International Journal of Plant Production
Volume:6 Issue: 1, Jan 2012

A study was carried out over 2 years (2008/2009 and 2009/2010) in Greece, in order to evaluate the weed control using reduced rates of the herbicide mesosulfuron-methyl+iodosulfuron-methyl-sodium of four major weeds (Avena sterilis, Phalaris minor, Papaver rhoeas and Sinapis arvensis), grain yield and yield components of five wheat cultivars (Bob, Cosmodur, Meridiano, Quadrato and Simeto). The results indicated a significant differentiation between the several wheat cultivars regarding their weed competitive ability, in terms of dry biomass and seed production. In the case of cultivars such as Simeto the efficacy of 50% reduction of the herbicide recommended rate on wild oat remained high, since it resulted to a reduction of biomass and seed production up to 81 and 98% compared with the untreated plots. In most cultivars studied, the reduction of the herbicide rates by 25 to 50% resulted to a no significant reduction of grain yield compared to the recommended rate. The study revealed that some wheat cultivars with enhancing weed competitiveness can improve the efficacy of reduced herbicide rates. Consequently, sustainable cropping systems could be further developed through the integration of such agronomic practices, while in parallel, care on the threat of herbicide resistance development should be also taken

The aim of this study was to identify leaf physiological traits, which could be used in selecting high yielding genotypes among 12 sugar beet cultivars grown in two contrasting pedo-climatic environments. In the stressful Site 1 (high temperatures, low rainfall, heavy-textured soil), high yielders had cooler leaves (lower ΔT) and thus, transpired (E) and photosynthesized (A) more. Also, these cultivars had higher chlorophyll content, as assessed by SPAD readings, supporting that staying green under stress conditions contributes to final yield. On the contrary, in the favorable Site 2 (mild temperatures, high rainfall, light-textured soil), high yielding cultivars had higher leaf area index (LAI> 3.5-4.0). In Site 2, a negative correlation between SPAD and yields (fresh root weight-FRW and sugar yield-SY) indicated that the investment in high leaf greenness under favorable conditions is a disadvantage for sugar beet productivity. Combining data of both sites, the optimum values of physiological traits related to yields (FRW and SY) were estimated, respectively, at -0.59 to -053 ºC for ΔT, 20.37 to 19.26 μmol m-2 s-1 for A and 8.97 to 8.86 mmol m-2s-1 for E. It is proposed the use of SPAD as an easy, rapid and non-destructive screening for sugar beet high yielders under both stressful and favorable growing conditions.

In Cambodia, cassava is mostly grown with little or no fertilizer inputs, but the magnitudes of nutrient balances are not known. This study was conducted to assess nutrient balances for cassava cultivation in Kampong Cham province in Northeast Cambodia. Forty five households in four cassava production zones were interviewed in relation to their cultural practices and crop residue management, upon which sources of nutrient inputs and outputs were based. Chemical fertilizer, manure, planting materials and rainfall were the defined inputs, while cassava roots and stumps were the outputs. Crop cutting was undertaken in the cassava fields of the 45 households to obtain weights of roots and other plant parts. Nutrient balances were calculated for the individual fields based on nutrient contents of the component sources obtained from the literatures. The results showed negative balances for all the nutrients evaluated. The imbalances were most serious for N, K and Ca with the averages of -64.45 kg N, -52.83 kg K and -10.83 kg Ca ha-1, but were less serious for P and Mg with the averages of -2.85 kg P and -7.20 kg Mg ha-1. These negative balances were the consequence of low nutrient inputs in current practices where only a few farmers applied low rates of chemical fertilizer or manure. Continued use of current practices will threaten the sustainability of cassava production in Cambodia. For long term productivity of the crop, the application of organic manures together with lime and chemical fertilizers high in N and K is recommended. Keywords: Soil nutrients; Agricultural sustainability; Soil fertility management

