showing a good potential for in-season site-specific N management in small scale farming systems. More studies are needed to further evaluate these sensing technology-based PNM strategies in additional farmer fields in the NCP.     

Performance of an Ultrasonic Tree Volume Measurement System in Commercial Citrus Groves

Florida growers have planted citrus groves at varying spacings to improve resource efficiency and to optimize fruit production for maximum economic return. Four commercial groves with different row spacings and tree ages were scanned with a Durand-Wayland ultrasonic system to measure and map tree volumes and to examine the effect of row spacings and tree ages on ultrasonic measurements. The ultrasonically measured volumes (UVs) were compared with manually measured tree volumes (MVs) of 30 trees in each grove to examine the performance of the ultrasonic system. The ultrasonic system measured tree volumes reliably in different groves with an average prediction accuracy (APA) >90%, and correlation with manual measurement of R²=0.95–0.99. Standard error of prediction and root mean square errors were relatively higher in widely spaced old groves than closely spaced young groves. The ultrasonically sensed tree volume map showed substantial variation in canopy volumes (0–240 m³ tree⁻¹) within the grove. Therefore, the use of ultrasonic systems is a better option to quantify and map each tree volume rapidly (real-time) for planning site-specific management practices accurately in commercial groves and for estimating fruit yield.     

Distinguishing nitrogen deficiency and fungal infection of winter wheat by laser-induced fluorescence

One of the most important tasks in precision farming is the site-specific application of fertilisers and pesticides in heterogeneous large-area fields. For such site-specific crop management, effective remote sensing methods for the detection of crop diseases and nutrient deficiencies are required. The aim of the present work was to compare laser-induced fluorescence (LIF) parameters from nitrogen-deficient and pathogen (rust and mildew)-infected winter wheat (Triticum aestivum L.) plants and to assess the potential of LIF to detect and discriminate between these types of stress. Both long term nitrogen deficiency and pathogen infection resulted in an increase of the ratio of fluorescence at 686 and 740 nm (F686/F740) accompanied by a reduction of leaf chlorophyll content to approximately 35 μg cm⁻². A linear negative correlation between chlorophyll content and F686/F740 ratio (r² = 0.78) was found for leaves with chlorophyll content ranging between 17 and 52 μg cm⁻². Since chlorophyll breakdown appeared an unspecific symptom to both nitrogen deficiency and pathogen infection, it was not possible to discriminate between these types of stress only by means of the F686/F740 ratio. Specific for the pathogen-infected leaves was a large heterogeneity in the records of their spectral parameters caused by inhomogeneous, discrete lesions of fungi infection. Nitrogen-deficient plants with homogeneous reduction in chlorophyll content showed, in contrast, more uniform readings of the spectral parameters. Thus, mildew- and rust-infected plants, grown under sufficient nitrogen fertilisation could be distinguished from those grown under reduced nitrogen supply by the higher variance of their spectral readings. The simultaneous scanning multipoint mode measurements of LIF and laser light reflection characteristics with parallel estimation of their heterogeneity is proposed for the discrimination between nitrogen deficiency and pathogen infection under field conditions.     

Effects of nitrogen fertilizer rates and ratios of base and topdressing on wheat yield, soil nitrate content and nitrogen balance

