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» Articles | Agricultural Journals

Two 16-year-old series of experiments with winter wheat grown in rotation after winter oilseed rape were used in the study. The experiments were located in the cold temperate dry and moist climate zones on light soils. Wheat was fertilized with nitrogen in the doses of 40, 80, 120, 160, and 200 kg N·ha⁻¹ per year. Through the several years of the experiment, critical N rates for maximum yield and gross margin from the linear-plus plateau regressions were 149 ± 23.9 and 112 ± 23.6 kg N·ha⁻¹, respectively. The estimated nitrogen indicators for these doses were as follows: nitrogen use efficiency (NUE) 93 and 108%, N surplus (Ns) 6.8 and −10.1 kg·N·ha⁻¹, yield-scaled Ns, N₂O, and NH₃ 3.5 and −0.2; 0.35 and 0.30; 0.31 and 0.25 kg N·Mg⁻¹, respectively. Experiments have shown that two strategies for reducing nitrogen losses on light soils under wheat cultivation are possible: by limiting the N dose to the critical values due to the yield requirements, or due to the gross margin. The analysis of the 11-year data for 2300 farm fields with winter wheat grown on light soils showed that only 10% of them were implementing the first strategy, and as much as 90% chose the second strategy.

Mineral fertilizer production and distribution in Poland prior to 1991 were subsidized by the state. Demand for low-cost products exceeded substantially their production. During the transformation to market-oriented economy, the subsidy on fertilizers was removed and the demand from agriculture dropped dramatically. In 2008/2009 mineral fertilizer consumption reached only 122 kg nitrogen–phosphorus–potassium (N–P–K) per 1 ha and the N/P/K ratio remained 1:0.3:0.4. This tendency is disturbing because the soils in Poland are commonly acidic and poor in available K and Mg. Nitrogen fertilization and high-yielding crops compound the process of soil depletion. The objective of this article was an evaluation of soil and plant index sensitivity for soil exhaustion from P, K, and Mg. Two factorial experiments were carried on in 2003–2009 in a four-crop rotation: winter rape–winter wheat–maize–spring barley. The first factor was treatment without P, K, or Mg and a control treatment fertilized with all the macronutrients and the second one had five levels of N. For determination of plant fertilizer recommendations, official methods have been used (Egner DL, Schachtschabel). The nutrient requirements of crops were evaluated by determining the concentrations of N, P, K, and Mg in plant dry matter and N status of cereals with the nitrogen nutrition index (NNI) and Soil Plant Analysis Development (SPAD) tests. The soil was depleted for a 7-year period from analyzed macronutrients that led to a decrease of available forms of P, K, and Mg, but only a slight crop reduction. Only maize and rape crops, with high nutritional requirements, responded with a decreased yield pursuant to the lack of long-term fertilization with P, K, and Mg. There was a close correlation between K₂O exhaustion and N rates. Soil indices have been more sensitive than plant indices.

The objective of this experiment was to assess the effect of interaction between early and late nitrogen (N) fertilization on grain yield, protein content, and distribution of N between organs of winter wheat. Wheat was grown in pots in vegetation house. Experiment has been carried on in three years 2001–2003, each year in four replications. Wheat supplied with 0.9, 1.4, 1.9, 2.4, and 2.9 g N/pot was top dressed at anthesis by 0.85 g labeled nitrogen ¹⁵N/pot. Plants supplied with 0.9 g N/pot enhanced grain yield by 28% and gluten content by 62% and plant supplied with 2.9 g N/pot by 27% and 13%, respectively. The amount of ¹⁵N fertilizer stored in plant organs decreased proportionally to the amount of previously accumulated nitrogen, but the share of ¹⁵N in plant parts was almost constant. Grain accumulated about 86% of total ¹⁵N taken up by plants. Irrespective on nitrogen status prior to anthesis, about 50% of ¹⁵N has been used for gluten formation. The percentage of ¹⁵N recovery fraction ranged from 79% to 86%.

The mineral nitrogen (N_min) method is generally accepted as the universal soil test for determining crop fertilizer requirements and predicting the possibility of groundwater contamination by excess nitrates (NO₃). However, it must be properly calibrated both for agronomic and environmental purposes. Since 1997, the program of soil monitoring for the content of N_min has been running in Poland. In 5,000 randomly selected sites on arable land, soil samples are collected twice a year (in early spring and autumn) from soil layers 0–30, 30–60, and 60–90 cm deep. The frozen samples are sent to the one of 17 regional agrochemical laboratories and analyzed for the content of nitrogen (N)–NO₃ and N‐ammonium (NH₄). The results, expressed in kg of N_min in the given soil layer and/or in the soil profile at 0–90 cm, are collected in the data bank at the Institute of Soil Science and Plant Cultivation, State Research Institute, Puławy. These data are made available for farmers and environment protection services. On the basis of about 75,000 data already collected, the calibration of N_min method was accomplished, and the results presented as the normatives of N_min content in spring and autumn. The distribution of data was far from normality, and therefore the median value was used as a characteristic of central point and percentile as a measure of distribution. Similar to the five classes of soil reaction and Phosphorus (P), potassium (K), and magnesium (Mg) contents officially used in Poland, five intervals of N_min content were proposed. Each interval contains 20% of ordered observations, and thus five classes of N_min were distinguished: very low, low, medium, high, and very high. Because of the significant N_min dependency on soil texture (very light, light, medium, heavy), altogether 20 normatives of N_min are included in the calibration table. In the article, the method of simulation of nitrate concentration in soil solution in the soil layer at 60–90 cm, assuming soil saturation to full water capacity, is presented as well.