Photosynthetically Active Radiation Interception Research Articles

Manipulating crop row orientation and crop density to suppress Lolium rigidum

SummaryLight is an important resource that crops and weeds compete for and so increased light interception by the crop can be used as a method of weed suppression in cereal crops. This research investigated the impact of altered availability of photosynthetically active radiation (PAR) (from crop row orientation or seeding rate) on the growth and fecundity of Lolium rigidum. Wheat and barley crops were sown in an east–west (EW) or north–south (NS) direction, at a high or low seeding rate, in three field trials in 2010 and 2011 (at Merredin, Wongan Hills and Katanning, Western Australia). The average PAR available to L. rigidum in the inter‐row space of EW crops compared with NS crops was 78% to 91% at crop tillering, 39% to 56% at stem elongation, 28% to 53% at boot/anthesis and 41% to 59% at grain fill. Reduced PAR in the EW crop rows resulted in reduced L. rigidum fecundity in five of the six trials (average of 2968 and 5705 L. rigidum seeds m−2 in the EW and NS crops). Availability of PAR was not influenced by seeding rate, but the high seeding rate reduced fecundity in three of the six trials (average of 3354 and 5092 seeds m−2 in the crops with high and low seeding rate). Increased competitive ability of crops (through increased interception of PAR or increased crop density) was highly effective in reducing L. rigidum fecundity and is an environmentally friendly and low cost method of weed suppression.

IMPROVED TRAINING AND PRUNING TECHNIQUES INCREASED PRODUCTIVITY OF 'ROCHA' PEAR

‘Rocha’ pear yield has been improving steadily in the last decades, through intensification and refinement of cultural practices. Three orchards P1 (2700 trees ha-1), P2 (3600 trees ha-1) and P3 (5400 trees ha-1) were planted in 2004, 1999 and 2004, respectively, to determine the adaptability of ‘Rocha’ pear to high density producing models. During four years an experiment was conducted to study the effects of alternative training (P1 and P3) and pruning techniques (P2). Three training treatments consisted of alternate axis-tilt angles of 0, 12 and 17° in orchard P1 and 0, 5 and 10° in orchard P3. Pruning treatments consisted of three levels of pruning intensity (non-pruning, light and severe pruning). Extensive measurements were done in the soil, plant and atmosphere. Emphasis was on the light environment, using a ceptometer, net photosynthesis, light and CO2 response curves of individual leaves, using an IRGA, biomass partitioning, fruit growth and quality and final yield. ‘Rocha’ showed very good adaptation to high-tree density. The four-year average productivity of P1-orchard increased with axis-tilt; it was respectively 52.9, 62.5 and 70.0 t ha-1. The four-year average productivity of P3-orchard was higher for the higher axis tilt (86.2 t ha-1), but there was no improvement with axis-tilt in the other cases. Pruning treatments resulted in productivities of 77.1, 106.6 and 105.7 t ha-1 for non-, light and severe pruning. Both tilt angle and pruning intensity increases resulted in higher fruit grades due to a significant positive effect on fruit growth. Axis-tilt increased PAR interception and photosynthetic rates, mainly deep inside the canopy. At solar noon, the fraction of intercepted PAR exceeded 60% in the most effective treatments, 10% more than 0° tilt trials. ‘Rocha’ pear has shown high yield potential, and productivity and fruit quality increased with appropriate combination of planting density, training and pruning techniques.

Influence of late planting on light interception, radiation use efficiency and biomass production of four sweet sorghum cultivars