Application of nitrogen (N) fertilizer is one of the most important measures that increases grain yield and improves grain quality in winter wheat (Triticum aestivum L.) production. Presently, there is a large number of investigations (experiments) in the field on different nitrogen fertilizer application regimes. However, there still exists a serious problem of low nitrogen use efficiency, especially in winter wheat high yield conditions: unsuitable nitrogen fertilizer, which often leads to lower yield and large accumulation of nitrate in the soil, bringing a potential risk to the environment. In order to explore the optimal regime of nitrogen fertilizer application suitable for environment and economy, a field experiment on the different rate and ratio of base and topdressing of nitrogen fertilizer at the different growth periods of winter wheat was conducted. The field experiment was undertaken from the fall of 2003 to the summer of 2004 in the village of Zhongcun in Longkou city, in the Shandong Province of China. The field experiment with three repeats for each treatment was designed in a split-plot. The major plot was applied with urea at a nitrogen fertilizer rate of three levels, namely, 0 kg·hm⁻² (CK), 168 kg·hm⁻² (A), and 240 kg·hm⁻² (B). In the sub-plot, the ratios of base and topdressing nitrogen fertilizer at the different development periods of wheat were 1/2:1/2 (A1 and B1), 1/3:2/3 (A2 and B2) and 0:1 (A3 and B3). Treatment B1 was under a regime used now in the local region. It was found that the amount of N accumulation in plants had no significant difference between treatments applied with nitrogen fertilizer. The grain yield and grain protein content were all elevated remarkably by applying nitrogen fertilizer compared with those of treatment CK. There was no significant difference in the grain yield and grain protein content between A2 and B2 and B3. However, when compared with those of B2 and B3, in A2 there was an increase in nitrogen use efficiency and residual soil NO₃ ⁻-N and N losses were reduced. Under the condition of the same rate of nitrogen fertilizer, increasing topdressing nitrogen rate clearly elevated the grain yield, grain protein content and nitrogen use efficiency. The results indicated that the residual soil NO₃ ⁻-N in A1 and B1 accumulated higher than that of CK in 80–160 cm soil layers at the jointing stage, but that of A2 had no significant difference compared with that of CK in 0–200 cm soil layers. At the maturity stage, more residual soil NO₃ ⁻-N was detected in B2, B3 and A3 than that in CK in 120–180 cm soil layers, which could not be absorbed by the roots of wheat, but led to be eluviated easily. The amount of soil NO₃ ⁻-N accumulation in treatment A2 had no significant difference compared with that of treatment CK in the 100–200 cm soil layer. In conclusion, A2, whose nitrogen fertilizer rate was 168 kg·hm⁻² and the ratio of base and topdressing was 1/3:2/3, had a higher grain yield and grain protein content, and heightened N use efficiency and minimized the risk of NO₃ ⁻-N leaching. This should be one of the most appropriate nitrogen fertilizer application regimes in wheat production in local regions in China. __________ Translated from Acta Ecologica Sinica, 2006, 26(11): 3661–3669 [译自: 生态学报]     

Effects of plastic-film mulching and nitrogen application on forage-oriented maize in the agriculture-animal husbandry ecotone in North China

To counter the actual problems of forage shortage and low quality existing in the agriculture-animal husbandry ecotone in North China, a research was conducted to study the effects of plastic-film mulching and nitrogen application on the production of forageoriented maize with the aim of producing water-saving forage with high-yield and good quality. Field experiments combined with laboratory experimental estimation and analysis was adopted. Plastic-film mulching increased the dry biomass of forage-oriented maize by 23.8% with effectively improving the maize’s nitrogen absorption so that the apparent utilization ratio and output-input ratio of nitrogen were enhanced. The content of crude protein in maize plant was increased and thus, forage nutritive quality was improved. Plastic-film mulching remodeled the maize field water consumption scheduling pattern and increased the water use efficiency by over 10%. Nitrogen application to forage-oriented maize co-improved the biomass and the nutritive quality with the nutritive matter (percentage and yield) several times of the biomass. Nitrogen application increased maize biomass production by 36.1%–39.5% and it increased the contents of crude protein and crude fat in maize plant by 109% and 145%, respectively. The yields of the two nutritive matters increased by 160% and 210%. Nitrogen application at the rate of about 200 kg·hm⁻² to the uncovered field and the rate less than 300 kg·hm⁻² to the field with film mulching were considered as the most proper rates to guarantee high yield and good quality of forage-oriented maize and were the rates to keep the available nitrogen balanced in the soil. Plastic-film mulching and nitrogen fertilizer application to forage-oriented maize was an effective way of producing forage with high yield and good quality, relieving the shortage of animal forage and accelerating ecological recovery and economic development in this ecotone in North China. __________ Translated from Scientia Agricultura Sinica, 2006, 40(6): 1206–1213 [译自: 中国农业科学]     

Neural network modeling of greenhouse tomato yield, growth and water use from automated crop monitoring data

