اثرات خاك‌ورزي و مديريت فسفر بر لايه‌بندي فسفر در سيستم توليد ذرت دانه‌اي

Tillage and Phosphorus Management Effects on Stratification of Phosphorus in a Grain Corn Production System

فسفر از عناصر ضروری در تغذیه گیاهان زراعی است كه در صورت عرضه بیش از حد می‌تواند محدود‌كننده رشد یا آلوده‌كننده محیط زیست باشد. از طرف دیگر عملیات خاك‌ورزی تأثیر مستقیمی بر رفتار و قابلیت جذب فسفر خاك دارد. بر این اساس طی آزمایشی تأثیر مدیریت خاك‌ورزی و كود فسفره بر غلظت فسفر قابل‌استفاده در اعماق مختلف خاك و عملكرد ذرت دانه‌ای مورد‌بررسی قرار گرفت. آزمایش به‌صورت اسپلیت‌فاكتوریل در قالب طرح بلوك‌های كامل تصادفی در سه تكرار انجام شد. روش‌های خاك‌ورزی به‌عنوان كرت اصلی در دو سطح مرسوم و كم‌خاك‌ورزی و مدیریت كود فسفره به‌عنوان كرت‌های فرعی شامل دو عامل مقادیر مختلف كود فسفره در سه سطح: 75، 100 و 125‌درصد توصیه كودی و روش‌های كوددهی در سه سطح: پخش سطحی، جای‌گذاری عمقی و نواری به‌صورت فاكتوریل بود. نتایج آزمایش نشان‌داد، تهیه بستر با روش كم‌خاك‌ورزی موجب بیش‌ترین مقدار غلظت فسفر در عمق (صفر-15) خاك گردید و عملیات خاك‌ورزی به روش مرسوم با استفاده از گاوآهن‌برگردان‌دار, از نظر مقدار غلظت فسفر با 2/7‌درصد كاهش در رتبه دوم قرار گرفت. كمترین مقدار غلظت فسفر در عمق (صفر-15) سانتی‌متری خاك، مربوط به كاربرد كود فسفره براساس 75‌درصد توصیه كودی و بیش‌ترین میزان غلظت فسفر در شرایطی حاصل شد كه مقدار كود فسفره مورد‌نیاز براساس 125‌درصد توصیه كودی مصرف گردید. تأثیر روش‌های مختلف خاك‌ورزی بر عملكرد ذرت دانه‌ای غیر‌معنی‌دار بود. بیش‌ترین عملكرد از روش كم‌خاك‌ورزی به‌دست آمد و تیمار خاك‌ورزی مرسوم بدون داشتن اختلاف معنی‌داری در رتبه دوم قرار گرفت. میزان عملكرد ذرت دانه‌ای در واكنش به روش‌های مدیریت كود فسفر اختلاف معنی‌داری را نشان‌داد. كمترین مقدار عملكرد مربوط به كاربرد كود فسفره براساس 125‌درصد توصیه كودی به‌دست آمد. استفاده از دستگاه كودكار‌ بذركار (روش نواری) موجب تولید بیش‌ترین مقدار عملكرد گردید و كاربرد كود به روش عمقی در رتبه دوم قرار گرفت.

</strong >Introduction </strong > Phosphorus (P) is an essential element in crop nutrition, which can be growth limiting or an environmental contaminant, if present in excess. On the other hand, tillage practices have a direct effect on behavior and availability of soil P. Since, application of different tillage methods lead to different patterns of soil phosphorus distribution, hence P fertilizer needs and P availability may be different in tillage systems. Researchers have found that the effects of tillage on P stratification depends on soil texture. Kimmel et al. (2000) reported that total P losses were significantly lower for NT than chisel-disk-field cultivator and ridge-till. Bahgar et al. (1998) showed that higher levels of P fertilizer improved shoot, root growth and the uptake of all nutrient elements in No till system. High levels of P also significantly enhanced the uptake of all nutrient elements except Zn and Cu. </strong >Materials and Methods </strong > This study was conducted in Darab Agricultural Research Station in Fars Province, located in the south-western region of Iran (28° 47’N , 57° 17 ׳ E ; 1120 m above sea level). The soil texture was loam. The experimental design was a randomized complete block with split factorial arranged in three replications. Tillage methods were main plots in two levels: conventional (CT) and reduce tillage (RT). Sub plots included phosphate fertilizer rates in three levels: 75%, 100% and 125% of recommended fertilizer (P1, P2 and P3, respectively) and P application methods in three levels: surface broadcast, banded starter and deep placed (M1, M2 and M3, respectively) in factorial technique. Corn hybrid 704 was planted using a four-row planter with 75 cm row spacing. Phosphorus concentration in the 0-15 and 15-30 cm soil layer and grain yield in the end of growth season were measured. </strong >Results and Discussion </strong > Different tillage systems had no significant effects on phosphorus concentration in the 0-30 cm soil layer. The results indicated that RT treatment had greater phosphorus accumulated in the surface soil (0-15 cm) and CT system reduced phosphorus concentration by 7.2%. The difference in the P concentration between the two tillage systems can be attributed over a greater depth under conventional tillage (25cm) than under reduce tillage. Different fertilizer levels had significant effects on phosphorus concentration. In P1 treatment, phosphorus concentration was significantly less than P3 treatment. The minimum and maximum accumulation of available P was observed for 75 and 125% of recommended fertilizer in the 0-15 cm soil layer, respectively. The results indicated that there was Non-significant difference between P1 and P2 treatments. Also different phosphorus application methods had significant effects on phosphorous concentration. P concentration in surface broadcast treatment increased by 11.2 and 16.5% as compared to banded and deep placed treatments. The different tillage methods× fertilizer levels× application methods interactions on phosphorus concentration were significant. The maximum phosphorus concentration were observed for RT× P3× M1 treatments in the 0-15cm soil layer and the minimum occurred for the RT× P2× M3 and CT× P2× M3, respectively. The CT× P3× M3 interaction had a greater impact in increase of phosphorus concentration. The results also revealed that different tillage systems had no significant effect on grain yield. The most of yield was observed for RT system, although there was no significant difference between CT and RT systems. Phosphorus management methods had significant effects on corn yield. The lowest yield was observed for P3 treatment. The M2 treatment led to maximum grain yield as compared with M3 treatment. </strong >Conclusions </strong > This study indicated that RT treatment had greater phosphorus accumulated in the surface soil (0-15 cm) and CT system reduced phosphorus concentration by 7.2%. It also found no difference in phosphorus concentration between tillage systems. Reduced tillage seedbed preparation method coupled with broadcast P application lead to an accumulation of available P in the surface 0-15 cm soil layer.