Management Measures and Technical Points for Rice during the Jointing and Panicle Elongation Stage

The jointing and panicle elongation stage refers to the period from jointing and the beginning of young panicle differentiation to just before heading, generally 25-36 days for middle-season rice.

1. Growth and development characteristics and growth appearance during the jointing and panicle elongation stage

(1) Growth and development characteristics During this period, on the one hand, stem elongation is the center, completing the growth of the last few leaves and root system and other vegetative organs; on the other hand, reproductive growth centered on young panicle differentiation takes place. During this period some tillers gradually die, and the total number of stems and tillers declines compared with the earlier stage, so it is an important period for preserving tillers and increasing panicles. Because of young panicle development, mainly spikelet differentiation, the differentiated spikelets cannot all set seed, so this period is also the key period for increasing flowers and grains and preserving flowers and grains that determines the number of grains per panicle, and the period that lays the foundation for grain filling and seed setting. Because the growth of various organs intensifies, the dry matter accumulated above ground in just one month accounts for about 50% of the total dry matter of the rice plant's whole life. Therefore, this period is the period when rice needs more water and fertilizer, and also the period most sensitive to external environmental conditions. Because the physiological metabolism of rice at this time shifts from being dominated by nitrogen metabolism in the earlier stage to both carbon and nitrogen metabolism flourishing, it not only requires abundant nitrogen nutrition to supply the growth of the last three leaves and surface roots and stem elongation, but must also accumulate sufficient carbohydrates and ensure their transport to the panicle to meet the needs of panicle development. The main direction of field management for high-yield cultivation is to preserve tillers and promote panicles, striving for large panicles. That is, to reduce the death of early tillers to increase the panicle-setting rate, make stems thick and strong with short basal internodes, enhance lodging resistance, prevent excessive leaf growth, promote spikelet differentiation and reduce spikelet degeneration, so as to achieve the goal of large panicles and many grains.

(2) Growth appearance Leaf color changes: it is required that "first yellow" appears at jointing and "second black" appears at booting, and then fades slightly when heading is about to occur, showing "second yellow". The row-closing stage is best when the flag leaf tip is emerging, because at this time the leaves have taken shape, the basal 4th and 5th internodes have basically completed elongation and filling, and even if shading occurs the effect is not great. Leaf length: the last 3 leaves should gradually become shorter, thick and upright; after heading the flag leaf tip should be level with or slightly higher than the panicle tip; a long, large and drooping flag leaf is a sign of excessive fertilization and overgrowth. The leaf area index reaches its maximum from booting to heading, then gradually decreases. The optimum leaf area index for high-yield rice at this stage varies with variety, plant type, leaf growth posture and cultivation management level. In Sichuan, Guizhou and Yunnan, a maximum leaf area index of 6-7 is generally suitable for medium and short-stature conventional rice, while hybrid rice can reach as high as 8 (medium japonica rice in Yunnan can reach as high as 8-8.9).

In short, the growth appearance required during the jointing and panicle elongation stage is: robust rice plant growth, thick and round basal stems, upright, green and elegant leaves, moderate top leaf length, and roots developing deep into the soil.

2. Field management measures

(1) Skillful application of panicle fertilizer Fertilizer applied as topdressing from the beginning of young panicle differentiation to heading is all called panicle fertilizer, and its application effect varies with different environments. If applied improperly, it not only fails to increase flowers and grains, but instead causes a high rate of empty and shriveled grains and reduced yield. Therefore, the application of panicle fertilizer should be comprehensively considered according to variety, climate, soil, the expected requirements of the high-yield structure and the ideal growth appearance. Generally, early-maturing varieties may not need it; for ordinary medium and late-maturing varieties and hybrid rice, on the basis of early application of tiller fertilizer, panicle fertilizer should also be applied, especially necessary for sandy fields with low fertility levels and weak fertilizer retention capacity. For fields with weak early growth, pale yellow leaf color at jointing, no dew on leaves in the morning, and upright leaves at noon, flower-promoting fertilizer should be applied; if "second black" is not obvious at booting, flower-preserving fertilizer should also be applied to increase the seed-setting rate and promote large panicles. Panicle fertilizer should be applied with a combination of nitrogen, phosphorus and potassium.

(2) Reasonable water management The panicle elongation stage is the period of greatest water demand in the life of rice. It is necessary to ensure no water shortage and no drought; generally fields should maintain a 30 mm water layer, so that the rice plant's absorption and transport of nutrients are smooth, the maximum photosynthetic efficiency is maintained, spikelet differentiation is promoted, and spikelet abortion is reduced. In cold and high-temperature areas, the water layer can be appropriately deepened to regulate temperature, making the soil temperature relatively stable and avoiding the effect of alternating high and low air temperatures on panicle differentiation. However, attention should also be paid to giving the soil conditions for aeration, so as to maintain root vigor and prevent premature aging.

(3) Prevention and control of diseases and insect pests The main insect pests in this period include stem borers, rice skipper, rice leaf roller and rice planthopper, etc., and armyworm also often occurs; the main diseases include sheath blight, bacterial leaf blight and rice blast, etc. Comprehensive measures should be taken to prevent and control them.