As a measure of a plants ability to convert solar energy into biomass, radiation use efficiency (RUE) can be used to compare species and genotypes within species. Despite considerable research on RUE of biofuel species, few reports on sweet sorghum (Sorghum bicolor (L.) Moench.) RUE are available. Radiation use efficiency and biomass yield of four sweet sorghum genotypes (‘Dale’, ‘M 81E’, ‘Topper 76-6’, and ‘Sugar Drip’) was assessed in response to two late planting dates in a two-year study. The late planting dates would coincide with abandoning double-crop plantings of soybean following wheat. Aboveground biomass yield and RUE (gbiomassMJ−1 intercepted photosynthetically active radiation (IPAR)) was measured every two weeks beginning four weeks after planting. Two estimates of RUE were calculated differing only in growth periods used (emergence to anthesis [EA] and during rapid linear growth [Max]). Biomass yields, EA, and Max RUE were similar between years and sorghum cultivars, but differed between planting dates. Early-July plantings resulted in greater RUE than mid-July plantings. Averaged across cultivars at the first planting date both years EA and Max RUE were 3.11 and 3.96gMJ−1IPAR, respectively, compared to 2.40 (EA RUE) and 2.79gMJ−1IPAR (Max RUE) at the second planting date. Mean biomass yield across years and cultivars was 10.67 and 8.63Mgha−1 at the first and second planting dates, respectively. These results confirm expected decreases in RUE and biomass production of late-planted sweet sorghum, but also illustrate that, even when planted late, sweet sorghum efficiently converts intercepted PAR to biomass.

Radiation Interception and Use Efficiency Contributes to Higher Yields of Newer Maize Hybrids in Northeast China

A significant trend of decreasing solar radiation has been observed in Northeast China over the past six decades. Such a decline in solar radiation could negatively impact maize (Zea mays L.) production. The improved cultivated hybrids may have adapted to these changes in solar radiation. In this study, four commonly cultivated maize hybrids in Northeast China were selected for a 2‐yr field study. Two hybrids were released in the 1970s and the other two were released in the 1990s. In comparison with the maize hybrids released in the 1970s, the maize hybrids released in the 1990s exhibited significant increases in both dry matter at maturity (P < 0.05) and grain yields (P < 0.05), although the harvest index (HI) showed no significant difference. The greater dry matter accumulation was primarily responsible for the yield increase observed in the 1990s’ hybrids. The greater dry matter accumulation occurred primarily during the tasseling‐to‐maturity stage. Our results indicated significant improvements (P < 0.05) in crop growth rate and radiation use efficiency (RUE) in 1990s’ hybrids, particularly during the tasseling‐to‐maturity stage. Additionally, the net photosynthetic rate (NPR) of the ear‐leaf before 1200 h was also significantly improved in the 1990s’ hybrids. The fraction of photosynthetically active radiation (PAR) interception on the third leaf above the ear‐leaf was increased during the tasseling‐to‐maturity stage and significantly correlated with maize grain yields (P < 0.01), indicating that the increase in the fraction of PAR interception at this layer contributed to the higher grain yield in the 1990s hybrids.

Heat utilization vis-à-vis crop performance of mechanically transplanted rice (Oryza sativa L.) as affected by tillage systems and nitrogen levels

The experiment comprising of four tillage methods viz., puddling (PTR), conventional tillage without puddling (CT), reduced tillage (RT) and zero tillage (ZT) and four nitrogen levels at 0, 100, 125 and 150 kg ha-1 was conducted in a strip plot design with four replications at Punjab Agricultural University, Ludhiana during 2010 and 2011 to study the effect of tillage and nitrogen levels on productivity and heat utilization in mechanically transplanted rice. Results revealed that periodic plant height and dry matter accumulation by the crop recorded at 30, 60, 90 DAT and at harvest, leaf area index (LAI) and photosynthetically active radiation (PAR) interception by the crop at panicle emergence stage and the grain yield were statistically at par in mechanical transplanting in CT and PTR but significantly higherthan that in RT and ZT. Application of 150 kg N ha-1 recorded significantly higher LAI, PAR interception, number of tillers and grain yield than that in 0, 100 and 125 kg N ha-1. Mechanical transplanting in CT recorded highest accumulation of growing degree days (GDD) and highest heat use efficiency (HUE). The accumulated GDD and HUE increased significantly with each successive increase in nitrogen dose from 0 to 150 kg ha-1.

