Modelling interactions in grass-clover mixtures

The study described in this thesis focuses on a quantitative understanding of the complex interactions in binary mixtures of perennial ryegrass (Lolium perenne L.) and white clover (Trifolium repens L.) under cutting. The first part of the study describes the dynamics of growth, production and the structural characteristics of contrasting grass and clover cultivars under field conditions. This basic information is used in the second part to quantify light absorption, C0 2 assimilation, radiation use efficiency (RUE) and light competition of the species using a modelling approach.Both species showed a seasonal pattern in growth of the dry matter (DM) and leaf area index (LAI) during the season so that the grass-dominated swards during spring shifted to clover dominance in summer. Without N fertilisation (-N), this seasonality was mainly controlled by the weather conditions. However, in fertilised mixtures (+N) grass was the dominant component of the mixture during the whole season and clover growth was always limited by light. The competitive ability and persistence of clover were determined by the structural characteristics of the cultivars. In the -N swards, both large and small-leaved clover cultivars had a higher proportion of their leaf area at the top canopy layers than their companion grass. In the +N mixtures, this was observed only in largeleaved clover, whereas the small-leaved cultivar was strongly overtopped. The difference between cultivars; was mainly due to the pattern of allocation of the DM into the supporting tissues.Experimental results showed two sources of vertical heterogeneity within the mixed grass-clover canopies: different patterns of LAI distribution and leaf dispersion. The validity of the canopy light partitioning model was considerably improved by introducing these sources of variation into the model. Using this model the RUE of species was calculated for different regrowth periods. Grass and clover had a different RUE in mixture and monoculture, but overall RUE was higher in grass, particularly in spring. The variation in the DM yield of grass under different treatments was due to changes in RUE and absorbed radiation. However, in clover these differences were mainly due to the amount of absorbed radiation. Quantification of light competition showed that in spring grass was the strongest competitor. In summer, the competitive ability of clover was related to N level and clover cultivar. Without N, both large and small-leaved clover were better competitors than grass. However, in the +N swards only the large-leaved clover had the same competitive ability as its companion grass. In both species a leaf N profile developed during regrowth, parallel to the light profile within the canopy. The effect of the observed compared to a uniform leaf N profile on canopy C02 assimilation of species was low, but it was different between mixtures and monocultures. It was concluded that the effect of canopy structure on productivity of species was more important than their assimilatory characteristics. The persistence of white clover under cutting may be improved by choosing cultivars with a higher competitive ability, based on canopy structure

Agroecological Zoning of Wheat in Khorasan ProvinceRisk Analysis

Abstract\ud In crop zonation studies potential yield is usually estimated by simulation models where management inputs are defined as recommended by research stations. However, these recommendations are not necessarily in accord with the local situation. Therefore, the prediction of simulation models is subjected to uncertainty or risk. In this research the risk of wheat yield estimation due to management inputs in Khorasan provinces is analysed by application of Monte Carlo simulation. Potential wheat yield was estimated by WOFOST model which was previously validated against the experimental data. The results of sensitivity analysis indicated that change in planting date in order of ±50 days relative to a reference sowing date resulted in a drastic variation in estimated wheat yield. However, potential wheat yield was not sensitive to variation in planting density in the range of ±50% of the reference density. Therefore, risk analysis was performed on planting date. 100 random planting dates were generated using a random data generator software and the WOFOST model was run for each generated date during 10 climatic years (1375-1385). Using the simulation results probability distribution of potential wheat yield was calculated for recommended planting date and dates with ±15 or ±30 days deviation. The results showed that risk of wheat yield in response to change in planting date was different between provinces. In the Northern Khorasan province earlier planting by 15 days compared to the average recommended date led to risk reduction while wheat yield was more risky when planting date was delayed by 30 days. In Khorasan Razavi province the recommended planting date resulted in lower risk but yield risk was increased by earlier planting. In Southern Khorasan province wheat yield was subjected to minimum risk and higher stability when the recommended planting date was delayed by 30 days. It was concluded that the low potential wheat yield particularly in Southern Khorasan could be due to management practices and higher yield with low risk could be achieved with improvement of the current management operations.\ud \ud Key words: Risk analysis, Monte Carlo simulation, Wheat, Yield stability, Agroecological zonatio

Radiation Absorption and Use Efficiency in Relay Intercropping and Double Cropping of Winter Wheat and Maize

Abstract\ud In many parts of the country farmers are faced with the problem of synchrony between sowing date of spring crops and the grain filling period of winter cereals. Competition for limited resources, mainly water results in delayed sowing in spring. In this research relay intercropping of winter/spring species was studied as an alternative practice for conventional double cropping system. Four intercrop treatments with ratios of 3:1, 3:2, 4:2 and 6:2 (wheat:corn) together with sole crop of each species was evaluated in a randomized complete block experiment with 3 replications. Corn seeds were sown in pre-established rows within wheat strips 32 days before harvesting wheat. During the growth period leaf area index, fraction of transmitted radiation and dry matter production was measured in two-weekly intervals and grain yield of species at harvest. Absorbed radiation during the season, radiation use efficiency of species, harvest index and land equivalent ratio were calculated based on the collected data. The results indicated that in all sowing ratios absorbed radiation by the intercrop canopy was significantly higher than sole crops. However, radiation use efficiency of species was not differed between treatments. As indicated by land equivalent ratio, relay intercropping treatments had yield advantage of 27 to 31% over sole crops which was mainly due to increased light absorption by the intercrop canopies. While the number of wheat rows had no drastic effects on the yield, the best results was obtained from 3:2 (wheat:corn) intercrop. It was concluded that relay intercropping of winter cereals with spring crops results in better utilization of resources and increased yield compared to double crop of the same species.\ud \ud Keywords: Relay intercropping, Radiation absorption, Radiation use efficiency, Competition, Land equivalent ratio, Yiel

