Americas and Oceania Group - International Plant Nutrition Institute

Results so far indicate that it is possible to obtain high yields of maize and soybean (up to 12 t/ha and 5 t/
ha, respectively) by anticipating the P application to the winter forage crop (black oats or ryegrass). Second,
besides high grain yields, the anticipated P application leads to animal rate growth of up to 1 kg per day.
Third, in the first 2 years, the TSP performed better as related to other P sources. Fourth, in the last year, crop
response was higher with the MTP, and fifth, RP has performed as the least effective P source for this system.
This project is expected to continue providing more insights until 2015. Brazil-55
Rates and Residual Effect of Potassium Fertilization in a Brazilian Soil
Project Leader: Luís I. Prochnow, IPNI Brazil Program Director. E-mail: lprochnow@ipni.net
Project Cooperators: Valter Casarin, IPNI Brazil Deputy Director, and Eros Francisco, MT Research Foundation.
Potassium is, most generally, the second nutrient in terms of plant demand (after N). This nutrient
is responsible for several vital mechanisms for plant development and high yields (enzyme activation,
translocation and stock of compounds, osmotic regulation, water maintenance, etc). Potassium fertilizers are
a must for balanced plant nutrition in the acid soils of tropics, including Brazil. In many areas farmers are
cutting back on fertilizer expenses, which could compromise good yields, profit and food safety in the future.
The main objective of the study is to verify the effects of cutting back K fertilizer rates in some Brazilian
soils. The study is also looking at other important factors which may affect the K fertilizer effectiveness in
tropical soils (P, lime, phosphogypsum, time of application and locality effect) to evaluate 1) soil K status
with time, (2) plant K status with time, and (3) grain yield.
Main results for the first crop season (soybean and corn second crop) indicated: (1) low response to K in
soybean and no response in corn second crop, (2) no effect of lime, time of application, and location, and
(3) higher K leaf contents with phosphogypsum application in soybean but with no effect on yield. These
results indicate that we might be able to anticipate suppressing K application (after second crop year cycle
and not after third as previously planned) in future. It will be interesting to find out the effect of liming and
phosphogypsum application in deciding the K application suppression. This report summarizes data only for
the first cropping year, though the project is planned for 6 years. Brazil-56
Soil Physical Properties, Dynamics of Nitrogen, Phosphorus, and Potassium, and Crop Yield as Influenced by Soil
Compaction Under No-Till
Project Leader: Alvaro Pires da Silva, University of São Paulo Soil Science, Piracicaba, São Paulo.
E-mail: apisilva@usp.br
Project Cooperators: Neyde F.B. Giarol (UEPG), Cassio Tormena/UEPG, Bruce Ball/SAC – Scotland, João Carlos M.
Sá/UEPG, Adriel F. Fonseca (UEPG), and Marcos V. Milléo/UEPG.
The practice of no-till is gaining popularity for several reasons, chief among them being adequate soil
conservation in no-till areas. However, soil compaction has been noted as one of the main problems in areas
under no-till cultivation for years. Not plowing the soil, plus the traffic of machines in these areas, leads to
soil structure alterations resulting in poor soil physical quality and changes in the dynamics of N, P, and K.
These conditions can all contribute to crop yield reductions. This project was planned to integrate chemical
and physical evaluations of soils under no-till, foreseeing the need for future practical information to be
given to farmers on how to manage soil compaction so as to obtain higher yields. The experiment is located
in Ponta Grossa, Paraná, under a low fertility, acidic Oxisol high in clay, and under no-till for 20 years. The
treatments consist of: 1) maintaining regular no-till system (RNT), and 2) no-till submitted to mechanical subsoiling
(SNT). The study is evaluating: 1) visual soil structure quality, 2) soil water characteristics and soil
resistance, 3) soil hydraulic conductivity, 4) air permeability, 5) corn crop yield, and 6) leaf tissue analysis.
Results suggest some temporary improvement in soil physical quality in terms of soil structure and
hydraulic conductivity in the SNT treatment as opposed to the RNT. Such temporary improvement, however,
did not result in higher yields of corn and soybean. It is important to note that rainfall was adequate and well
distributed during the two crop seasons. This may have diminished the possibility for differences between
the two treatments, where advantages for the SNT would be expected. The higher concentration of P and K
in the plants under the SNT, noticed in the first year, are most likely because both nutrients are transported
to the root by diffusion. Thus, sub-soiling provided better conditions for plant root development, which in
turn resulted in more P and K contact and absorption, and consequently, higher P and K concentrations in
plants. New results for plant analysis are expected at the end of 2012 when this project completes. They might
provide some interesting and new insights. Brazil-57
46 IPNI Interpretive Summaries