Jacob Amir

A model to assess nitrogen limitations on the growth and yield of spring wheat

Under many conditions the availability of soil nitrogen imposes an important constraint on wheat (Triticum aestivum L.) yields. In this paper a simple, mechanistic model of spring-wheat growth and yield was proposed to account for nitrogen uptake and use by the crop. A soil nitrogen balance was developed so that crop nitrogen uptake was restrained when the available mineral nitrogen in the soil was exhausted. The crop nitrogen uptake rate was calculated as a function of cumulative thermal units. Leaf area development and maintenance, radiation-use efficiency, and stem growth were assumed to depend on accumulated nitrogen. Seed growth resulted in nitrogen transfer from leaves and stems to the seeds. The model was compared against data collected in nine years of experimentation at Gilat, Israel. Good agreement between observed and simulated yields was obtained for varying nitrogen fertilizer treatments (r2=0.94) and levels of soil nitrogen following fallow (r2=0.93).

A model of water limitation on spring wheat growth and yield

Abstract A simple, mechanistic model describing the growth and yield of spring wheat ( Triticum aestivum L.) was extended to water-limited conditions. The activities of three physiological processes were potentially retarded upon soil dehydration: leaf growth, crop gas exchange, and rate of ontogenetic development. Each of these processes was related directly to soil water content, which was calculated daily based on estimates of transpiration, soil evaporation, and water additions. For eight of the nine years experimentally studied at Gilat, Israel, the agreement between simulated and observed grain-yields differed no more than 26 g m −2 . In the ninth year (1979/80), a severe drought during seed maturation decreased yields and caused the simulation to overestimate the yield. Nevertheless, the simple, mechanistic model demonstrated the importance of water availability in accounting for seasonal variations in yield. Both the amount and pattern of seasonal rainfall were found to be important in determining yield. Drought stress at anthesis was found in the simulations to have a particularly large negative effect on grain-yield, because anthesis coincides with the period in crop development requiring the maximum amounts of water.

A model of the temperature and solar-radiation effects on spring wheat growth and yield

A simple mechanistic model was developed to analyze the effects of temperature and solar radiation on spring wheat (Triticum aestivum L.). This model uses relatively few, conservative relationships to define leaf-area development as a function of temperature, biomass accumulation as a function of intercepted radiation, and seed growth as calculated from a linear increase in harvest index with time. Using daily weather observations of solar radiation, minimum temperature, and maximum temperature over a 10-year period at Gilat, Israel, a comparison of yields between model simulations and field observations was made. The simulations highlighted the influence of temperature on the development of crop leaf area, accumulated biomass, and grain-yields. Temperature especially influenced the duration of ontogenetic events, with cool temperature being clearly advantageous for increasing environmental yield potential of wheat. For unstressed wheat crops, the simple, mechanistic model accounted for much of the variability in grain-yield among seasons.

Wheat production in an arid environment. 1. Water-use efficiency, as affected by management practices

