Double cropping of potatoes in a semi-arid environment: the association of ground cover with tuber yields

Summary The association of ground cover and ground cover duration with fresh- and dry-weight potato tuber yields in a semi-arid Mediterranean climate, was investigated. Cultivars of different maturity classes were tested under the contrasting climatological conditions of the spring and autumn seasons. The correlation coefficients of ground cover (GC) and ground cover duration (GCD) with fresh- and dry-weight tuber yields were lower for the autumn than for the spring season. In both seasons, high yields were positively correlated with high GCD. However, variation in tuber yields was evident in cultivars with similar GCD, indicating the involvement of factors other than ground cover and light interception in tuber yield. This investigation was supported by a grant from the Ministry of Foreign Affairs, Technical Assistance Department, Netherlands.     

Light use efficiencies of potato cultivars with late blight (Phytophthora infestans)

Summary Potato cultivars of different maturity classes and levels of resistance toPhytophthora infestans were grown under several disease intensities in three field trials. Seasonal courses of ground cover by green foliage and final tuber yields were determined. Light use efficiencies (LUE) were calculated from regression analyses of yield on cumulative light interception. Late blight reduced tuber yields by decreasing cumulative light interception without affecting LUE. No differences in LUE between cultivars or cultivar classes were detected. Therefore, the maintenance of green leaf area is important when breeding potatoes for optimal performance in the presence of late blight. The results support the hypothesis that the correlation between lateness and reported resistance of potato cultivars is due to the vigorous foliage growth of late cultivars.     

马铃薯无性一代植株性状相关及通径分析

本文对马铃薯30个杂交组合无性一代的14个性状与单株产量的相关关系作了估算,其中无效生育期、播后74天和92天冠层覆盖度、平均冠层覆盖度、最高冠层覆盖度、有效生育期、单株块茎数、单块重8个性状与单株产量的相关性达显著或极显著水平。进而对影响单株产量(y)的平均冠层覆盖度(x_1),有效生育期(x_2)、单株块茎数(x_3)、单个块茎重(x_4)进行通径分析。结果表明,该4个性状决定单株产量变异的94.61％,说明这4个性状是影响单株产量的决定因素。     

A Robust Potato Model: LINTUL-POTATO-DSS

In 1994, LINTUL-POTATO was published, a comprehensive model of potato development and growth. The mechanistic model simulated early crop processes (emergence and leaf expansion) and light interception until extinction, through leaf layers. Photosynthesis and respiration in a previous crop growth model—SUCROS—were substituted by a temperature-dependent light use efficiency. Leaf senescence at initial crop stages was simulated by allowing a longevity per daily leaf class formed, and crop senescence started when all daily dry matter production was allocated to the tubers, leaving none for the foliage. The model performed well in, e.g., ideotyping studies. For other studies such as benchmarking production environments, agro-ecological zoning, climatic hazards, climate change, and yield gap analysis, the need was felt to develop from the original LINTUL-POTATO, a derivative LINTUL-POTATO-DSS with fewer equations—reducing the potential sources of error in calculations—and fewer parameters. This reduces the number of input parameters as well as the amount of data required that for many reasons are not available or not reliable. In LINTUL-POTATO-DSS calculating potential yields, initial crop development depends on a fixed temperature sum for ground cover development from 0% at emergence to 100%. Light use efficiency is temperature dependent. Dry matter distribution to the tubers starts at tuber initiation and linearly increases up to a fixed harvest index which is reached at crop end. Crop end is input of the model: it is assumed that the crop cycle determined by maturity matches the length of the available frost-free and or heat-free cropping season. LINTUL-POTATO-DSS includes novel calculations to explore tuber quality characteristics such as tuber size distribution and dry matter concentration depending on crop environment and management.     