The Effect of Split Nitrogen Application on Patterns of Dry Matter partitioning in Sugar beet

Abstract\ud The effect of split application of nitrogen fertilizer on dry matter (DM) partitioning patterns, yield and quality of sugar beet was studied in a field experiment at Brat Abad, Fariman during 2001 growing season. Three levels of nitrogen fertilizer (N ,70 ; N2 ,140 ; N3 ,210 kg N/ha) were split as S1, %100 at sowing ; S2, %75 at sowing and %25 at thinning; S3, %50 at sowing and %50 at thinning ;S4, %25 at sowing and %75 at thinning. Factorial experiment based on a randomized complete block design with 4 replications was used. Dry matter partitioning towards storage roots in N1 and in N2 treatments switched at 66 and 76 day after emergence, respectively. In S1 spliting pattern more DM was allocated to root in all growth stages. So that in 1400 GDD (5 Aug) amount of dry matter partitioning to storage roots and tops was equal to %50 while at this stage, partitioning of dry matters to storage roots in S2, S3 and S4 were % 47, % 44 and % 38 , respectively. Nitrogen levels had significant effect on polarity, Na, K, recoverable sugar yield, white sugar content and molass sugar. However, these effects on root and sugar yield and N-amino was not significant. Higher rates of nitrogen fertilizer, led to decrease in polarity, white sugar content and recoverable sugar yield. However, root yield, Na, K, N-amino and molas sugar increased in response to N levels. Maximum net sugar yield (4.4 ton/ha) was obtained in the lowest N application. In this study, effect of different patterns of nitrogen spliting and interaction between spliting patterns and nitrogen rates on quality and quantity of sugar beet was not significant. However, maximum net sugar yield (4.8 ton/ha) was obtained in N1S1 where the lowest level of N fertilizer was applied at sowing. \ud \ud Keywords: Sugar beet, Dry matters partitioning, Root yield, Sugar yield, Nitroge

Assessment of Sesame and Chickpea Yield and Yield Components in the Replacement Series Intercropping

Abstract\ud This experiment was carried out for assessment of sesame and chickpea intercropping under climatic condition of Mashhad. The Experiment included main factor A (planting methods) whit two levels a1(row planting) and a2(mixed planting) and factor B (replacement planting pattern) consisting of five levels b1 (chickpea monoculture), b2 (75% chickpea+25% sesame), b3 (50% chickpea+50% sesame), b4 (25% chickpea+75% sesame) and b5 (sesame monoculture) and was carried out in context of split plot based on randomized complete block design with three replications. results indicated that was significantly affected land equivalent ratio, that 50% chickpea+50% sesame and 75% chickpea+25% sesame row ratios with 1.46 and 1.34 respectively had the most and treatment 25% chickpea+75% sesame mixed with 0.94 had the least land equivalent ratio. So, according to these results, intercropping of sesame and chickpea with ratio of 50% optimum density of chickpea + 50% optimum density of sesame and 75% optimum density of chickpea + 25% optimum density of sesame under climatic condition of Mashhad is considerable.\ud \ud Keywords: Yield components, Harvest index, Land equivalent ratio, Row intercroppin

The Effects of Time of Manure Application and Different Biological Fertilizers on Quantitative and Qualitative Characteristics of Cucurbita pepo L.

Abstract\ud To study the response of summer squash as a medicinal plant, two manure application time and utilization of different biofertilizers, split plot arrangement of factors based on randomized complete block design with three replications was used in 2008-09 growing season. Two manure application time (autumn and spring) were allocated to main plots and four biofertilizers including 1- Nitragin (containing Azotobacter sp., Azospirillum sp. and Pseudomonas sp.), 2- phosphate solubilizing bacteria PSB (containing Pseudomonas sp. and Bacillus sp.), 3- Nitragin+PSB, 4-control, were assigned to sub plots. The results showed the significant effect of spring manure application on fruit and seed yield. Nitragin increased fruit and seed yield, significantly. The superiority of spring manure application was revealed on seed and fruit number. A positive correlation (R2 = 0.92) was found between fruit and seed yield with a linear trend in the range of 10 to 20 t ha-1 and leveling off at the above 20 t ha-1 fruit yields. The seed oil and protein content were not affected by treatments, however, the biofertilizers increased oil and protein yield compared to control. At a glance, the biofertilizers could be an appropriate alternative for chemical fertilizers to achieve ecological production of summer squash. \ud \ud Keywords: Schneider Squash, Biofertilizers, Seed yield, Seed oi