Phosphorus (P) deficiency is invariably a common crop growth and yield-limiting factor in unfertilized soils, especially soils high in calcium carbonate, which reduces P solubility. Even when such soils are fertilized, adsorption and desorption lead towards a reversion to stable and less soluble P forms, thus reducing fertilizer use efficiency. Field trials that examine the implications of such P reactions and residual fertilizer P responses in the field are relatively rare in Mediterranean environments. A 5-year field experiment in southern Turkey examined the residual effects of repeated P fertilizer applications for corn production in a calcareous soil Typic Xerofluvent. Following the initial year's fertilization (0, 33, 66 and 99 kg P ha À1 ) to establish a range of soil P levels in subsequent years, the main plots received 0, 9, 18, 27 and 36 kg P ha À1 annually. Grain P uptake was calculated for each year and used in the prediction of P recovery. All plots were sampled and analyzed for available P prior to planting with a local corn hybrid. Soil P values increased with the initial P levels (8-24 mg kg À1 ) but declined after 3 years (6-10 mg kg À1 ). Only the lowest annual P application rate (9 kg P ha À1 ) produced an available P level that was not in the sufficiency range. Grain yields across the main and subplots and years ranged from 6.6 to 13.2 t ha À1 . Overall corn yield averaged over the years increased by 8-33% compared to the control as the rates of applied P increased. However, P application had no effect in a year when below-average rainfall restricted crop growth. A residual P effect on grain yield occurred with higher P application levels in the last year. Leaf and grain P concentrations were in the sufficiency range in general. Grain P uptake was calculated for each year and used in the prediction of P recovery. Actual recovery was higher with low P application rates and ranged between 10.8 and 46.4%. The study indicated that under irrigated conditions, corn is likely to respond to P fertilization, but that buildup of available P can occur within a few years and adequate plant available P levels can be maintained by modest P fertilizer application rates.

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In the Mediterranean region, much emphasis is placed on the role of fertilizers in enhancing crop production to achieve food security. Given the complex nature of phosphorus (P) reactions in soils, considerable research has dealt with fertilizer aspects related to efficient P use, but comparatively less emphasis has been given to plant variation with respect to P efficiency. In this study, selection and adaptation of P-efficient corn genotypes was seen as one possible approach to enhancing P efficiency. Thus, a greenhouse experiment with 10 corn genotypes (traditional to modern), five P application rates (0-200 mg kg 21 ), and four field trials with three genotypes for 2 years were carried out on various calcareous soils (Vertic Torrifluvent, Vertic Calciorthid, Entic Chromoxerert, and Typic Xerofluvent). Measurements were made of root characteristics. Treatments in the field trials were five P application rates as main plots (0-68 P ha 21 ) and three corn genotypes as subplots. Genotypes were selected for the field trials from the greenhouse experiment as ''efficientresponsive,'' ''efficient-nonresponsive,'' and ''inefficient-responsive.'' Dry-matter (DM) yield and plant P uptake by plants increased with P application rates in the greenhouse experiment. Root length and mass were considerably increased by increasing P levels. Genotypes were classified for P efficiency. The studies indicated that because corn genotypes respond to P-fertilizer application differently, this trait could be utilized to exploit native and applied P more efficiently, especially at low levels of available P and when P-fertilizer use is limited. This differential response derives from morphological, physiological, and genetic variability among the genotypes. Although genotypic efficiency is important for fertilizer management, the contribution of the efficiency is not a substitute for fertilizers, especially if high yields are required. Nevertheless, breeding for P-use efficiency should be a component of any program to improve crop yield potential.

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ÖzBu çalışma melez mısır ıslahında in-vivo katlanmış haploid hatların elde edilmesi çalışmasında kullanılan farklı induzer genotiplerin haploid indirgeme oranlarının tespit edilmesi amacıyla 2014 yılında Doğu Akdeniz Tarımsal Araştırma Enstitüsü'nde yürütülmüştür. Çalışmada induzer olarak (haploid indirgeyici ve toz verici) RWS, RWK-76 hatları ile bu hatların melezi olan RWS X RWK-76 melezi ve Stock-6 hattı kullanılmıştır. Haploid tohum elde etmek amacıyla ana (toz alıcı) olarak, toplamda 75 farklı genotip kullanılmıştır. Bunlardan 66'sını Doğu Akdeniz Tarımsal Araştırma Enstitüsü mısır ıslah çalışmaları kapsamında elde edilen F 2 kademesindeki materyal, 9'unu ise ticari hibrit çeşitlerin açıkta tozlanması ile elde edilen populasyonlardan seçilen 9 farklı genotip oluşturmuştur. Induzer olarak kullanılan genotiplerin haploid indirgeme oranları çalışmada ana (toz alıcı) olarak kullanılan genotiplere göre değişiklik göstermiştir. Ana olarak kullanılan 75 genotipten 69'undan toplam 1463 adet haploid tohum alınmıştır. Haploid tohumların seleksiyonu renk markörüne göre yapılmıştır. En yüksek haploid tohum oranı %7.80 ile induzer olarak kullanılan RWK-76 hattından elde edilmiştir. En düşük haploid tohum oranı ise %1.28 ile induzer Stock-6 hattından alınmıştır. Yapılan çalışmada ortalama haploid tohum elde etme oranı %4.79 olarak saptanmıştır. Determination of Haploid Induction Rates of Different Inducer Lines Used for In-Vivo Double Haploid Technique in Hybrid Maize Breeding AbstractThis research was conducted to determine haploid induction rate (HIR) of different inducer lines used for in-vivo double haploid technique in hybrid maize breeding at the East Mediterranean Agricultural Research Institute. In the study RWS, RWK-76 inducer lines, their cross RWS X RWK-76 and Stock-6 were used as male parent for haploid induction. In the study 75 different F 2 genotypes as female parent were used for haploid seed production. The 66 of F 2 genotypes were selected from the corn breeding material of East Mediterranean Agricultural Research Institute, and 9 genotypes were selected from open pollinated populations of the commercial hybrid cultivars. Results of the study showed that haploid induction rate of different inducer genotypes changed depending on the female parent. It was obtained 1463 haploid seeds from 69 F 2 genotypes of total 75 F 2 genotypes. The highest haploid induction rate (7.8%) was obtained from the inducer RWK-76 line, while the lowest haploid induction rate (1.28%) was obtained from the stock-6, and average haploid induction rate (HIR) was 4.79%.