NET PHOTOSYNTHESIS AND LEAF AREA INDEX RELATIONSHIPS IN SWARDS OF DACTYLIS GLOMERATA UNDER CONTRASTING DEFOLIATION REGIMES

Net photosynthesis per unit area of ground surface was determined at saturating light energy levels in Dactylis glonwrata swards over a wide range of leaf area indices (LAI). The relationship between net photosynthesis and LAI was influenced by the particular defoliation regime to which the sward was subjected. In most instances net photosynthesis and LAI were linearly related, with defoliation regime influencing both the slope and intercept of the regression. However, a defoliation regime which left leaves below 3 inches (7.5 cm) resulted in a curvilinear relation. The net photosynthesis-LAI relationships were compared with the DM production of the swards on which they were obtained. Differences in these relationships did not entirely explain the differences in sward yield. The significance of these findings is discussed with reference to the theories of light interception and pasture growth.     

Monitoring grass swards using imaging spectroscopy

The potential of an imaging spectroscopy system with high spatial (0·16–1·45 mm²) and spectral resolution (5–13 nm) was explored for monitoring light interception and biomass of grass swards. Thirty‐six Lolium perenne L. mini‐swards were studied for a total of eleven consecutive growth periods. Hyperspectral images and light interception (LI) were recorded twice weekly. On two dates ground cover was scored visually (GC_v). At harvest, leaf area index (LAI), fresh‐matter yield and dry‐matter yield (DMY) were determined. Classification of images yielded several estimates of the image ground cover (GC_i) and the index of reflection intensity (IRI). The GC_i was highly correlated with GC_v ( = 0·94), LAI ( = 0·88) and LI ( = 0·95, for dense swards under cloudy skies). However, the relationship between GC_i and LI depended on sky conditions and sward structure. Under cloudy skies, LI was linearly related to GC_i, whereas under clear skies, this relation was logistic. Regression analysis of GC_i and yields showed correlations with of between 0·75 and 0·82. The mean error of DMY estimates was 340 kg. In conclusion, estimates of GC_i and IRI can be used to predict DMY, even for high yield levels (up to 3500 kg DM ha^?1), allowing accurate, non‐destructive monitoring of biomass and light interception of grass swards.     

Assessment of seasonal dry-matter yield and quality of grass swards with imaging spectroscopy

The potential of imaging spectroscopy for the assessment of seasonal dry‐matter (DM) yield and sward quality was studied. Relationships between spatial heterogeneity of tiller density, light interception, ground cover and seasonal DM yield were developed. Sward heterogeneity was quantified by the spatial standard deviation of ground cover and of logarithmically transformed ground cover, and patterns in ground cover transects were quantified by wavelet entropy. An experiment was conducted with eight control (C) swards, eight naturally damaged (ND) swards and twelve artificially damaged (AD) swards. Swards were established in containers and spectroscopic images were recorded twice weekly. Seasonal DM yield was linearly related to a combination of means of ground cover and index of reflection intensity (r² = 0·93). Spatial variation of tiller density was larger for AD and ND swards than for C swards. Values of the spatial standard deviation of ground cover and wavelet entropy were larger for AD and ND swards than for C swards. A single spatial standard deviation of ground cover value of 13% discriminated ND and AD swards from C swards. Seasonal means of wavelet entropy (r² = 0·70) and the spatial standard deviation of ground cover (r² = 0·63) at harvest were linearly related to seasonal DM yield. It is concluded that imaging spectroscopy can be used for assessing seasonal DM yield and sward heterogeneity.     

超高产条件下玉米产量及冠层结构

2011~2012年,选用郑单958为供试材料,以传统栽培模式为对照(CK),研究超高产栽培条件下春玉米的冠层结构。结果表明,超高产条件下春玉米产量及有效穗数均显著高于对照;玉米在超高产栽培条件下,其群体叶面积指数(LAI)均高于传统栽培模式(CK),且LAI最大值的持续天数比CK长。棒三叶及棒三叶以上叶增加幅度明显,与CK均达到显著水平;超高产栽培条件下玉米叶倾角明显小于CK,叶向值增大,群体受光态势较好。叶片光合速率(Pn)均随生育时期的推移而不断降低,在全生育期超高产栽培条件均高于CK,并且在大喇叭口期差异显著;整个生育时期超高产栽培条件的光合势均高于CK。超高产栽培LAI持续天数长,叶倾角小,叶向值大,进而改善玉米群体受光态势,提高叶片光合能力,具有高光效的冠层结构。     