Tree architecture of pillar and standard peach affect canopy transpiration and water use efficiency

The development of productive high density peach orchards is often limited by the excessive vegetative growth of the trees that reduces productivity and quality. Dwarfing rootstocks are not available but upright tree architectures have been developed for high density peach production. The purpose of this study was to determine the water use efficiency of upright pillar and standard architecture peach trees in a production setting in order to understand the factors that differentiate transpiration and water use efficiency of the two tree architectures.There were no differences in leaf area index (LAI) of the pillar and standard types but the standards architecture had significantly greater leaf area density (LAD) than the pillar. There was no significant difference in the photosynthetically active radiation (PAR) response of photosynthesis (A) and transpiration (E) for the pillar and standard trees over a range of LAI's and vapor pressure deficits (VPD) for the 3 year period indicating that there was no genetic difference in gas exchange mechanisms between the genotypes of the two tree architectures. For high light conditions, the pillar and standard trees had a similar and non-significantly different E: VPD relationship for LAI<2.25, however, for LAI>2.25, the pillar had a significantly (P=0.05) greater E than the standard architecture at similar VPD levels due to the decreased LAD of the pillar architecture that more effectively distributed light within the canopy. The increased illumination and interception of PAR by the pillar canopy increased both photosynthesis and transpiration at the same WUE as the standard. The present work demonstrated that as pillar growth types are integrated into production systems, more research will be needed to efficiently schedule the water needs of the pillar architecture in order to maximize fruit size and quality due to the reduced LAD of this tree architecture and the greater illumination of the canopy interior.

DEVELOPING A PHYSIOLOGICAL BASIS FOR MODELING PEACH CANOPY PHOTOSYNTHESIS UNDER WATER STRESS CONDITIONS

Daily leaf photosynthesis was reported to be linearly related with daily leaf PAR (photosynthetic active radiation) interception, in peach trees. This relationship was considered as a fundamental step for modeling whole peach canopy photosynthesis. However, data reporting linear relationships was obtained under non-water-stressed trees. Although commercial peach orchards are usually managed under full irrigation, reduced irrigation might become inevitable in water limited areas. Water shortage is becoming increasingly frequent in peach producing areas with Mediterranean climates. Modeling the effect of water stress, on whole canopy photosynthesis, requires studies on the effect of water stress on the relationship between daily leaf photosynthesis and daily leaf light interception. We, therefore, studied the effects of water stress on the linear relationship between daily photosynthesis and light interception in a commercial ‘Ryan’s Sun’ peach orchard. Water stress was imposed during the final stage of fruit development (50 days before harvest), because irrigation restrictions usually occur mid-summer. Under full irrigation conditions, there was a linear relationship between daily intercepted PAR and daily photosynthetic CO2 assimilation. This relationship had approximately a zero y-intercept. Under water stress conditions, the y-intercept was maintained, but there was a significant decrease in daily photosynthetic CO2 assimilation rates, at high levels of daily intercepted PAR. The higher the level of water stress, the higher the reduction in CO2 assimilation. The main consequence is that linearity between daily intercepted PAR and daily photosynthetic CO2 assimilation was not maintained under severe water stress conditions. Photosynthetic radiation use efficiency (PhRUE), for all leaves of the canopy, was similar under full irrigation conditions. However, under water stress conditions, the leaves that intercepted high values of PAR had significantly reduced PhRUE. These results can facilitate modeling the effect of water stress on whole canopy photosynthesis, in peach trees.

Effect of Tillage on the Growth and Yield of Cowpea Varieties in Sudan Savanna Agroecology of Northern Nigeria