In Greece and Turkey, okra (Hibiscus esculentus L.) is cultivated for small pods (≤4-5 cm), which are highly perishable after harvest. In this experiment, okra was cultivated at 4 levels of N (30, 150, 300 and 450 mg l-1) within the irrigation water. Pod yield was highest at 300 mg l-1 N. High N increased the nitrate content and decreased dry matter without affecting pod colour (P<0.05). When pods were enclosed in polyethylene and stored for up to 10 days at 7 or 10 oC fresh weight decreased by 7% and 11-12% respectively, and by 20% and 28% respectively during 3 days subsequent shelf-life at 22 oC. Weight loss after 10 days at 7 oC and during shelf-life was higher in pods from 300-450 mg l-1 N and was accompanied by a corresponding decrease in % dry matter. The loss of chlorophyll during storage (i.e. increase in a*) rose with storage time and N application level, accompanied by a decrease in b*. The nitrate concentration within the pods decreased with storage irrespective of N level. It is concluded that the rate of N application affects not only the production but also the quality of okra during storage. For the production of small-sized pods N application should not exceed 300 mg l-1. Although pods from high N levels (300-450 mg l-1 N) lose more weight, dry matter and chlorophyll than those from the lowest N level (30 mg l-1 N), they may nevertheless be stored satisfactorily for up to 10 days at 7 oC, which permits a 3 day ambient shelf-life.

Long-term yield performance and yield stability of common cropping systems needs to be simultaneously assessed at various fertility regimes. Based on a consecutive 19-year field trial, including eight fertilization treatments with different combinations of nitrogen (N), phosphorus (P), potassium (K) and recycled manure (RM), the effects of fertilization and crop rotation on corn (Zea mays L.) yield performance and stability were evaluated. The results showed that although the fertility regimes had greater influence on yield increase (average 2.94 Mg ha-1) than crop rotation (averge 0.42 Mg ha-1) [corn-corn-soybean (Glycine max)], the rotation effect on yield increase was almost 51% of that of fertilizer N under low nutrient availability conditions. A synergistic effect between RM and crop rotation was observed in the present study, in detail, yield-increasing effect of RM, on average, were 0.98 and 1.04 Mg ha-1 in continuous and rotation cropping systems, respectively. Stability analysis revealed that RM improved yield stability under nutrient absence conditions rather than under balanced fertilization conditions. Moreover, crop rotation substantially improved yield stability. High and stable yields were obtained in test years with arid index ranged from 1.08 to 1.16, which can be regarded as proper environment in this region. Ranking the statistical parameters indicated that they are similar in general, and considering the amount of RM resource, NPM which achieved high and stable yield was the most recommendable fertility regime in this region.

Irrigation water is limiting for crop production in arid and semi-arid areas. Furthermore, excess nitrogen (N) application is a source of groundwater contamination. Partial root drying irrigation (PRD) can be used as water saving technique and a controlling measure of groundwater N contamination. The objectives of this investigation were to evaluate the effect of ordinary furrow irrigation (OFI), variable alternate furrow irrigation (VAFI) and fixed alternate furrow irrigation (FAFI) and different N application rates (0, 100, 200, and 300 kg ha-1) on maize yield and yield quality, drainage water, N leaching, uptake and N use efficiency (NUE). Results indicated that the interaction between irrigation treatments and N application rates was statistically significant for all treatments applied in this investigation. Maize grain yield was reduced by alternate furrow irrigation due to high sensitivity of maize to water stress, however, in case of water shortage, VAFI is superior to FAFI. In the study region, N application of 200 kg ha-1 is optimum for maize grain yield to obtain optimum grain yield, NUE and N-yield efficiency. Drainage water and total leached nitrate decreased for VAFI and FAFI as compared to OFI and their amount were lowest for FAFI (drainage water) and in VAFI (total leached nitrate), respectively. Total leached nitrate bellow the root zone increased in response to the increase in total available nitrogen for water applications higher than crop ET. N loss was reduced for FAFI and VAFI for N application rates of 200 and 300 kg ha-1. Only for FAFI and VAFI, the N uptake decreased and the soil residual N increased as compared with OFI. Thus, in order to avoid N loss, the amount of N fertilizer should be reduced in proportion to the amount of soil water available for plant uptake under deficit irrigation. Furthermore, it was indicated that leaf level stress sensitivity index (LLSSI) was higher for VAFI and it was about 2.5 times of OFI.