实地氮肥管理下的水稻生长发育和养分吸收特性

 以代表性水稻品种为材料，研究了实地氮肥管理模式下水稻的生长发育和养分吸收规律。与农民习惯施肥方法相比，实地氮肥管理在产量不降低甚至有所提高的前提下可以较大幅度地降低施氮量。实地氮肥管理水稻有效穗数有所下降，但其分蘖成穗率明显提高。穗分化前实地氮肥管理水稻叶面积指数和根质量低于农民习惯施肥法，抽穗后结果则相反。实地氮肥管理提高了抽穗期水稻的有效叶面积和高效叶面积的比率、抽穗至成熟的干物质积累、抽穗后根冠比和剑叶的光合速率以及齐穗期群体透光率。实地氮肥管理水稻对氮、磷、钾的吸收高峰均出现在穗分化至抽穗期，此阶段氮、磷、钾的吸收量约占最终总吸收量的45.6%~46.2%、39.6%~43.6％和44.2%～45.2％，均明显高于农民习惯施肥方法。对实地氮肥管理产量提高原因及养分吸收规律进行了讨论。     

Assessing broadband vegetation indices and QuickBird data in estimating leaf area index of corn and potato canopies

Leaf area index (LAI) is a key biophysical variable that can be used to derive agronomic information for field management and yield prediction. In the context of applying broadband and high spatial resolution satellite sensor data to agricultural applications at the field scale, an improved method was developed to evaluate commonly used broadband vegetation indices (VIs) for the estimation of LAI with VI–LAI relationships. The evaluation was based on direct measurement of corn and potato canopies and on QuickBird multispectral images acquired in three growing seasons. The selected VIs were correlated strongly with LAI but with different efficiencies for LAI estimation as a result of the differences in the stabilities, the sensitivities, and the dynamic ranges. Analysis of error propagation showed that LAI noise inherent in each VI–LAI function generally increased with increasing LAI and the efficiency of most VIs was low at high LAI levels. Among selected VIs, the modified soil-adjusted vegetation index (MSAVI) was the best LAI estimator with the largest dynamic range and the highest sensitivity and overall efficiency for both crops. QuickBird image-estimated LAI with MSAVI–LAI relationships agreed well with ground-measured LAI with the root-mean-square-error of 0.63 and 0.79 for corn and potato canopies, respectively. LAI estimated from the high spatial resolution pixel data exhibited spatial variability similar to the ground plot measurements. For field scale agricultural applications, MSAVI–LAI relationships are easy-to-apply and reasonably accurate for estimating LAI.     

Yield prediction using the SUBSTOR-potato model under Argentinian conditions

Summary The use of crop simulation models to predict yield, associated with decision support systems such as Decision Support System for Agrotechnology Transfer (DSSAT), are useful tools to test different management strategies. The potato growth model included in DSSAT is SUBSTOR-potato. To evaluate its performance in Argentina it was calibrated and validated using experimental results from different sites and years. Cultivar-specific coefficients were obtained during calibration. Validation based on several independent sets of field data, including cvs Huinkul, Kennebec, Mailén and Spunta showed good agreement (R²=0.915; n=24) between observed and simulated values in normal ranges of tuber yields. However, when the input parameter maturity date was not taken into account, tuber yields were overvalued due to an overestimation of LAI values during maturation. To solve this problem, a genetic coefficient for the duration of tuber filling needs to be included in the model.     

