THE INFLUENCE OF N AND P FERTILIZATION ON WINTER WHEAT YIELD

: Wheat is an essential crop for global food security, and for good development and to achieve satisfactory yields wheat needs favorable climatic conditions and adequate nutritional support. Was executed a bifactorial experience, of the AxB model A - phosphorus doses: P 0 ; P 40 ; P 80 ; P 120 ; P 160 and B - nitrogen doses: N 0 ; N 30 ; N 60 ; N 90 ; N 120 . The research carried out during the period 2020-2022 aimed to determine the optimal doses of the two nutrients for the autumn wheat crop in achieving the most efficient yields. Nitrogen is the factor with the greatest contribution to the formation of yield, an amount of 30 kg/ha s.a. can bring an increase in yield of 22%, growth that decreases with the additional application of others 30 kg/ha s.a. N. Phosphorus has a lower contribution to yield, as a unilateral factor, but it is important in plant nutrition, especially as a support for nitrogen.


INTRODUCTION
The main current challenges of humanity are aimed at reducing the causes of global warming, adapting to climate change and providing enough food for the world's population.
Wheat (Triticum sp.) it is an essential crop for global food security, the main and the secondary yield having numerous uses in human and animal nutrition but also as a raw material for industry.
The yield potential of wheat has increased in recent years also due to the improvement of new varieties and technological and soil management practices.
For good development and to achieve satisfactory yield, a crop needs favorable climate conditions and an adequate nutritional support, especially rich in macro elements. Soil organic matter is the main source of nitrogen for plants, and to avoid exhausting the natural state of the soil, mineral or organic fertilizers are applied to be available to the plants throughout the growing season.
The use of fertilizers as a source of nutrients is essential for the yield of agricultural crops. In phosphorusdeficient soils, application of P fertilizers can help increase yields, however, the response of the wheat crop to phosphorus fertilization may not be significant when the amount of phosphorus in the soil is greater than the plant's requirements.
The formation of wheat yield starts from the first phases of vegetation, and proper fertilization and a sufficient amount of water in the soil can lead to an important increase in yield. To ensure a high yield, wheat needs available nitrogen in different amounts depending on the potential of the variety, soil moisture, soil texture and crop development stage.
Nitrogen is the most important nutrient element involved in plant development (Agapie et al, 2021), significantly influencing their yield. Plants take up nitrogen when their roots begin to develop until maturity, when the absorption process stops. Nitrogen is often the most deficient of all nutrients required by a crop in the process of yield and quality formation.
The amount of phosphorus in the soil can be influenced by microbial activity (Waldrip et al, 2011) and may become available to plants in varying amounts depending on soil type and environmental conditions (Guo et al, 2000). Compared to chemical fertilizers, organic fertilizers can provide more phosphorus (Xavier et al, 2009) available to plants.
The N/P interaction is consecrated and much promoted because, through the balance of the roles of these elements, by the specificity of the effects, it can be appreciated as a determinant in large and quality agricultural yields. The increases in yields obtained with NP applications exceed those of individual applications and the basis of this observation there is the quality of reciprocity of the two elements to contribute to their better exploitation (Rusu, 2021) Fertilization in a rational way by using large amounts of fertilizers leads to soil acidification (Barak et al, 1997, Darusman et al, 1991, environmental pollution and soil degradation (Ahmed et al, 2017), and their longterm application has a negative impact on physical and nutritional properties (Das et al, 2017).

MATERIAL AND METHOD
The experience was located at Agricultural Development Research Station Turda (ARDS Turda) on the cambic para-rendzina epi-calcaric chernozem clay type (after SRTS 2012+). The soil profile has the following physical characteristics: clay-clay texture, the clay between 33,45 and 52,21 mm, fine pores, moderately compact, clear transition from one horizon to the other. As a chemical description, the soil has a slightly alkaline neutral pH, neutral to high humus content, well-supplied in nitrogen and potassium, moderate in phosphorus.
The experiment is bifactorial, of the AxB model, with the factors: A -Phosphorus doses (P0; P40; P80; P120; P160) and factor B -Nitrogen doses with five graduations (N0; N30; N60; N90; N120). Phosphorus was applied in the fall before plowing to be incorporated into the soil, and nitrogen was applied fractionally, 50% of the quantity was administered at sowing and 50% in the spring, when vegetation resumed.
Research executed during 2020-2022 aimed to determine the optimal doses of the two nutrients for the winter wheat crop in achieving the most efficient yields.
The biological material was represented by the Codru winter wheat variety created at ARDS Turda, sown at the density of 550 germinative grains/m 2 , with soybean as a preceding crop.
During the growing season, two treatments were executed out to maintain the phytosanitary status of the crop. The first treatment involved the use of a herbicide based on amidosulfuron and one based on 2.4D for the control of dicotyledonous and monocotyledonous weeds, a fungicide based on tebuconazol for foliar diseases and an insecticide based on acetamiprid for pest control.
The second treatment was executed with the aim of protecting the wheat crop from pests that can cause problems for the crop in the ear emergence phase, being used an insecticide based on tau-fluvanilat and a fungicide based on protioconazol.
The obtained results were statistically processed by the variance analysis method and the lowest significant difference was determined -DL -(5%, 1% and 0.1%) (ANOVA, 2015).
The analysis of the evolution of precipitation in the Turda area during the reference period shows that the summer season is becoming increasingly hot and drier, winters are getting warmer and drier, meteorological extremes can cause very large losses in agriculture.
From the analysis of the average monthly temperature, there is an increasing trend compared to the multiyear average throughout the year, with the deviations recorded in the three years reaching values of 4.9ºC (table  1).
Periods with temperatures above normal favored a higher water consumption than in conditions of normal temperatures, consumption which, correlated with the rainfall deficit, made its presence felt especially in the experimental year 2020. The lack of rainfall in the months of April and May led to the drying almost entirely of the tillers, the yield being made only of the main spike.
In the second experimental year, rainfall recorded monthly variations, but with fairly small deviations from the average, which makes the agricultural year 2020-2021 to be favorable for wheat cultivation.
The year 2022 was a predominantly dry year, but the fact that during the formation of the yield, the climatic conditions did not register significant deviations from the average, the wheat crop developed normally, except at the end of the growing season when there has been a rush of vegetation phases, the wheat reaching maturity before the onset of the severe drought in June and July (table 2).