Field study was conducted during the rainy seasons (July-November) of 2007, 2008, 2009 and 2010 at the Research Farm of the International Institute of Tropical Agriculture (IITA) Minjibir, Kano State, Nigeria; to compare responses of six cowpea varieties to tillage. The treatments consisted of tillage systems (zero tillage, flat tillage and ridge tillage) as the main plot and cowpea varieties (IT89KD-391, IT90K-277-2, IT97K-461-4, IT97K-499-35, IT98K-131-2, and IT98K-506-1) as the sub-plot. The treatments were arranged as split plot laid out in a randomized complete block design with four replications. Zero tillage was significantly superior in influencing days to maturity, canopy height, intercepted Original Research Article Ewansiha et al.; ARRB, 5(3): 275-284, 2015; Article no.ARRB.2015.030 276 photosynthetic active radiation (IPAR) and leaf area index but not total dry matter and grain yield of cowpea. A positive and significant association was recorded for days to physiological maturity and canopy height across the tillage systems with a correlation coefficient of ≤ 40% for days to maturity and ≥50% for canopy height. Though flat tillage showed a positive correlation with intercepted photosynthetic active radiation (IPAR) and leaf area (LAI), but this association was not significant. However, ridge tillage showed a positive and significant correlation with IPAR and LAI (r =0.378*** and 0.384***). All the tillage systems showed a high and significant positive correlation with cowpea dry matter and fodder yield (r= 0.54*** to 0.77***). Across varieties, grain yield was better with flat tillage than zero and ridge tillage systems, with 10% yield advantage over the two. Zero and ridge tillage were similar in their effects on grain yield. Except for IPAR, LAI and total dry matter (TDM), the interaction effect of cowpea varieties and tillage systems was significant. Our result point to the fact that extensive soil tillage (especially, conventional tillage) may not be necessary for cowpea production in this agro-ecology with a high percentage of sand and a sandy loam as soil textural class. Following our result, we may recommended varieties for the different tillage systems as follows: IT98K-131-2, IT97K-461-4, IT90K-277-2, IT98K-506-1 (grain) and IT89KD-391/IT97K-4614 (best for fodder) for zero tillage system; IT90K-277-2, IT97K-499-35, IT98K-131-2 and IT98K506-1(grain) and IT89KD-391/IT97K-499-35 (best for fodder) for flat-tillage; IT98K-131-2, IT90K277-2, IT98K-506-1 and IT97K-464-4(grain) and IT90K-277-2/ IT89KD-391 (best for fodder) for ridge tillage).

Effects of Phenology-based Irrigation Scheduling and Nitrogen on Light Interception, Water Productivity and Energy Balance of Maize (Zea maysL.)

Maize (Zea mays L.) is considered as one of the diversifying options in rice fallows of eastern India. Research was conducted to study intercepted photosynthetically active radiation (IPAR), radiation utilization efficiency (RUE), latent heat flux and water productivity of the crop under different irrigation (120, 180, 240, 300 and 360 mm) and nitrogen (30, 60, 90, 120 and 150 kg N ha−1) levels and relationships were established among biomass, yield, RUE, IPAR and water productivity. The RUE of the crop ranged from 1.01 to 2.16 g MJ−1, the latent heat flux from 8.64 to 18.77 MJ m−2 day−1 and average water productivity from 0.673 to 0.983 kg m−3 under different N and irrigation levels. The difference in LAI, biomass production and yield was not significant between 120 and 150 kg N ha−1, which might be attributed to the fact that these crop attributes were not proportionately increased with the amount of additional N applied. A comparison of water productivity between the treatments receiving irrigation at flowering and milk ripegrain filling stages and not receiving irrigations at these stages with same amount of irrigation (300 mm) showed that water was more efficiently utilized when irrigation was not skipped at flowering and milk ripegrain filling stages. The RUE was higher in milk ripe stage (milk to solid conversion of endosperm, but whole kernel content is still milky liquid) and reduced during grain filling stage. This might be attributed to the reduced seed weight and grain number in case of water and N stressed plots, where partitioning of photosynthates towards grain is less that limits the RUE.

