The estimation of ground cover of potato by reflectance measurements

Summary In nine field trials, the proportion of ground covered by potato canopy was estimated using near-infrared and visible reflectance measurements. The data set spanned a range of cultivars, treatments, soil types, soil moisture regimes and growing conditions that ranged from severely stressed to near-potential growth. Near-infrared reflectance of the canopy, corrected for soil reflectance (WDVI), was related to ground cover estimated by a trained expert with or without the use of a grid-frame. Different linear regressions between ground cover and WDVI for the early phase of growth and for the late phase, allowed the calculation of ground cover of potato from WDVI with anabsolute accuracy of 3.5–6.5%. The derived regression lines are expected to have a general applicability for potato grown on soils of temperate regions. It is concluded that reflectance measurement is an objective, fast and reliable method for estimating the proportion of ground covered by potato canopies.     

Disentangling the effect of environmental factors on yield and nitrogen uptake of irrigated rice in Asia

Rice yield is the result of the interaction between genotype (cultivar characteristics), environment (climate and soil conditions), and management. Few studies have attempted to isolate the contribution of each of these factors. Here the rice growth model ORYZA2000 was used to analyse the variation in yield, nitrogen (N) uptake, and internal N use efficiency (INUE, grain yield per unit total crop N uptake) of rice in different environments. First, ORYZA2000 was calibrated and evaluated using an empirical data set that spanned three varieties, three years, and eight locations in Asia. Next, we used the model to investigate the relative contribution of indigenous soil N and external N supply and of the weather factors temperature and radiation to observed variation in yield.     

Subcutaneous tissue discoloration in ware potatoes. 1. A chain analysis in the Netherlands

Summary In the chain of handling operations from harvesting to packaging inclusive, potatoes are exposed to many brief mechanical forces (impacts) and to long-term pressure. Impact and pressure can lead to subcutaneous tissue discoloration causing qualitative and quantitative losses. We investigated the characteristics of construction and utilization of representative Dutch ware potato handling chains and found that the number and height of drops appeared to be too high, the use of cushioning materials insufficient and the speed of the transporting parts too high and not in balance with each other. The contribution to the total amount of subcutaneous tissue discoloration was 16% for the harvesting to bin filling phases inclusive, 22% for the storage phase, 27% for the shovelling to truck loading phases inclusive and 35% for the truck unloading to packaging phases inclusive. These contributions varied considerably within phases and within links. The results can be used to develop equipment, upgrade present chains and design new, produce-frendly handling chains.     

Yield and water productivity of rice–wheat on raised beds at New Delhi, India

Permanent raised beds are being proposed for the rice–wheat system in the Indo-Gangetic Plain to increase its productivity and to save water. It is not clear whether reported water savings in rice arise from the geometry of the beds per se or from the particular water management that keeps the soil in aerobic conditions and that can also be applied on flat land. Moreover, little research has been reported on direct seeding of rice on raised beds and on the effect of raised beds on the subsequent wheat crop. In this paper we compare the yield, input water (rainfall and irrigation) use and water productivity of dry-seeded rice on raised beds and flat land with that of flooded transplanted and wet-seeded rice, and analyze the effects of beds on the subsequent wheat crop. The experiment was conducted in 2001–2003 at New Delhi, India.

Rice yields on raised beds that were kept around field capacity were 32–42% lower than under flooded transplanted conditions and 21% lower than under flooded wet-seeded conditions. Water inputs were reduced by 32–42% compared with flooded rice, but could also be accomplished with dry seeding on flat land with the same water management. Reduced water inputs and yield reductions balanced each other so that water productivity was comparable among most treatments. Wheat yield was 12–17% lower on raised beds than on flat land with conventional (20 cm) row spacing. Neither wheat nor rice on raised beds compensated for the loss in rows by extra tillering or leaf growth at the edges of the rows. There was no carry-over effect of type of land preparation in rice on the growth and yield of the subsequent wheat crop. Further research on raised beds should focus on the selection of suitable rice and wheat varieties, soil health issues such as nematodes and micro-nutrient deficiencies, weed control, bed stability and long-term carry-over effects from one crop to the other.     

Yield formation and tillering dynamics of direct-seeded rice in flooded and nonflooded soils in the Huai River Basin of China