Irrigation effects on elephant grass morphology,and its genotype-dependent responses

This study hypothesised that different elephant grass genotypes respond differently in terms of their morphological development to irrigation. The objective of this study was to evaluate how water availability could affect the morphological development of different genotypes of elephant grass. The treatments consisted of four genotypes of elephant grass [Cenchrus purpureus (Schumach.) Morrone], managed under irrigation or not, during a two-year field trial. The experiment was arranged in a randomised block design in a split-plot, with four replicates per treatment (n = 4). Between the genotypes, two of them were classified as tall-sized (IRI 381 and Elephant B), and two as dwarfs (Taiwan A-146 2.37 and Mott). A three-way interaction between season, irrigation, and genotype affected the variables plant height, stem diameter, number of dead tillers, light interception (LI), and leaf area index (LAI) (p < .05). The morphological development of all genotypes was negatively impacted by the dry season. All genotypes grew taller during the rainy season (p < .05) and had a greater light interception (62%–80%) compared to the dry period (28%–59%). The genotype Mott, showed comparable LI and LAI to the tall-sized genotypes, whilst Taiwan A-146 2.37 was characterized by the lowest values, despite being the genotype with the greatest tiller density (60 tillers m⁻²) (p < .05). The use of irrigation mitigated the negative effects of the dry season on the plants, however, the type and size (tall vs. dwarf) of the elephant grass genotypes defined the extent of the responses to the use of the irrigation during the dry period.     

宽幅带播对大穗型冬小麦冠层特征及产量的影响

为了解宽幅带播在小麦种植上的应用效果,在大田条件下,以兰考矮早八为材料,研究了宽幅带播种植对大穗型冬小麦冠层特征及产量的影响.结果表明,与常规条播比较,宽幅带播的小麦群体叶面积指数、冠层光截获量和相对湿度较高,而冠层温度较低,穗数显著增加,产量提高0.47％～13.70％.宽幅带播下随着行距增大,叶面积指数、光截获量和湿度降低,而冠层温度升高,穗数和穗粒数减少,千粒重增加,最终产量降低.宽幅带播下15 cm行距可作为大穗型冬小麦品种的适宜行距配置.     

利用RADARSAT-2雷达数据与改进的水云模型反演冬小麦叶面积指数

利用微波遥感反演植被参数往往受到植被分布不均、稀疏植被覆盖、地表裸土等因素影响,导致微波遥感用于农业参数估计的效果不佳。为解决微波遥感反演地表植被参数的问题,本研究在原有的水云模型基础上引入植被覆盖度以及裸土对于雷达后向散射系数的直接作用信息,提出一种改进的水云模型,并充分考虑地表植被的覆盖分布情况,结合地面实测数据及RADARSAT-2雷达数据对改进模型进行验证,然后根据改进模型通过查找表法反演出植被含水量,最后利用叶面积指数与植被含水量的经验关系间接得到叶面积指数的估测值。结果表明,改进的水云模型对后向散射系数的模拟精度比原有的水云模型精度高,模拟的决定系数在HH和VV极化时分别为0.850和0.739,均方根误差分别为0.918dB和1.475dB。由此可见,改进的模型对研究区植被条件更为敏感,能够较好地分离出植被与土壤信息对雷达后向散射系数的影响,同时利用其反演得到的叶面积指数精度较高,决定系数达到0.841,均方根误差为0.233。     

Hill to hill variations in tuber yield of potatoes in Alberta

The hill to hill variation in tuber yield and mainstem number was studied on 18 potato farms. There were up to 14-fold differences in the tuber yield per hill among plants of Norland, Russet Burbank, Norchip, Carlton and Alaska Red. The mainstem number was more variable than tuber weight per hill in Norland, Russet Burbank and Alaska Red. However, the opposite was true in Norchip and Carlton. In nearly all comparisons, the number of tubers per hill was less variable than tuber weight and mainstem number per hill. The total variation in tuber weight found in about 50% of the samples could be explained by the variance of hills within rows. Even in samples where an added variance component due to differences among rows was present, relatively more variation occurred within than among rows. The correlation coefficients between the number of mainstems and tuber weight per hill were positive but significant (P&< 0.05) only in Norland and Norchip. The correlation coefficients between the number of mainstems and number of tubers per hill were also positive but slightly higher and significant (P<0.01) in all 5 cultivars. The coefficient of determination values indicated that variation in cut seed piece weight explained only about 10% of the total variation in tuber weight harvested per hill. At a spacing of 30 cm within the row, a major proportion of hill to hill variation in tuber yield had to be explained by factors other than the seed piece weight.     