Mapping interception of photosynthetically active radiation in sweet cherry orchards

Understanding interception of photosynthetically active radiation (PAR) of individual canopies could help advanced orchard management, thus, enhance fruit productivity and quality. The objective of this research was to develop a canopy PAR interception mapping method in Y-trellis trained sweet cherry orchards. A mobile measurement system was developed for continuously collecting constant spatial resolution PAR data at varying moving speeds. A mathematical model was developed to correct the distortion of the projected canopy shadow due to time of day and/or from orchard latitude. The mapping method was evaluated at both the dormant and full canopy stages. Digital images of 10 trees were used to validate the canopy projection correction method in each test. The measurement system achieved constant spatial resolution of 0.01m·sample−1 within the entire platform speed range of 0–3.8kmh−1. For dormant stage, the relative error in branch elevation angle comparison ranged from 0.1% to 9.6% with a mean of 3.4%±3.1%, and for full canopy stage, the relative error in canopy eccentricity ranged from 1.5% to 10.3% with a mean of 4.8%±2.6%. Combined, the results showed that the measurement system was capable of collecting high-density data with constant spatial resolution in orchards, and the canopy projection correction method can effectively correct the distortion in canopy maps caused by both imperfect sun zenith and azimuth angles at data collection. Light interception of individual tree canopies and the variation between/within canopies could be extracted from the corrected canopy maps, which should be useful for the advanced orchard management.

Performance of turmeric in cashew plantation as intercrop compared to sole cropping

HIND AGRICULTURAL RESEARCH AND TRAINING INSTITUTE ABSTRACT : A field investigation was undertaken during 2011-12 to assess the performance of turmeric under cashew plantation as intercrop compared to sole cropping in open area. An experiment was laid out in cashew plantation spaced at 6 m × 6 m by utilizing of 16 m (4 m × 4 m) area and replicated thrice with similar management under both management conditions. Significantly higher fresh weight of rhizome (353.52 g/clump), number secondary rhizome (27.97) and clump size (201.24 cm) of turmeric var. PTS24 was recorded under sole cropping compared to intercropping (271.83 g/clump, 25.53 and 157.88 cm, respectively) under cashew plantation. Interception of PAR (Photosynthetically Active Radiation) by turmeric crop at 150 days after planting as intercrop in cashew plantation was 27390 Lux compared to 30876 Lux in open condition. Due to shade loving nature of turmeric plants growth was significantly higher under cashew intercropping and yield was recorded higher under open situation.

Radiation pattern and radiation balance study over Brassica campestris var. yellow sarson in Gangetic West Bengal

Field experiments were conducted in the experimental farm of Bidhan Chandra Krishi Viswavidyalaya, Kalyani, Nadia, West Bengal (22o57 N, 88o20 E) during Rabi season of three years (2007-08 to 2009-10). The popular variety of the region B-9 was selected and the biomass, grain yield, leaf area index (LAI), crop height and extinction coefficient were measured for each year. The diurnal variations of net radiation (Rn), global solar radiation (GSR) and incident photosynthetically active radiation (PAR0) for different crop growth periods were studied. All the three radiation parameters showed a peak at 11.00 to 12.00 hours on an average and diurnal pattern was almost similar. The seasonal variation did not show any definite pattern. In 2009-10, the LE, G and S values were lower due to lesser amount of Rn throughout the season. In all the years no negative value of S was observed indicating that only upward movement of sensible heat flux occurred. The relationship between intercepted photosynthetically active radiation (IPAR) and biomass were also worked out. There is an immense scope of using the radiation pattern and its balance as inputs of crop growth and yield prediction model.

Light spatial distribution in the canopy and crop development in cotton.

The partitioning of light is very difficult to assess, especially in discontinuous or irregular canopies. The aim of the present study was to analyze the spatial distribution of photosynthetically active radiation (PAR) in a heterogeneous cotton canopy based on a geo-statistical sampling method. Field experiments were conducted in 2011 and 2012 in Anyang, Henan, China. Field plots were arranged in a randomized block design with the main plot factor representing the plant density. There were 3 replications and 6 densities used in every replicate. The six plant density treatments were 15,000, 33,000, 51,000, 69,000, 87,000 and 105,000 plants ha−1. The following results were observed: 1) transmission within the canopy decreased with increasing density and significantly decreased from the top to the bottom of the canopy, but the greatest decreases were observed in the middle layers of the canopy on the vertical axis and closing to the rows along the horizontal axis; 2) the transmitted PAR (TPAR) of 6 different cotton populations decreased slowly and then increased slightly as the leaves matured, the TPAR values were approximately 52.6–84.9% (2011) and 42.7–78.8% (2012) during the early cotton developmental stage, and were 33.9–60.0% (2011) and 34.5–61.8% (2012) during the flowering stage; 3) the Leaf area index (LAI) was highly significant exponentially correlated (R2 = 0.90 in 2011, R2 = 0.91 in 2012) with the intercepted PAR (IPAR) within the canopy; 4) and a highly significant linear correlation (R2 = 0.92 in 2011, R2 = 0.96 in 2012) was observed between the accumulated IPAR and the biomass. Our findings will aid researchers to improve radiation-use efficiency by optimizing the ideotype for cotton canopy architecture based on light spatial distribution characteristics.