Water shortage in the Huai River Basin prompts farmers to adopt water-saving technologies such as direct-seeded nonflooded or aerobic rice. Different cultivation practices impact on tiller growth and development. Improved insight into tiller dynamics is needed to increase yield in these production systems. We conducted field experiments with four direct-seeded rice varieties under flooded and nonflooded conditions in Mengcheng county, Anhui province, in 2005–2006. The soil water content in the nonflooded treatment varied between saturation and field capacity. Yields in nonflooded soil ranged from 3.6 to 4.7 t ha⁻¹, and did not differ significantly from yields in flooded soil that ranged from 3.6 to 5.1 t ha⁻¹. Variety had a significant effect on biomass, yield, panicle number, spikelet number, grain weight, and grain filling percentage. Panicle number was the main factor limiting yield, resulting from a low tiller emergence frequency and a low fraction of productive tillers in both the flooded and the nonflooded soils. On average, the panicle number was 159–232 m⁻², including 34–167 productive tillers per m² for all the varieties under the two water regimes. The contribution of productive tillers to yield varied between 7% and 47%. There were two peaks of tillers that contributed to yield, one at the low (4th or 5th) and one at the high (10th or 11th) phytomer orders. Frequencies of tiller emergence at most phytomer orders were higher in the flooded soil than in the nonflooded soil. There were no significant differences in frequencies of productive tiller emergence and contributions to yield from tillers between the soil water regimes for three of the four tested varieties. To increase yield in direct-seeded nonflooded rice production systems, both the tiller emergence frequency and the fraction of productive tillers should increase through breeding, improved crop management, or a combination.     

Oceanographic basis of the global surface distribution of Prochlorococcus ecotypes

By using data collected during a continuous circumnavigation of the Southern Hemisphere, we observed clear patterns in the population-genetic structure of Prochlorococcus, the most abundant photosynthetic organism on Earth, between and within the three Southern Subtropical Gyres. The same mechanisms that were previously invoked to account for the vertical distribution of ecotypes at local scales accounted for the global (horizontal) patterns we observed. Basin-scale and seasonal variations in the structure and strength of vertical stratification provide a basis for understanding large-scale horizontal distribution in genetic and physiological traits of Prochlorococcus, and perhaps of marine microbial communities in general.     

Effect of haulm destruction supplemented by cutting off roots on the incidence of black scurf and skin damage,flexibility of harvest period and yield of seed potatoes in field experiments

In field experiments, supplementing chemical haulm destruction (CHD) with cutting off roots resulted in a lower incidence of black scurf and skin damage (ripping off the skin) at harvest date than CHD alone. The lower susceptibility to skin damage at harvest allowed harvesting to beging on an earlier date, when only a few sclerotia ofRhizoctonia solani had developed. Furthermore, black scurf often developed more slowly after haulm destruction if roots had been severed and this enabled harvesting to be postponed.At harvest, gross yield was highest if roots had not been cut through prior to CHD: the extra weight existed merely of water. Weight loss during storage, however, as well as grading losses resulting from black scurf were greater after CHD alone. This resulted in an equal or even lower net yield after CHD alone than after CHD supplemented by root severing. The favourable effects of supplementing CHD with cutting off roots almost equaled those of the mechanical removal, often called haulm pulling or plant pulling. Factors that may affect the development of black scurf are discussed.Samenvatting Pootaardappelen raakten minder bezet met lakschurft en werden minder ontveld bij de oogst na looftrekken of na wortelsnijden plus doodspuiten dan na loofklappen plus spuiten. Al vanaf de derde dag na trekken of wortelsnijden plus doodspuiten was de mate van ontvelling zo gering, dat met het oogsten kon worden begonnen. Op zo'n vroeg tijdstip na loofdoding konden knollen worden geoogst met nog weinig lakschurft, want de stimulering van lakschurft werd pas zichtbaar vanaf 7 à 10 dagen na loofdoding. Lakschurft ontwikkelde zich het traagst na looftrekken. Ook wortelsnijden bij het doodspuiten gaf meestal een tragere ontwikkeling van lakschurft dan klappen plus spuiten. Daardoor konden na wortelsnijden plus doodspuiten en vooral na looftrekken op nog latere tijdstippen knollen met weinig lakschurft worden geoogst.Na klappen plus spuiten was het bruto gewicht bij de oogst het hoogst. Dat meergewicht bleek louter uit water te bestaan en het verloop in knolvochtgehalte leek erop te wijzen dat de wortels nog gedurende een week na doodspuiten blijven functioneren. Dat gaf wel knollen met een hoger vochtgehalte die meer ontvelden en meer vocht en dus gewicht verloren. Dit groter gewichtsverlies bij bewaren en de hogere leesverliezen door lakschurft deden de meeropbrengst teniet: zo werd het netto knolgewicht na klappen plus spuiten, al naar gelang het moment van oogsten, meestal gelijk aan, of lager dan het netto knolgewicht na het trekken of na wortelsnijden plus doospuiten. In dit artikel worden de factoren besproken, die mogelijk van invloed zijn op de ontwikkeling van lakschurft.     