Effects of genetic improvements on grain yield and agronomic traits of winter wheat in the Yangtze River Basin of China

Wheat is an important food crop worldwide. Genetic improvements have contributed much to wheat production since the 1960s. Verifying the evolution of agronomic traits and the physiological basis of grain yield will facilitate breeders and agronomists in developing new wheat cultivars, with the aim of stable and high yields. Thirty-five wheat cultivars, bred or widely planted in the Yangtze River Basin from 1950 to 2005, were grown in field experiments under three N rates (0, 112.5, and 225 kg N ha⁻¹) from 2006 to 2009 in Nanjing, China. Wheat grain yield, kernels per spike, 1000-kernel weight (TKW), and harvest index (HI) increased linearly with cultivar development from the 1950s to the 2000s, whereas spikes per unit land decreased significantly with cultivar development during the same period, and stabilized with further genetic improvements in cultivars. Grain yield, kernels per spike, and TKW differed with N rate and with cultivar. Grain yield, spikes per unit land, and kernels per spike increased significantly with increasing N fertilizer, but TKW and HI decreased. Cultivar height decreased with cultivar development from the 1950s to the 1980s, and remained relatively stable in subsequent cultivars. The proportion of the length of the top internode to total plant height increased with cultivar development from the 1950s to the 1980s and thereafter fell, while the length of the basal internode (BI) maintained a shortening trend. Leaf area per culm, leaf area index (LAI), net photosynthetic rate (Pn), and photosynthetic activity duration (PAD) of the flag leaf increased with cultivar development. Leaf area, LAI, and Pn increased significantly with increasing N fertilizer, while PAD did not. Single spike yield increased linearly with genetic development in cultivars, and these increases mainly resulted from increasing kernel number and weight, which were closely related to source size and cultivar. Grain yield was positively correlated to leaf area, LAI, Pn_Max, PAD, and single spike yield; single spike yield was positively correlated to leaf area, LAI, Pn_Max, and PAD, suggesting that grain yield improvements were mainly associated with improvements in the source (leaf area, LAI, Pn, PAD, etc.) and sink (single spike yield). Sink-source ratios increased with genetic development of cultivars, suggesting that productivity per leaf improved and that sink-source relationships have reached close to optimum in the Yangtze River Basin. Furthermore, breeding for high yield should be related to improvement in kernels per spike and TKW per unit land and increased sink-source ratios with a feasible LAI, and N fertilizer management should be considered during breeding for higher yields.     

Estimating potato leaf area index for specific cultivars

Summary The growth and duration of crop leaf area determines the amount of solar radiation intercepted by the canopy and therefore influences the extent of photosynthesis, evaporation, transpiration and final dry matter yield. The objective of this study was to develop cultivar specific relationships to estimate the daily leaf area index (LAI) for the potato crop (Solanum tuberosum L.) that included the effects of available soil water. The model is divided into three LAI growth stages, the durations of which are partially related to potato heat units (PHU). The LAI in the first stage is estimated from a cultivar specific leaf area-based radiation use efficiency index with a soil water reduction factor. The second stage involves the maintenance of a constant LAI with the duration related to both PHU and a soil water index that can accelerate senescence. The final stage includes a decrease in the LAI from a maximum to zero in response to a cultivar specific PHU accumulation. Model simulations compared favourably with independent LAI measurements obtained with a LI-COR plant canopy analyzer over two seasons.     