The objective of this study was to evaluate management practices which may improve the water use efficiency (wue) of spring wheat (Triticum aestivum L.) in an arid Mediterranean-type environment. Multifactorial experiments were performed for ten years at Gilat in the Negev Desert of Israel, where the average annual rainfall was 231 ± 70 mm, all of which fell during the growing season (December to April), and an average growing-season Class-A pan evaporation of 504 ± 62 mm. Basic management treatments were: (1) continuous wheat, disk-tillage (CD); (2) continuous wheat, plowing-tillage (CP); (3) wheat after fallow, disking as preparative tillage (FD); and (4) wheat after fallow, plowing as preparative tillage (FP). Three additional continuous wheat disk-tillage treatments were examined for chemical control of soil pathogens and weed-control treatments. The experiment also included four nitrogen-level treatments (0, 5, 10, and 15 g N m−2) and two water regimes, one rainfed and the other fully irrigated. In both contrasting water regimes, grain-yield was not significantly influenced by preparative tillage treatments. Profitable grain yields (> 100 g m−2) and profitable response to nitrogen (> 4 g grain per g N added) were obtained with continuous wheat management in only five out of ten years, when the rainfall was above 250 mm. A highly significant increase in yield and wue for grain production, compared with CD management, was obtained for the same N and water regime, with the wheat-after-fallow management practice (FD). Profitable grain-yield was obtained with wheat-after-fallow management in nine out of ten years. In eight out of the ten years there was no plant-available stored soil water at sowing in FD management, and therefore the significant increase in wue for the ‘dry’ fallow treatment could not be ascribed to stored water. Water-use efficiency and productivity were similarly increased in the CD management by a broad-spectrum biocide applied to the soil, suggesting that yield increase after ‘dry’ fallow is through soil sanitation improvement. The significant increase in grain production in wheat after ‘dry’ fallow management resulted from a marked elevation in the transpiration/evapotranspiration ratio, due to a significant enhancement in root-length density. In rainy years when water supply increased above 250 mm, the advantage of the wheat after ‘dry’ fallow management disappeared. It is concluded that, under arid conditions, improvement of the root density by chemical, cultural or breeding techniques is a feasible strategy for counteracting limited water supply.

Respiration, ATP level, and sugar accumulation in potato tubers during storage at 4°

Abstract A kinetic study was made of the relationship between respiration rate, sugar content and ATP levels, in fresh and aged potato tubers stored at 4°. The ATP content in tubers rose rapidly immediately after the chilling stress, while respiration rate decreased below the initial rate and sugar accumulation was not detected. After 4 days of storage, the ATP level declined and the sugars started to accumulate. The typical increase in respiration rate that usually follows chilling stress, appeared only in fresh tubers (at about the 6th day of storage). In dinitrophenol-treated tubers, the ATP level remained below the initial level and sugar accumulation was blocked completely. The evidence presented suggests that ATP elevation is not generated by the respiration burst.

A straw mulch system to allow continuous wheat production in an arid climate

Abstract Cereal Cyst Nematode (CCN, Heterodera avenae Woll.) has been shown to be a devastating pest for wheat (Triticum aestivum L.) in dryland regions. Fallowing in the season preceding the cropping season has been hypothesized to sanitize the soil of CCN and allow wheat production. This paper explores management options that might allow the continuous production of wheat in these regions. In a 20-year study in the Negev, Israel, on a sandy loam, loessial, soil, it was found that in those seasons with high rainfall there was virtually no decrease in annual wheat yields for continuous crops as compared to biennial fallow yields obtained with the conventional wheat system. The hypothesis that high soil water content substantially alleviates the damage resulting from CCN infestation was confirmed in a pot study. A practical solution for maintaining high soil water content in the field was to leave a straw mulch on the soil surface to decrease soil evaporation. A chopper was added to a grain harvester to finely chop the straw so that it settles to the soil surface through the stubble, and a no-till drill was used for sowing through the straw. The straw-mulch system was shown to result in annual yields from continuous wheat that were equivalent to yields in alternate years with the conventional fallow wheat system, thereby doubling wheat production in this dryland region.

Cereal cyst nematode effects on wheat water use, and on root and shoot growth

Abstract Wheat ( Triticum aestivum L.) is grown in many arid regions using fallow management whereby no crop is grown in alternate cropping seasons. Although fallowing is important in increasing the availability of water and nitrogen to crops in many environments, experiments in Israel revealed that water carryover from the fallow season for wheat production was rare. This paper examines the possibility that improved water use, and improved root and shoot growth, result from soil sanitation of cereal cyst nematode (CCN, Heterodera avenae Woll.) in the fallow season. Pot experiments in controlled environments revealed a dramatic, negative effect of various populations of CCN on wheat root growth. The decrease in root growth was associated with decreased shoot growth and decreased rates of transpiration. Mechanical pruning of roots mimicked the effects of CCN infestation indicating that root pruning is probably the primary damage of CCN. In the field, dry weight yields of wheat were maintained even in continuous wheat management when a soil biocide was used to control CCN. It is proposed that the success of the fallow management is based on the fact that CCN cysts hatch in wet soil during rainy periods of the fallow year but fail to produce a new generation of cysts because no host plants are present.