Possible causes of yield failure in tropical aerobic rice

Aerobic rice is a water-saving rice production system for water-short environments with favorable soils and adapted, potentially high-yielding varieties that are direct dry seeded. Soils remain aerobic but supplementary irrigation is applied as necessary. In the dry season of 2004 and 2005, a water by N experiment was set up at the location “Dapdap” in central Central Luzon, Philippines, to explore water and N management strategies in aerobic rice. The experiment was laid out as a split-plot design on a loamy sand soil with three water treatments (irrigation twice per week, once per week, and once in two weeks with modifications) and 5 N levels (0–200 kg ha⁻¹). Average seasonal soil moisture tension ranged from 9.2 to 20 kPa but yield hardly responded to the treatment combinations and ranged from 0 to 2 t ha⁻¹. In addition to trial-specific parameters, root knot nematodes and micronutrients (2005) were monitored. Galling of roots due to nematodes was assessed through a rating scale of 0–5, with 0 = no galling and 5 = >75% of the root system galled. The degree of galling reached a level of 5 at flowering and harvest in 2004, and 3 at tillering and 4 at harvest in 2005. Results of a plant tissue analysis at mid-tillering for Fe, Mn, and Zn showed on average values above critical levels; individual replicates, however, indicated deficiencies for Mn. In addition to actual field observations, we used simulation modeling (ORYZA2000) as a tool to estimate attainable yield under actual water conditions and N inputs to explore how yield failure set in. Simulation results matched observed values for total above-ground biomass and leaf area index quite well when no N was applied. When high rates of N (200 and 165 kg ha⁻¹) were applied, simulated values matched actual field data only until about the panicle initiation stage; afterward, observed values remained below the simulation. We interpreted this as evidence that growth-limiting factors other than water or N affected the crop from this growth stage on. Observations made in the field on root knot nematodes and micronutrients suggested that these two factors, especially root knot nematodes, may have been major constraints to crop development in this experiment.     

Effect of irrigation method and N-fertilizer management on rice yield, water productivity and nutrient-use efficiencies in typical lowland rice conditions in China

Alternate wetting and drying irrigation (AWD) has been reported to save water compared with continuous flooding (CF) in rice cultivation. However, the reported effects on yield varied greatly and detailed agro-hydrological characterization is often lacking so that generalizations are difficult to make. Furthermore, it is not known how AWD modifies nutrient use efficiencies and if it requires different N-fertilizer management compared with CF. This study quantified the agro-hydrological conditions of the commonly practiced AWD and compared the impact of AWD and CF irrigations at different N-fertilizer management regimes on rice growth and yield, water productivity, and fertilizer-use efficiencies in five crop seasons in 1999 and 2000 at two typical lowland rice sites in China (Jinhua, Zheijang Province and Tuanlin, Hubei Province), with shallow groundwater tables.Grain yields varied from 3.2 to 4.5 t ha^–1 with 0 kg N ha^–1 to 5.3–8.9 t ha^–1 with farmers N-rates (150 kg N ha^–1 in Jinhua and 180 in Tuanlin). In both sites, no significant water by nitrogen interaction on grain yields, biomass, water productivity, nutrient uptakes and N-use efficiency were observed. Yield and biomass did not significantly differ (P >0.05) between AWD and CF and among N timings. The productivity of irrigation water in AWD was about 5–35% higher than in CF, but differences were significant (P <0.05) only when the rainfall was low and evaporation was high. Increasing the number of splits to 4–6 times increase the total N uptake, but not total P-uptake, and total K-uptake compared with farmers practices of two splits. Apparent Nitrogen recovery (ANR) increased as the number of splits increased, but there was no significant difference in ANR between AWD and CF. During the drying cycles of AWD irrigation, the perched water table depths seldom went deeper than – 20 cm and the soil in the root zone remained moist most of the time. The results suggest that in typical irrigated lowlands in China, AWD can reduce water input without affecting rice yields and does not require N-fertilizer management differently from continuous flooding. The results can be applied to many other irrigated lowland rice areas in Asia which have a shallow groundwater table.     

Biotic and abiotic causes of yield failure in tropical aerobic rice

Aerobic rice is a new production system for water-short environments. Adapted varieties are usually direct dry seeded and the crop grown under aerobic soil conditions with supplementary irrigation as necessary. Occasionally, yield failures occur which may be related to soil health problems. In the dry season of 2006 and 2007, we conducted a field experiment in the Philippines, to identify the major causes of such yield failure. Four treatments were implemented: (i) Control of direct dry-seeded rice (improved upland variety Apo), (ii) Biocide application, (iii) transplanting into aerobic soil, and (iv) 1 year fallow. Yield in the Biocide treatment was 2 t ha⁻¹ in both years. In all other treatments, yield was 0–0.3 t ha⁻¹. Plants grown in the Biocide treatment showed a reduced degree of galling of roots caused by root-knot nematodes (RKN) and better general root health than the Control treatment. Potentially pathogenic fungi were isolated from root samples (Pythium sp., Fusarium sp., and a Rhizoctonia-like species). Abiotic effects of the Biocide treatment were an increase in KCl-extractable N (initial season 2007) and a decrease in initial soil pH. In the Control treatment, soil pH increased from 6.5 to 8.0 over the two seasons. In 2007, plant tissue analysis indicated Mn deficiency in the Control treatment. Plants that were subjected to foliar micronutrient sprays reacted positively to Fe and Mn sprays in the Control treatment, and Mn spray in the Biocide treatment. We concluded that the Biocide application led to favorable soil conditions by reducing biotic stresses such as RKN and improving nutrient availability. In the other treatments, an interaction of RKN and micronutrient deficiencies with increasing soil pH led to yield failure.