The recent development of tools to automatically monitor important crop attributes in situ such as yield, growth and water use offers an opportunity to relate real-time crop status to current environmental conditions. In this study, continuous minute-by-minute measurements of crop yield, growth and water use averaged over weekly, daily, or hourly intervals throughout the growing season were used to determine crop response to changes in the greenhouse environment. The data were obtained from crop monitoring stations established in both commercial and research greenhouses. Crop yield measurements obtained from the monitoring system were generally in very close agreement with yields recorded over a much larger area in the commercial greenhouse. Yield was more closely related (R² = 0.65) to radiation from the previous week than to radiation in the current week (R² = 0.56). In addition, a neural network (NN) model of yield which included radiation as an input was better at predicting yield in the following week (R² = 0.70) than yield in the current week (R² = 0.57). These results indicate a lag effect of radiation on yield. Similarly, yield was more positively related to growth from the previous week (R² = 0.32) than to growth from the current week (R² = 0.17). Neural network models of daily growth at both sites (R² = 0.74, 0.69) included day of the year, temperature and CO₂ as inputs. A negative relationship between day of the year and daily growth indicates a decline in crop vigor through the measurement period. Neural network models of daily crop water use for the two sites were stronger (R² = 0.91, 0.85) than those for growth, highlighting the difference in physiological complexity between the two. A model of canopy water status as affected by environmental conditions was generated using hourly measures of tomato canopy mass change. Although the rate of canopy mass gain through the day was often constant, there were days when the plant experienced periods of reduced mass gain mid-day. On those days, the amount of deviation from a constant rate was positively related to radiation, day temperature and water use, suggesting periods of water stress. With subsequent recovery of mass gain rates late afternoon, these deviations did not affect canopy growth for the day. Overall, automated monitoring provides new information on the crop which may readily be incorporated into models of crop performance.     

Evaluating hyperspectral vegetation indices for estimating nitrogen concentration of winter wheat at different growth stages

Many hyperspectral vegetation indices (VIs) have been developed to estimate crop nitrogen (N) status at leaf and canopy levels. However, most of these indices have not been evaluated for estimating plant N concentration (PNC) of winter wheat (Triticum aestivum L.) at different growth stages using a common on-farm dataset. The objective of this study was to evaluate published VIs for estimating PNC of winter wheat in the North China Plain for different growth stages and years using data from both N experiments and farmers’ fields, and to identify alternative promising hyperspectral VIs through a thorough evaluation of all possible two band combinations in the range of 350–1075 nm. Three field experiments involving different winter wheat cultivars and 4–6 N rates were conducted with cooperative farmers from 2005 to 2007 in Shandong Province, China. Data from 69 farmers’ fields were also collected to evaluate further the published and newly identified hyperspectral VIs. The results indicated that best performing published and newly identified VIs could explain 51% (R₇₀₀/R₆₇₀) and 57% (R₄₁₈/R₄₀₅), respectively, of the variation in PNC at later growth stages (Feekes 8–10), but only 22% (modified chlorophyll absorption ratio index, MCARI) and 43% (R₇₆₃/R₇₆₁), respectively, at the early stages (Feekes 4–7). Red edge and near infrared (NIR) bands were more effective for PNC estimation at Feekes 4–7, but visible bands, especially ultraviolet, violet and blue bands, were more sensitive at Feekes 8–10. Across site-years, cultivars and growth stages, the combination of R₃₇₀ and R₄₀₀ as either simple ratio or a normalized difference index performed most consistently in both experimental (R ² = 0.58) and farmers’ fields (R ² = 0.51). We conclude that growth stage has a significant influence on the performance of different vegetation indices and the selection of sensitive wavelengths for PNC estimation, and new approaches need to be developed for monitoring N status at early growth stages.     

Response of lactating cows to supplemental rumen protected methionine and Niacin

Eight Chinese Holstein cows were used in a 4 × 4 Latin square design to determine the effects of rumen protected methionine (RPMet) and Niacin on milk yield and milk composition of lactating cows with 14 d adaptation and 6-d sampling periods. The cows were fed the control diet or the control diet plus RPMet (25 g·⁻¹), niacin (6 g·⁻¹), or RPMet (25 g·⁻¹) + niacin (6 g·⁻¹). The results showed that RPMet supplementation in the diet increased 4% fat corrected milk (FCM) yield (P < 0.05) and milk fat percentage (P < 0.05). However, supplemental RPMet had no effect on the solid non fat (SNF) (P > 0.05) and lactose percentage (P > 0.05). Dietary niacin supplementation increased milk yield (P < 0.05), milk protein percentage (P < 0.05) and lactose percentage (P < 0.05), but had no effect on milk fat percentage (P > 0.05) and SNF (P > 0.05). RPMet supplementation in the diet of lactating cows significantly decreased serum urea nitrogen (P < 0.01) and glucose contents (P < 0.05), but had no effects on nonesterified fatty acids (NEFA), total cholesterol and triglyceride (P > 0.05). Niacin supplementation influenced the contents of glucose and NEFA in serum, but had no effects on the urea nitrogen, total cholesterol and triglyceride (P > 0.05).     