Intercropping cassava with soybean cultivars of varying maturities

Our previous work has shown that early-maturing soybean is suitable for intercropping with vassava at a high latitude (27°S) in south-east Queensland, Australia, as it does not effect the tuber yield. The present study examines whether later-maturing cultivars of soybean with higher yield potential might be more productive. Plant arrangement for cassava was the same in sole crop and in intercrop, while two soybean rows in every six rows were replaced by a row of cassava in intercropping.All soybean cultivars dominated intercropped cassava, and their dry-matter growth and seed yield were not affected by competition with cassava. Growth of cassava was, on the other hand, severely restricted by intercropped soybean, particularly by late-maturing types. After removal of early-maturing soybean, cassava recovered quickly to produce high leaf-area and effectively intercepted solar radiation. Consequential high total dry-matter production, combined with high assimilate allocation to tubers, resulted in tuber yield at the final harvest similar to that in sole cassava. After the removal of late-maturing soybean, however, recovery was poor, and with a short growing season remaining, tuber yields were only 50–60% of that of sole cassava.In addition to their adverse effect on cassave growth, late-maturing cultivars were not suitable as an intercrop because of low harvest indices and low light-conversion efficiency (dry matter produced per unit intercepted radiation), although total light interception during the whole growth of cassava/soybean intercrop was similar to that of sole cassava. The low overall light-conversion efficiency in intercropping with late-maturing cultivars was due to very low dry-matter production of soybean during pod-filling when light interception was still high.     

Soil water stress and the growth and yield of potato plants grown from microtubers and conventional seed tubers

Tuber yields of potato plants grown from microtubers in fields are more variable than yields from conventional seed tubers (CT). One reason could be their higher susceptibility to water stress. This study clarified the effect of soil water stress from 1 month after emergence on the growth and yield of plants grown from conventional seed tubers and microtubers in fields. Microtubers (0.5–3 g) and conventional seed tubers (50 g) were grown in Hokkaido, Japan, over three field seasons. One month after emergence, poly-shelters were placed over the plots to prevent rainfall, and either irrigated (wet plot) or non-irrigated (dry plot) treatments were formed. At mid-flowering (about 50 days after emergence) leaf area index (LAI) in microtuber plants was decreased relatively more due to soil water stress than LAI in conventional seed tuber plants. However, at maximum shoot growth (about 80 days after emergence) both microtuber and conventional seed tuber plants had a similar relative decrease in LAI due to soil water stress. At mid-flowering and maximum shoot growth microtuber and conventional seed tuber plants had reduced stomatal conductance due to soil water stress, but the reduction in stomatal conductance was greater in conventional seed tuber plants than in microtuber plants. Microtuber and conventional seed tuber plants had similar root development at maximum shoot growth. Tuber production from mid-flowering until plant maturity was similarly affected by soil water stress in microtuber and conventional seed tuber plants. At harvest, plants affected by soil water stress had about 87% of the tuber dry weight of irrigated plants. We conclude, that the greater variation on tuber yield of microtuber plants cannot be attributed to soil water stress from 1 month after emergence.     

Sunflower simulation using the EPIC and ALMANAC models

Modeling of sunflower (Helianthus annuus L.) is challenging because the crop species combines high yield potential with great adaptability. This paper surveys recent modeling-related research on sunflower phenology, growth, and yield. Simulations of sunflower by two closely related models, and almanac, are described. Phenology was predicted with growing degree days with a 6°C base temperature (GDD₆) summed from sowing to maturity, assuming anthesis occurred when 0.62 of the total GDD₆ had accumulated. Growth simulation involved leaf area index (LAI) development, light interception and radiation-use efficiency (RUE). Inclusion of a vapor pressure deficit (VPD) effect appeared to make RUE more general. A modified harvest index approach was used to simulate seed yields. The and models gave reasonable yield simulations over a wide range of environments and management options. The models should be valuable both for assessing the impacts of different management schemes and for identifying subject areas where additional basic research is needed.