Browsing by Subject "nitrogen fertilization"

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  • Vernay, Antoine; Tian, Xianglin; Chi, Jinshu; Linder, Sune; Makela, Annikki; Oren, Ram; Peichl, Matthias; Stangl, Zsofia R.; Tor-Ngern, Pantana; Marshall, John D. (2020)
    Gross primary production (GPP) is a key component of the forest carbon cycle. However, our knowledge of GPP at the stand scale remains uncertain, because estimates derived from eddy covariance (EC) rely on semi-empirical modelling and the assumptions of the EC technique are sometimes not fully met. We propose using the sap flux/isotope method as an alternative way to estimate canopy GPP, termed GPP(iso/SF), at the stand scale and at daily resolution. It is based on canopy conductance inferred from sap flux and intrinsic water-use efficiency estimated from the stable carbon isotope composition of phloem contents. The GPP(iso/SF)estimate was further corrected for seasonal variations in photosynthetic capacity and mesophyll conductance. We compared our estimate of GPP(iso/SF)to the GPP derived from PRELES, a model parameterized with EC data. The comparisons were performed in a highly instrumented, boreal Scots pine forest in northern Sweden, including a nitrogen fertilized and a reference plot. The resulting annual and daily GPP(iso/SF)estimates agreed well with PRELES, in the fertilized plot and the reference plot. We discuss the GPP(iso/SF)method as an alternative which can be widely applied without terrain restrictions, where the assumptions of EC are not met.
  • Kymäläinen, Anni (Helsingfors universitet, 2013)
    In Finland, potato is cultivated on more than 22 000 hectares, which makes it one of the most important crops. Potato is considered drought sensitivive because of it´s shallow roots. Thus, irrigation is recommended to improve not only the yield but to ensure good tuber quality. However irrigation is increases production costs. Nitrogen fertilization also affects yield and tuber quality but excess nitrogen can increase costs, nutrient leaching and reduce tuber quality. Thus, the equipment that can be used to estimate nutrient deficiencies have become more common. The effect of irrigation and nitrogen fertilization on growth and tuber yield of potato was investigated during 2001 – 2003 at Potato Research Institute in Lammi, Finland. Irrigation methods were surface irrigation and subsurface drip irrigation. Nitrogen was applied as a single dose when planting or as sidedress. Further interest was to find out whether SPAD values could be used to evaluate both the demand and timing of potato nitrogen fertilization. Irrigation did not affect potato development, tuber yield or starch content. Irrigation methods had no effect on tuber yield either. However, irrigation reduced the yield of marketable tuber yield. The benefit of drip irrigation was the possibility of combined irrigation and fertilizer application. Nitrogen increased tuber yield. The potato stand that received nitrogen as a single dose produced the greatest yield. However, even the potato stand which did not receive nitrogen produced quite large yield, over 30 tn/ha. In 2003, the stands which were given sidedress nitrogen with drip irrigation produced even greater yield than the ones that had been given nitrogen as a single dose. The stands which did not receive nitrogen had highest starch content. The SPAD values were used when estimating the demand of nitrogen fertilization with drip irrigation. SPAD measurements are easily conducted and non-destructive. SPAD values can be used to estimate the demand and timing of fertilization, even though there seems to be slight delay until the values indicate the nutrient deficiency.
  • Sihvonen, Matti Juhani; Hyytiäinen, Kari Petri; Valkama, Elena; Turtola, Eila (2018)
    Nitrogen (N) and phosphorus (P) are both essential plant nutrients. However, their joint response to plant growth is seldom described by models. This study provides an approach for modeling the joint impact of inorganic N and P fertilization on crop production, considering the P supplied by the soil, which was approximated using the soil test P (STP). We developed yield response models for Finnish spring barley crops (Hordeum vulgare L.) for clay and coarse-textured soils by using existing extensive experimental datasets and nonlinear estimation techniques. Model selection was based on iterative elimination from a wide diversity of plausible model formulations. The Cobb-Douglas type model specification, consisting of multiplicative elements, performed well against independent validation data, suggesting that the key relationships that determine crop responses are captured by the models. The estimated models were extended to dynamic economic optimization of fertilization inputs. According to the results, a fair STP level should be maintained on both coarse-textured soils (9.9 mg L-1 a(-1)) and clay soils (3.9 mg L-1 a(-1)). For coarse soils, a higher steady-state P fertilization rate is required (21.7 kg ha(-1) a(-1)) compared with clay soils (6.75 kg ha(-1) a(-1)). The steady-state N fertilization rate was slightly higher for clay soils (102.4 kg ha(-1) a(-1)) than for coarse soils (95.8 kg ha(-1) a(-1)). This study shows that the iterative elimination of plausible functional forms is a suitable method for reducing the effects of structural uncertainty on model output and optimal fertilization decisions.