Development of a yield monitoring system for citrus mechanical harvesting machines

A load cell based yield monitoring system was developed for the Oxbo citrus mechanical harvesting machines. The yield monitoring system consisted of a GPS receiver, a mass flow sensor and data processing and storage units. The mass flow sensor consisted of four load cells attached to a carbon-fiber plate which sensed the impact force created by the oranges hitting the plate. A mathematical model was developed to relate the impact force to fruit mass. Laboratory tests were conducted on a test rig that replicated the flow of oranges to measure the accuracy of the system under a controlled environment. The system performed very well under laboratory conditions (R ² = 0.99 and an average error of 3.3%). In addition, a field test was conducted in a citrus orchard in Florida to evaluate the performance of the system under field conditions. Of the 72 rows used in the field test, the first 10 rows were used to calibrate the computed weight. A correlation of R ² = 0.97 between the actual weight and the computed weight was found from the field data with an average error of 7.81%.     

Effects of phosphate fertilizer and manure on Chinese cabbage yield and soil phosphorus accumulation

The yield response of Chinese cabbage to phosphate fertilizer and manure was studied. The effect of over-application of phosphate fertilizer and manure on plant total phosphorus content and phosphorus accumulation in soil was also investigated. The experiment was arranged in a plastic barrel in the field for two years. Application of phosphate fertilizer at the rates of 150–600 mg·kg⁻¹ gave a yield increase of 14.9%–21.5% of Chinese cabbage. Application of manure at the rates of 33.3–-133.2 g·kg⁻¹ gave a yield increase of 18.2%–25.9%of the crop. There was no significant difference of yield response at the rates of 150, 300 and 600 mg·kg⁻¹ phosphate fertilizer, and no significant yield response to the application of phosphate fertilizer after applying manure. The total P content in Chinese cabbage was increased gradually with the rate increase of phosphate fertilizer and manure. Phosphorus was absorbed luxuriously by the plant with over-application phosphate fertilizer and manure. The content of total-P, Olsen-P, water-soluble P, biological available P in the soil was increased with the rate of phosphate fertilizer and manure. Organic phosphorus in the soil was increased by the application of manure. Olsen-P had high correlations with water-soluble-P and biological available-P, but there was a poor relationship between Olsen-P and organic-P. __________ Translated from Scientia Agricultura Sinica, 2006, 39(10): 2147–2153 [译自: 中国农业科学]     

Site-specific management of limiting nutrients in peanut (Arachis hypogaea) on the Texas High Plains

Nutrient data obtained from soil chemical tests were analyzed in an activity analysis model to identify limiting factors in peanut production on the Texas High Plains. A production function was estimated for the study field, and limiting factors were identified at individual sites where the production function indicated that yield did not respond. The estimated production function also enabled us to conduct a cost-return analysis of variable- and blanket-rate fertilizer applications. The results showed that peanut yields did not respond to most of the nutrients included in the study, which confirmed conclusions from previous studies in the study region. Calcium and nitrogen were the only two limiting factors identified in this study. Significant economic returns could be obtained by site-specific fertilizer application. The average economic return from variable-rate calcium fertilizer application was $27.84 ha⁻¹ and from blanket-rate it was $10.73 ha⁻¹. The return from variable-rate nitrogen fertilizer application was about $20 ha⁻¹ and from a blanket-rate it was about $14 ha⁻¹. There seems to be quite a strong economic incentive to adopt variable-rate application for calcium and nitrogen fertilizer application.