The Effects of Maize Planting Density and Weeding Regimes on Light and Water Use

Light and water are among essential resources required for production of photosynthates in plants. A study on the effects of weeding regimes and maize planting density on light and water use was conducted during the 2001/2 short and 2002 long rain seasons at Muguga in - the central highlands of Kenya. Weeding regimes were: weed free (W1), weedy (W2), herbicide (W3) and hand weeding twice (W4). Maize planting densities were 9 (D1) and 18 plants m -2 (D2) intercropped with Phaseolus vulgaris (beans). The experiment was laid as randomized complete block design replicated four times and repeated twice. All plots were thinned to 4 plants m -2 at tasseling stage (96 DAE) and thinnings quantified as forage. Soil moisture content (SMC), photosynthetically active radiation (PAR) interception, evapo-transpiration (ET crop), water use efficiency (WUE), and harvest index (HI), were determined. Percent PAR was higher in D2 than in D1 before thinning but higher in D1 than in D2 after thinning in both seasons. PAR interception was highest in W2 but similar in W1, W3 and W4 in both seasons. SMC was significantly lower in W2 but similar in W1, W3 and W4. D2 had lower SMC than D1 in season two. Weeding regime significantly influenced ET crop, while planting density and weeding regime significantly influenced WUE and HI. D2 maximizes water and light use for forage production but results to increased intra-specific plant competition for water and light severely before thinning (96 DAE) that reduce grain yield in dual purpose maize, relative to D1.

Effect of cropping system on radiation use efficiency in double-cropped wheat–cotton

Wheat–cotton double cropping is the leading cropping system in the Yellow River Valley and the Yangtze River Valley in China. To comprehend the effects of cropping systems on the radiation use efficiency (RUE) in wheat–cotton double cropping, field experiments involved four cropping systems, namely monoculture cotton (MC), wheat/intercropped cotton (W/IC), wheat/transplanted cotton (W/TC) and wheat/direct-seeded cotton (W/DC) and two cotton cultivars were conducted in 2011/2012 and 2012/2013. The results showed that wheat–cotton double cropping improved radiation use by increasing the intercepted photosynthetically active radiation and RUE compared with monoculture cotton. Averaged over two years, the RUE of monoculture cotton was 1.20gDMMJ−1 for Siza 3 and 1.14gDMMJ−1 for CCRI 50, while that of double cropped cotton was 1.19–1.93gDMMJ−1 higher than monoculture cotton, with the RUE of cotton in W/DC was the highest, followed by in W/TC and W/IC. The analysis of cropping systems effects on cotton canopy structure and light distribution indicated that the high RUE was associated with the favorable intra-canopy light distribution. Cotton in W/IC, W/TC and W/DC system intercepted 87.1%, 54.6% and 44.3% as much PAR as the monoculture cotton for Siza 3 and 86.9%, 59.3% and 46.2% as much PAR as the monoculture cotton for CCRI 50, respectively. Double cropping cotton intercepted significantly lower PAR than monoculture cotton, which is the result of the lower fPAR caused by initiation shading for IC, later planting for TC and delayed sowing for DC, respectively. Our results suggest that the key factor that limits cotton production in double cropping systems is their lower PAR interception rather than the RUE. Suggestions for further increasing the productivity of radiation should be based on improved capture of radiation by cotton in wheat–cotton double cropping systems. The early maturity cultivar might be more appropriate to double cropping sequential systems.