Wheat production in an arid environment. 2. Role of soil pathogens

In the Negev Desert agro-system, wheat (Triticum aestivum L.) yields under fallow management practices have been shown to be 84% greater than those from continuous wheat. The higher yields for the fallow management were achieved without improved soil water storage, and soil nitrogen was not a limiting factor in either system. Yields were similarly increased after several years in continuous wheat, by chemical control of soil pathogens. The objective of this study was to identify the dominant soil pathogens in the different management systems and to assess their influence on grain production. A 19-month fallow period or a chemical soil treatment significantly reduced the population of two dominant nematodes, Pratylenchus mediterranea and Heterodera avenae. The nematicide aldicarb, which was used to differentiate between fungicidal and nematicidal effects of the broad-spectrum biocide metham-sodium, increased wheat yield significantly in one out of four years at Gilat, and in two out of four years at Magen. These results emphasize that, although the parasitic nematodes reduced yields in some years, no clear and consistent correlation between nematode population and grain-yield could be shown. The root-rot fungus Cochliobolus sativus was the dominant fungal pathogen in the soil, but frequency of recovery of the fungus from sub-crown internodes was not related to yield differences between management systems. Under irrigation, the pathogen Gaeumannomyces graminis var. tritici (the cause of take-all) became dominant, and greatly reduced grain-yields. When the disease was controlled either chemically or biologically, yields returned to the level prior to disease onset. No symptom of take-all was found in the same years and treatments under dryland conditions. It is concluded that the high yields achieved with the fallow wheat management are a result of improved soil sanitation, which justifies an effort in developing pest and disease-tolerant/resistant cereal varieties for continuous wheat cropping systems.

Model analysis of a straw mulch system for continuous wheat in an arid climate

Abstract Wheat ( Triticum aestivum L.) production in some dryland regions is severely limited by the cereal cyst nematode ( Heterodera avenae Woll.). Conventional fallow management during a wet period has been shown to allow hatching of the cysts during the fallow season and thereby sanitize the soil for the subsequent wheat crop. Recently a straw mulch (SM) management has been introduced into a long-term experiment in the Negev region of Israel. This management ameliorated the nematode damage and allowed continuous wheat production. Only three seasons of successful experimentation exist with the SM system so questions remain about its performance over seasons with differing weather conditions. A simple, mechanistic, wheat model was extended to simulate wheat development and growth when the crop is grown on nematode-infested soils. Incorporating statements describing inhibition of rooting depth as a result of nematode activity resulted in good agreement between simulations and 16 seasons of yield observations on continuous wheat. The effect of SM was simulated simply by decreasing soil evaporation and this resulted in higher levels of soil water and decreased nematode inhibition of rooting. Good agreement was obtained between the three seasons of experimental data and simulations of the SM system, with predicted grain yield within 10% of observations. Over 16 seasons, simulations of the SM system indicated substantial grain yield increases over continuous wheat in all but the highest-yielding season. Simulations in 14 seasons with conventional fallow management revealed that annual yields of SM were equivalent to biennial yields of the fallow system, resulting in a predicted doubling of wheat production for this dryland region of the Negev.

Sugar accumulation in chemically debudded potato tubers during cold storage

Abstract Potato tuber buds may be excised by immersion of the tubers in a mixture of EtOH-Me 2 CO (1:1) for 4 hr. This enabled the study of the effect of tuber aging (at 17°) on the starch-to-sugar conversion during storage at 4°, in the absence of complications due to sprouting. Sugar accumulation during a two-week period of storage at 4° decreased with increasing time of prior storage at 17°.