Effects of exogenous spermidine on the photosynthesis of Cucumis sativus L. seedlings under rhizosphere hypoxia stress

With water culture, this paper studied the effects of exogenous spermidine (Spd) on the net photosynthetic rate (P _n), intercellular CO₂ concentrations (C _i), stomatal conductance (G _s), transpiration rate (T _r), apparent quantum yield (Φ _c), and carboxylation efficiency (CE) of cucumber seedlings under hypoxia stress. The results showed that P _n decreased gradually under the hypoxia stress, and reached the minimum 10 days later, which was 63.33% of the control. Compared with that of the hypoxia-stressed plants, the P _n 10 days after the application of exogenous Spd increased by 1.25 times. A negative correlation (R ²=0.473−0.7118) was found between _{P n} and C _i, and G _s and T _r changed in wider ranges, which decreased under the hypoxia-stress, but increased under the hypoxia-stress plus exogenous Spd application. There was a significant positive correlation between G _s and T _r (R ²=0.7821−0.9458), but these two parameters had no significant correlation with P _n. The hypoxia stress induced a decrease of Φ _c and CE by 63.01% and 72.33%, respectively, while the hypoxia stress plus exogenous Spd application made Φ _c and CE increase by 23% and 14%, respectively. The photo-inhibition of cucumber seedlings under hypoxia stress was mainly caused by non-stomatal inhibition, while the exogenous Spd alleviating the hypoxia stress by repairing photosynthesis systems. __________ Translated from Chinese Journal of Applied Ecology, 2006, 17(9): 1609–1612 [译自: 应用生态学报]     

Comparison of passive and active canopy sensors for the estimation of vine biomass production

Recent advances in optical designs and electronic circuits have allowed the transition from passive to active proximal sensors. Instead of relying on the reflectance of natural sunlight, the active sensors measure the reflectance of modulated light from the crop and so they can operate under all lighting conditions. This study compared the potential of active and passive canopy sensors for predicting biomass production in 25–32 randomly selected positions of a Merlot vineyard. Both sensors provided estimates of the normalized difference vegetation index (NDVI) from a nadir view of the canopy at veraison that were good predictors of pruning weight. Although the red NDVI of the passive sensors explained more of the variation in biomass (R ² = 0.82), its relationship to pruning weight was nonlinear and was best described by a quadratic regression (NDVI = 0.55 + 0.50 wt−0.21 wt²). The theoretically greater linearity of the amber NDVI-biomass relationship could not be verified under conditions of high biomass. The linear correlation to stable isotope content in leaves (¹³C and ¹⁵N) provided evidence that canopy reflectance detected plant stresses as a result of water shortage and limited fertilizer N uptake. Thus, the canopy reflectance data provided by these mobile sensors can be used to improve site-specific management practices of vineyards.     

规模化奶牛场泌乳牛粪便氮磷含量预测模型研究

为了探讨基于泌乳牛日粮营养成分及其基本生产状况预测粪便氮磷含量的可行性,建立粪便总氮（fecal nitrogen,FN）、粪便总磷（fecal phosphorus,FP）含量的预测模型。本试验以中国荷斯坦奶牛为研究对象,选取天津市具有代表性的 7 家规模化奶牛场为采样点,利用问卷调查收集了 20 组泌乳期奶牛日粮营养成分及基本生产状况等基础数据,并采集了 60 份粪便样品,测定其氮磷含量。选取其中 14 组泌乳期奶牛日粮营养成分及基本生产状况等基础数据和 48 份泌乳牛粪便的氮磷含量,利用 SAS 统计分析软件,对其进行相关性分析和回归分析,建立预测模型。结果表明：日粮有机质摄入量（organic matter intake,OMI）和粗脂肪摄入量（crude fat intake,CFi）与泌乳牛粪便总氮含量有显著的正相关性,相关系数分别为 0.836 和 0.705。泌乳牛体重（body weight,BW）与粪便总磷含量呈负相关性,相关系数为-0.525。利用多元线性回归分析建立的预测模型的决定系数 R² 显著高于一元线性回归方程。其中基于泌乳牛产奶量（milk yield,MY）,产奶天数（days in milk,DIM）,日粮有机质摄入量 OMI 和氮摄入量（nitrogen intake,NI）建立的粪便总氮含量的预测模型的决定系数 R² 可达 0.96（P约0.001）,预测方程为：y=0.43+0.29×MY+0.02×DIM+0.92×OMI-13.01×NI。粪便总磷含量的预测模型的决定系数 R² 相对低于总氮含量的预测模型,最高为 0.62（P约0.10）,预测方程为：y=22.97-0.026×BW-4.02×NI+14.63×PI（phosphorus intake,PI）。最后利用 6 组泌乳牛日粮营养成分及其基本生产状况的基础数据和对应的 18 份粪便样品的氮磷含量对最优预测模型进行了外部验证。结果表明,粪便总氮含量和总磷含量的预测值与测定值间的相对误差分别为1.62%和 3.81%,预测标准差分别为 0.70 mg·g^-1 和 0.68 mg·g^-1,模型取得较理想的预测结果。     