Radiation Use Efficiency: Evaluation of Cropping and Management Systems

Capture of solar radiation by plant canopies and conversion of this energy into biomass or grain has been described as radiation use efficiency. Radiation use efficiency (RUE) has been developed as a function of biomass accumulation and intercepted photosynthetically active radiation (IPAR) by the canopy and evaluated under conditions not limiting to plant growth. This study was designed to evaluate RUE across a number of corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] experiments in central Iowa with various tillage and management inputs to determine how RUE changed as a function of agronomic management. In these studies, IPAR was derived through the use of a normalized difference vegetation index, which is a surrogate for the photosynthetically active radiation canopy interception term, and total canopy biomass was measured at five times during the growing season from the early vegetative stage through maturity. Grain yields were obtained from each plot with both hand‐ harvested and combine samples. Values for RUE showed a linear relationship between biomass and IPAR for the entire growing season, with the better fit when the relationship was confined to the vegetative development period. There were differences among years, with management and tillage systems affecting RUE values through the differences in biomass or grain yield. Grain yield relationships to IPAR showed more variation than total biomass, with yearly differences evident in the amount of IPAR during the grain‐filling period suggesting that the length of the grain‐filling period is a dominant factor in grain yield. Application of RUE to field‐scale observations will provide a method of assessing where crop productivity is limited.

Agronomic Response of Soybean Varieties to Plant Population in the Guinea Savannas of Nigeria

The agronomic responses of three contrasting soybean [Glycine max (L.) Merr.] varieties to plant populations were examined in two distinct agro‐ecological locations (at Samaru Zaria and Samaru‐Kataf), both in the Guinea savanna of northern Nigeria in 2009, 2010, and in 2011 growing seasons. Three soybean varieties: TGx1835‐10E, TGx1904‐6F, and TGx1448‐2E differing in maturity duration (early, medium, and late maturing, respectively), were evaluated at four plant populations (266,700, 333,300, 533,300, and 666,700 plants ha−1) using a split plot arrangement in randomized complete block design with three replications. The plant populations were the main plots, whereas varieties were subplots. The proportion of intercepted photosynthetically active radiation (IPAR) and leaf area index (LAI) increased with increasing plant population at both locations, indicating that high leaf area indices and high degree of canopy closure at higher plant population intercepted more light than the canopy at lower population and subsequently resulted in relatively high grain and fodder yields. At both locations, optimum plant populations ranged from 533,300 to 666,700 plants ha−1 across the years. The northern Guinea savanna location (Samaru Zaria) produced more pods m−2, grain yield, and fodder at higher plant populations than that at the southern Guinea savanna (Samaru‐Kataf). Varieties TGx1448‐2E and TGx1904‐6F intercepted higher proportion of IPAR had higher LAI and produced a greater number of pods m−2, seeds m−2, grain yield, and fodder than TGx1835‐10E at both locations in years of good rainfall. These data suggest that soybean yields in the Guinea savanna of northern Nigeria can be increased using higher plant populations than those currently recommended.

Effect of Seed Distribution and Population on Maize (Zea maysL.) Grain Yield

Maize planting is normally accomplished by hand in the developing world where two or more seeds are placed per hill with a heterogeneous plant spacing and density. To understand the interaction between seed distribution and distance between hills, experiments were established in 2012 and 2013 at Lake Carl Blackwell (LCB) and Efaw Agronomy Research Stations, near Stillwater, OK. A randomized complete block design was used with three replications and 9 treatments and a factorial treatment structure of 1, 2, and 3 seeds per hill using interrow spacing of 0.16, 0.32, and 0.48 m. Data for normalized difference vegetation index (NDVI), intercepted photosynthetically active radiation (IPAR), grain yield, and grain N uptake were collected. Results showed that, on average, NDVI and IPAR increased with number of seeds per hill and decreased with increasing plant spacing. In three of four site-years, planting 1 or 2 seeds per hill, 0.16 m apart, increased grain yield and N uptake. Over sites, planting 1 seed, every 0.16 m, increased yields by an average of 1.15 Mg ha−1(range: 0.33 to 2.46 Mg ha−1) when compared to the farmer practice of placing 2 to 3 seeds per hill, every 0.48 m.

