|Soil and Water Management-69
A. SOIL FERTILITY AND MANAGEMENT
1. Analysis of soil and plant tissue
Soil and plant-tissue tests are being developed for rapid identification of soil fertility problems. Studies are under way on chemical changes in fertilizer materials in flooded soils that affect the movement and availability of fertilizers to rice. Calibration of soil and plant analysis tests are proceeding for determining the fertilizer needs of rice.
Also under study are nutritional factors limiting the growth of rice under flooded soil conditions, and fertility and management factors associated with yield decline on continuously cropped riceland.
2. Fertilizer application
Work continues on a new aircraft fertilizer-spreading device of significant potential in rice work. Patent rights are controlled by the University of Auckland, but we hope to get the machine tried out here.
Determining nitrogen needs of rice is one of the grower's greatest problems. A rapid, inexpensive colorimetric test has been developed for nitrogen in rice leaves. Results correlate extremely well (r - 0.976) with the standard Kjeldahl method. The new method is, however, faster, less expensive, and usable in the field.
Rate and method of fertilizer application have a great effect on the efficiency of utilization of nitrogen. Optimum depth of placement is shown to be 2 to 4 inches.
The effect of nitrogen topdressing at different stages of plant development on the yield and quality of rice was studied, and the effects of nitrogen applications at various growth stages on the yield components and quality of rice.
Other studies deal with nitrogen source and fertilizer use efficiency, and determination of optimum rate and time of nitrogen application for optimum rice yields. The slow release of nitrogen materials is being compared with urea in effectiveness and economy.
Studies are being conducted of soil incorporation of rice straw as it affects the growth yield, and nitrogen nutrition of rice. A residue trial aims at determining how much residue can be returned to the soil without harming rice production. The trial is designed to show the amount of nitrogen necessary to decompose the straw and produce a crop.
4. Zinc and iron
Method of application of zinc was studied for effect on efficiency of utilization. Zinc deficiency was corrected most readily and at lowest apparent cost by broadcast surface applications.
Studied in addition were various sources of zinc, and the synergistic effect of iron fertilizer materials on zinc uptake by rice.
Zinc and iron deficiencies were studied as causes of chlorosis and failure of stand establishment. The problem occurs most frequently on soils of high pH and where land leveling has been done. Most of the benefits from iron treatments in the past have derived from zinc contained in the material. Zinc can be applied more economically from other sources.
Other trials are designed to show whether zinc, iron, or possibly manganese are involved in the commonly termed "alkali-disease" of rice. Tissue sampling will be used in determining preliminary critical levels of zinc in the soil.
Need for potassium fertilization was studied on soils identified by plant analysis as being deficient. The studies involve sources, rates, and times of application.
6. Micronutrients in general
Two trials were held to determine the optimum rate of phosphorus to apply in deficient soils A secondary objective is to determine if phosphorus deficiency is a factor in poor rice growth between straw rows.
Seed treatment is being studied as a possible way of correcting problems of micronutrient deficiency in rice. Such treatment appears to be feasible in California.
B. IRRIGATION MANAGEMENT
Six strip-plots have been established to study water quality factors, including some pesticide residues, under different systems of water management. The systems involve deep and shallow water, with and without outflow from the lower end, and recirculation. Computer models are being tested to determine their value in predicting the suitability of water for growing rice and for disposing of it into public waters.
Small plot facilities have been developed at Davis to study the effects of irrigation practices on growth and yield of rice.
C. SEED SOAKING PRACTICES
Studies were made in 1960-70 on the effects of current soaking operations prior to sowing, on germination, seedling vigor and survival capacity. The studies were divided into three phases: 1) measurements of temperatures and 02 levels in rice bins during soaking operations; 2) laboratory tests of germination and growth under conditions similar to those in soaking bins; 3) field and laboratory tests on samples of seed withdrawn at intervals from positions in the soaking bins where 02 and temperature conditions are most stringent.
Measurements show that from the time a bin is drained the temperature begins to rise and the 02 level begins to fall. Within 20 hours of draining the 02 level reaches l% of gaseous volume, and by 48 hours the temperature reaches close to the lethal temperature of 105º F. Quantitative inhibition of shoot growth occurs when rice seeds are germinated under anaerobic conditions in the laboratory. However, no severe inhibition occurs unless the seeds are kept in low oxygen for at least 72 hours after inhibition. Qualitative observations suggest that root growth is even more severely inhibited This inhibition occurs after short periods without oxygen.
Samples were taken from the center of soaking bins at various intervals during the soaking process. The seed were tested for germination and growth rates in the laboratory and in field plots. The data are still being analyzed, and yield data will not be available until fall.