Regional model for nitrogen fertilization of site-specific rainfed corn in haplustolls of the central Pampas,Argentina

In semi-arid regions, soil water and nitrogen (N) are generally limiting factors for corn (Zea mays L.) production; hence, implementation of appropriate N fertilization strategies is needed. The use of precision agriculture practices based on specific site and crop properties may contribute to a better allocation of fertilizer among management zones (MZ). The aim of this study was to develop a model for diagnosis of N availability and recommendation of N fertilizer rates adjusted to MZ for dryland corn crops growing in Haplustolls. The model considered variability between MZ by including site-specific variables [soil available water content at sowing (SAW) and Available Nitrogen (soil available N-NO₃ at planting + applied N, Nd)] using spatial statistical analysis. The study was conducted in Córdoba, Argentina in Haplustolls and consisted in four field trials of N fertilizer (range 0–161 kg N ha⁻¹) in each MZ. The MZ were selected based on elevation maps analysis. Grain yields varied between MZ and increased with larger SAW and Nd at sowing. Grain responses to Nd and SAW in any MZ were not different between sites, allowing to fit a regional model whose parameters (Nd, Nd², SAW, SAW²) contributed significantly (p < 0.001) to yield prediction. Agronomical and economically optimum N rates varied among MZs. However, the spatial variability of optimum N rates among MZs within sites was not enough to recommend variable N fertilizer rates instead of a uniform rate. Variable N fertilizer rates should be recommended only if variability in SAW and soil N among MZ is greater than that found in this work.     

Influences of nitrogen fertilizer application rates on radish yield, nutrition quality, and nitrogen recovery efficiency

Radishes (Raphanus sativus L.) were grown in plastic pots in a screenhouse to investigate the influences of nitrogen fertilizer application rates (NFAR) on yield, nitrate content, nitrate reductase activity (NR), nutrition quality, and nitrogen recovery efficiency (NRE) at commercial mature stage. Five N-rate treatments, 0.644, 0.819, 0.995, 1.170, and 1.346 g·pot⁻¹, were set up in the screenhouse pot experiments, and nitrogen fertilizer (unlabeled N and ¹⁵N-labeled fertilizer) was applied as basal dressing and topdressing, respectively. The results indicated that the fresh and dry weight yields of radish increased with the increase of NFAR at the range of 0.099 to 0.180 g N·kg⁻¹ soil, decreased at 0.207 g N·kg⁻¹ soil, and accordingly there was a significant quadratic relationship between the fresh and dry weight yields of radish and the NFAR. At the high addition of urea-N fertilizer, the nitrate content accumulated in the fleshy roots and leaves due to the decline in NR activity. From 0.644 to 0.819 g N·pot⁻¹ NR increased most rapidly, the highest NR activity occurred at 0.819 g N·pot⁻¹, and the lowest NR activity happened at 1.346 g N·pot⁻¹. Soluble sugar and ascorbic acid initially increased to the highest value and then decreased, and, contrarily, crude fiber rapidly decreased with the increase of NFAR. Total N uptake (TNU), N derived from fertilizer (N_dff), and N derived from soil (N_dfs) in radish increased, except that N_dfs relatively and slightly decreased at the rate of 0.207 g N·kg⁻¹soil. The ratio of Ndff to TNU increased, but the ratio of Ndfs to TNU as well as NRE of N fertilizer decreased with the increase of NFAR. Therefore, the appropriate NFAR should be preferably recommended for improving the yields and nutrition qualities of radish and NRE of N fertilizer. These authors contributed equally to this work