Effects of planting density and cultural intensity on stand and crown attributes of mid-rotation loblolly pine plantations

Loblolly pine (Pinus taeda) is an important timber species in the southeastern US and abroad. A better understanding of loblolly pine crown relationships with growth has implications for improving productivity estimates using process-based models or remote sensing techniques. Four study installations in the Upper Coastal Plain and Piedmont of Georgia were used to examine the effects of planting density and cultural intensity on loblolly pine stand growth and crown attributes. Treatments included six planting densities, ranging from 740 to 4440 trees ha−1, in a split-plot design with two different levels of fertilization and competition control. The “low intensity (LI)” cultural treatment included relatively high nutrient inputs and early competition control. The “high intensity (HI)” cultural treatment included even greater nutrient inputs and complete sustained competition control. Treatment effects on stand and crown attributes were examined at age 13. Fertilization and competition control did not have a major influence on stand and crown attributes. Stands planted at lower densities resulted in significantly greater DBH and height but less standing volume per hectare, basal area per hectare, and current annual increment (CAI) volume growth compared to stands planted at higher densities. Stand-level foliar biomass, peak projected leaf area index (LAI), foliar nitrogen (N) content, specific leaf area (SLA), and intercepted photosynthetically active radiation (IPAR) were significantly greater for stands planted at higher densities, while live crown length and crown ratio were significantly greater for stands planted at the lower densities. IPAR efficiency (CAI per IPAR) was significantly affected by planting density, with values of 0.32–0.42m3 %IPAR−1 for 740 and 4440 trees ha−1, respectively. At this stage of stand development, light limitations due to high stocking have a greater influence on growth than soil resource limitations for the loblolly pine plantations analyzed in this study. Higher density stands resulted in increased SLA and IPAR efficiency, supporting the idea that higher density stands utilize light more efficiently than lower density stands.

Comparison of different BRDF correction methods to generate daily normalized MODIS 250 m time series

Realizing the full benefits of MODIS' temporal resolution requires, among others, the correction of the directional effect (i.e. the combined impact of the variation of the measurement geometry and of the observed land surface upon the registered radiant flux). While different BRDF methods have been proposed to address this effect, its performance has been evaluated at coarse spatial resolutions making it difficult to assess its applicability to, for example, crop monitoring. Here we test 2 approaches based on two different assumptions: the Classic approach that relies on the hypothesis of stable target and a recent Alternative that is based on the idea that despite reflectance magnitude may change rapidly, the BRDF shape varies slowly in time. Additionally, we segmented the growing season into different numbers of periods for the BRDF correction (a single period along the growing season, 3 periods based in phenology and 9–12 periods of fixed 16-days). The resulting 6 methods were compared over annual crops (wheat, maize and soybean) at 250m spatial resolution from a site located in the Argentine Pampas. We used MOD and MYD 09 GQ and GA as inputs and compared the corrected daily red and infrared reflectances and the NDVI time series against the filtered benchmark (input time series with quality filters applied) by means of the high frequency variability (i.e. noise). We also tested whether corrected time series were better correlated with soybean PAR interception and biomass. Our results showed that methods' performance was more explained by the number of periods than by the approach (Classic or Alternative). Single period methods decreased noise by 52%, 55% and 4% for red, infrared and NDVI time series. The use of 3 periods improved the correction performance to 63, 64 and 24% for red, infrared and NVDI time series respectively, while the highest reductions (65, 68 and 32% for red, infrared and NVDI) were found with 16-day intervals (9–12 periods) considering a magnitude inversion process. Wheat displayed the lowest noise reduction compared to the other crops. BRDF parameters obtained from different methods were associated to crop structure, suggesting that they have biophysical meaning. The decrease in noise obtained with correction methods was translated into a better assessment of the fraction of intercepted PAR and biomass. These promising results suggest the possibility of extensive field crop monitoring at an unprecedented temporal resolution.