Restricted water resources are a limiting factor for irrigation applications throughout the world. The effects of irrigation regimes (amount) on cotton lint yield are known, but there is little information on the effect of irrigation regimes on seed quality of cotton. In this study, the effects of deficit irrigation after the onset of flowering on lint yield and seed quality of cotton (Gossypium hirsutum L.) with a drip irrigation system were evaluated during 2006 and 2007 in the northern Iran. After the onset of flowering, four irrigation regimes (0, 40, 70 and 100% of Class A pan evaporation (%PE)) were applied when the cumulative evaporation amount from class A pan reached approximately 40-50 mm. Lint yield showed a quadratic response to %PE and maximum lint yields were achieved with 82 and 91% PE irrigation regimes in 2006 and 2007, respectively and seed quality (based on standard germination and seed vigor tests) increased with a decrease in deficit irrigation. Thus when the amount of applied water was reduced by 30 (70% PE) and 60% (40% PE), decrease in lint yield was about 4 and 14%, respectively. The results of this study showed that irrigation treatments of 40-70% PE would be optimum for lint yield and seed quality production under drip irrigation.

The effect of row spacings and irrigation levels on the earliness of seed production of cotton was investigated under the Mediterranean environment of central Greece. This particular cotton growing area is exposed to risk of autumn rainfall that might cause low seed quality in fields allocated primarily for seed production. Two varieties of cotton, Celia and Hersi, were planted in two row spacings (93 and 75 cm) and two irrigation levels (normal and low levels 6160 and 3080 mm ha-1). No significant difference in the yield was found among the two varieties, nor between the two row spacings. The low irrigation level had significantly negative effects on the number of squares, bolls, total dry weight and seed cotton production when compared with irrigation level. However, the low irrigation level resulted in a harvest earlier by ten days, which contributed to avoiding autumn rainfall. Seed quality (measured by germination and Warm-Cold Vigour Index Test) was better in seeds from the low irrigation level than in those from the normal irrigation level. Although yield of both varieties was higher under normal irrigation, seed quality was lower compared to low irrigation level. This was evidenced by the higher Free Fatty Acid (FFA) in “normally” irrigated plants. The results of this study showed that low irrigation level offers substantial benefits for early harvesting and production of high seed quality. Moreover, the FFA could be successfully employed as a quick criterion for seed quality ranking.

The snow-cover on soil, the factor that protects wheat from the biting cold, has generally declined; on the other hand, the surface air temperature has warmed. It is not clear whether these changes decrease winter-killing of wheat or favor it in Iran. Therefore, this study was mainly aimed to determine the past trend in frequency of winter-kill events (Y) for wheat with -4 oC frost tolerance, using the framework of acclimation/de-acclimation of wheat to temperature. The rate of change in Y was estimated over phases I (frost tolerance increases with decreasing temperature; hardening), II (it shows plateau state for a period with coldest temperature), and III (it decreases with warming; de-hardening) of wheat response to temperature. The input data for model was 39 to 44 years daily weather data for five locations as representative of major agricultural zones in Iran. The results indicated that the surface air temperature has warmed; consequently, the value of snow-falling has been decreasing and changes in acclimation/de-acclimation of wheat over the phases found to be happened in slowed manner. Over phase I, the frequency of winter-killing has remained constant just for Shiraz; for other four locations, the value of frequency has decreased (0.9 to 3.8 times decade-1). Over phase II, the decline varied between 0.8 to 4.7 times decade-1 across all five locations. Over other phase, the frequency has shown downwardly trend (1.3 to 3.7 times decade-1) just for three locations. Generally, it can be said that the over-wintering survival has been improving during past decades.