RESULTS AND DISCUSSIONS
Climatic conditions during the growing season are the main factor that determines the crop yield, especially in areas where the only source of water is from rainfall and groundwater. Monitoring of climatic conditions provides certain answers for yield results, as he also states de Avila et al (2013) water stress, excessive rainfall and extreme temperatures can significantly reduce crop yield.
The increase in temperatures associated with the lack of precipitation can speed up or slow down growth processes and implicitly reducing the accumulation of reserve substances in the grain, having the effect of reducing yield. In the accumulation and preservation of water in the soil, an important role is also played by the preceding plant, because where a plant releases the land early the water reserve will be restored faster than where the plant will be harvested later, and a large water-consuming plant will leave a very low water reserve in the soil. Because of soil fluxes it is difficult to say exactly what the true value of available soil water is and how much is actually used by plants, but as long as there is a high-water reserve in the soil, even if the processes of evaporation of water from the soil and evapotranspiration from plants are high, the plant will properly use the water in order to carry out the processes.
Compared to the average of the three years studied, the yields of the years 2021 and 2022 they were superior, the differences recorded in the two years being statistically very significant. Opposite the year 2020, year in which the lack of precipitation from April to May left its mark on plant development, effect observed by the very significant decrease in the yield of -1243 kg/ha compared to the average of the three years studied.
Although in the year 2022 there was a significant pluviometry deficit, the wheat variety used in the experiment was able to utilize the soil water reserve very well and achieve an average yield of 6274 kg/ha (table  3).
A properly fertilized wheat crop has more vigorous growth and better development of root biomass which will extract water and nutrients from the soil, by comparison with a crop that is less fertilized and which is obviously lower in vegetable mass. The influence of the preceding plant and the type of soil on yield is eloquent, so in the unfertilized version a yield of 4097 kg/ha was recorded. In a rational rotation and on soils with high fertility even without the support of fertilization, acceptable yields can be obtained.
Following the application of different doses of N, an increase in yield of up to 53%, compared to the unfertilized version, percentage difference achieved by applying a 120 kg/ha s.a. N, the constant increase in the nitrogen dose being reflected in the increase in wheat yield, the results obtained being similar to those obtained by Haile et al (2012), who reported that yield increase increased with nitrogen dose. Westfall et al (1996) they also noted that the nitrogen dose is the dominant factor in obtaining yields in optimal pluviometry conditions.
The increase in wheat yield is closely related to the increase in nitrogen dose, but the biggest difference (895 kg/ha) is observed between the control dose and the dose of 30 kg/ha s.a. N, the other doses registering slightly smaller differences compared to the previous dose, comprised between 703 and 272 kg/ha, continuously decreasing with the additional application of 30 kg/ha s. a. N (table 4).
The yield results obtained in the three years confirm that nitrogen is an essential nutritional element in obtaining satisfactory yields, the yield differences recorded since the application of the first dose having statistical significance, similar results obtained by Maadi et al (2012) which showed from the studies they realized that the application of nitrogen significantly increases the yield of cereals. The greatest difference in yield between doses of P was observed when applying the first dose compared to the unfertilized control, the increase in yield achieved when a dose is applied of 40 kg/ha s.a. P of 726 kg/ha, difference that is no longer found when applying the other doses.
Supplementation with 40 kg/ha s.a. P contributes to increased yield but the differences from one experimental variant to another are contained between 144 and 208 kg/ha, phosphorus being more of a support for nitrogen and less of a primary element in achieving wheat yield (table 5).
Even though P supplementation of the crop brings significant increases in yield, the difference between the control dose and the highest dose is only 27%, much lower than in the case of nitrogen, nitrogen showing its superiority over P in the case of the influence of nutrients in achieving of wheat yield. Lu et al (2020) states that in phosphorus deficient soils, application of P fertilizers can help increase the yield of agricultural crops. The response curves to the different doses of phosphorus, shown in figure 1, are not very pronounced, in agricultural holdings larger than P, yields show a range which suggests that wheat does not require high phosphorus fertilization to achieve considerable growth. High doses of phosphorus exceeding the dose of 120 kg/ha s.a. they are not economically justified by the yield achieved.
The yields obtained as a result of the interaction of nitrogen and phosphorus doses are increasing simultaneously with the increase of N and P doses from 3707 kg/ha, yield registered in the unfertilized version and up to 6885 kg/ha yield recorded when applying the highest doses of N and P, as is N120P160 (figure 2).
Phosphorus intake in achieving wheat yield emerges from the results obtained following the application of nitrogen in the variants without phosphorus fertilization, by the fact that no significant increases in pyield are recorded at high doses of nitrogen, only when applying average doses of 30-60 kg/ha s.a. N. With the application of phosphorus, differences in yield are also recorded between the doses of nitrogen, the importance of phosphorus as a support for nitrogen being very obvious.

CONCLUSIONS
The behavior of the biological material when applying mineral fertilizers was good, the wheat crop reacting positively to the application of both N and P doses.